If you connect a resistor and a capacitor, you get perhaps one of the most useful and versatile circuits.

Today I decided to talk about the many ways to use it. But first, about each element separately:

The resistor's job is to limit the current. This is a static element whose resistance does not change; we are not talking about thermal errors now - they are not too large. The current through a resistor is determined by Ohm's law - I=U/R, where U is the voltage at the resistor terminals, R is its resistance.

The capacitor is a more interesting thing. It has an interesting property - when it is discharged, it behaves almost like a short circuit - the current flows through it without restrictions, rushing to infinity. And the voltage on it tends to zero. When it is charged, it becomes like a break and the current stops flowing through it, and the voltage across it becomes equal to the charging source. It turns out an interesting relationship - there is current, no voltage, there is voltage - no current.

To visualize this process, imagine a balloon... um... a balloon that is filled with water. The flow of water is a current. Water pressure on elastic walls is the equivalent of stress. Now look, when the ball is empty - water flows freely, there is a large current, but there is almost no pressure yet - the voltage is low. Then, when the ball is filled and begins to resist pressure, due to the elasticity of the walls, the flow rate will slow down, and then stop altogether - the forces are equal, the capacitor is charged. There is tension on the stretched walls, but no current!

Now, if you remove or reduce the external pressure, remove the power source, then the water will flow back under the influence of elasticity. Also, the current from the capacitor will flow back if the circuit is closed and the source voltage is lower than the voltage in the capacitor.

Capacitor capacity. What is this?
Theoretically, a charge of infinite size can be pumped into any ideal capacitor. It’s just that our ball will stretch more and the walls will create more pressure, infinitely more pressure.
What then about Farads, what is written on the side of the capacitor as an indicator of capacitance? And this is just the dependence of voltage on charge (q = CU). For a small capacitor, the voltage increase from charging will be higher.

Imagine two glasses with infinitely high walls. One is narrow, like a test tube, the other is wide, like a basin. The water level in them is tension. The bottom area is the container. Both can be filled with the same liter of water - equal charge. But in a test tube the level will jump by several meters, and in a basin it will splash at the very bottom. Also in capacitors with small and large capacitance.
You can fill it as much as you like, but the voltage will be different.

Plus, in real life, capacitors have a breakdown voltage, after which it ceases to be a capacitor, but turns into a usable conductor :)

How quickly does a capacitor charge?
Under ideal conditions, when we have an infinitely powerful voltage source with zero internal resistance, ideal superconducting wires and an absolutely flawless capacitor, this process will occur instantly, with time equal to 0, as well as the discharge.

But in reality there are always resistances, explicit - like a banal resistor or implicit, such as the resistance of wires or internal resistance voltage source.
In this case, the charging rate of the capacitor will depend on the resistance in the circuit and the capacitance of the capacitor, and the charge itself will flow according to exponential law.

And this law has a couple of characteristic quantities:

• T - time constant, this is the time at which the value reaches 63% of its maximum. 63% was not taken by chance; it is directly related to the formula VALUE T =max—1/e*max.
• 3T - and at three times the constant the value will reach 95% of its maximum.

Time constant for RC circuit T=R*C.

The lower the resistance and lower the capacitance, the faster the capacitor charges. If the resistance is zero, then the charging time is zero.

Let's calculate how long it will take for a 1uF capacitor to be charged to 95% through a 1kOhm resistor:
T= C*R = 10 -6 * 10 3 = 0.001c
3T = 0.003s After this time, the voltage on the capacitor will reach 95% of the source voltage.

The discharge will follow the same law, only upside down. Those. after T time, only 100% - 63% = 37% of the original voltage remains on the capacitor, and after 3T even less - a measly 5%.

Well, everything is clear with the supply and release of voltage. What if the voltage was applied, and then raised further in steps, and then discharged in steps as well? The situation here will practically not change - the voltage has risen, the capacitor has been charged to it according to the same law, with the same time constant - after a time of 3T its voltage will be 95% of the new maximum.
It dropped a little - it was recharged and after 3T the voltage on it will be 5% higher than the new minimum.
What am I telling you, it’s better to show it. Here in multisim I created a clever step signal generator and fed it to the integrating RC chain:

See how it wobbles :) Please note that both charge and discharge, regardless of the height of the step, are always of the same duration!!!

To what value can a capacitor be charged?
In theory, ad infinitum, a sort of ball with endlessly stretching walls. In reality, the ball will burst sooner or later, and the capacitor will break through and short-circuit. That's why all capacitors have important parameter — ultimate voltage. On electrolytes it is often written on the side, but on ceramic ones it must be looked up in reference books. But there it is usually from 50 volts. In general, when choosing a condenser, you need to ensure that its maximum voltage is not lower than that in the circuit. I will add that when calculating a capacitor for alternating voltage, you should choose a maximum voltage 1.4 times higher. Because on alternating voltage indicate effective value, and the instantaneous value at its maximum exceeds it by 1.4 times.

What follows from the above? What if you apply it to a capacitor constant pressure, then it will just charge and that’s it. This is where the fun ends.

What if you submit a variable? It is obvious that it will either charge or discharge, and current will flow back and forth in the circuit. Movement! There is current!

It turns out that, despite the physical break in the circuit between the plates, alternating current easily flows through the capacitor, but direct current flows weakly.

What does this give us? And the fact that a capacitor can serve as a kind of separator to separate alternating current and constant for the corresponding components.

Any time-varying signal can be represented as the sum of two components - variable and constant.

For example, a classical sinusoid has only a variable part, and the constant is zero. With direct current it is the opposite. What if we have a shifted sinusoid? Or constant with interference?

The AC and DC components of the signal are easily separated!
A little higher, I showed you how a capacitor is charged and discharged when the voltage changes. So the variable component will pass through the conder with a bang, because only it forces the capacitor to actively change its charge. The constant will remain as it was and will be stuck on the capacitor.

But in order for the capacitor to effectively separate the variable component from the constant, the frequency of the variable component must be no lower than 1/T

Two types of RC chain activation are possible:
Integrating and differentiating. They're a filter low frequencies and a high pass filter.

The low-pass filter passes the constant component without changes (since its frequency is zero, there is nowhere lower) and suppresses everything higher than 1/T. The direct component passes directly, and the alternating component is quenched to ground through a capacitor.
Such a filter is also called an integrating chain because the output signal is, as it were, integrated. Do you remember what an integral is? Area under the curve! This is where it comes out.

And it is called a differentiating circuit because at the output we get the differential of the input function, which is nothing more than the rate of change of this function.

• In section 1, the capacitor is charged, which means current flows through it and there will be a voltage drop across the resistor.
• In section 2, there is a sharp increase in the charging speed, which means the current will sharply increase, followed by a voltage drop across the resistor.
• In section 3, the capacitor simply holds the existing potential. No current flows through it, which means the voltage across the resistor is also zero.
• Well, in the 4th section the capacitor began to discharge, because... the input signal has become lower than its voltage. The current has gone in the opposite direction and there is already a negative voltage drop across the resistor.

And if we apply a rectangular pulse to the input, with very steep edges, and make the capacitance of the capacitor smaller, we will see needles like these:

rectangle. Well, what? That's right - the derivative of a linear function is a constant, the slope of this function determines the sign of the constant.

In short, if you are currently taking a math course, then you can forget about the godless Mathcad, disgusting Maple, throw the matrix heresy of Matlab out of your head and, taking out a handful of analog loose stuff from your stash, solder yourself a truly TRUE analog computer :) The teacher will be shocked :)

True, integrators and differentiators usually don’t make integrators and differentiators on resistors alone, here they use operational amplifiers. You can google for these things for now, interesting thing :)

And here I fed a regular rectangular signal to two high- and low-pass filters. And the outputs from them to the oscilloscope:

Here's a slightly larger section:

When starting, the condenser is discharged, the current through it is full, and the voltage on it is negligible - there is a reset signal at the RESET input. But soon the capacitor will charge and after time T its voltage will already be at the level of logical one and the reset signal will no longer be sent to RESET - the MK will start.
And for AT89C51 it is necessary to organize exactly the opposite of RESET - first submit a one, and then a zero. Here the situation is the opposite - while the condenser is not charged, then a large current flows through it, Uc - the voltage drop across it is tiny Uc = 0. This means that RESET is supplied with a voltage slightly less than the supply voltage Usupply-Uc=Upsupply.
But when the condenser is charged and the voltage on it reaches the supply voltage (Upit = Uc), then at the RESET pin there will already be Upit-Uc = 0

Analog measurements
But never mind the reset chains, where it’s more fun to use the RC circuit’s ability to measure analog values ​​with microcontrollers that don’t have ADCs.
This uses the fact that the voltage on the capacitor grows strictly according to the same law - exponential. Depending on the conductor, resistor and supply voltage. This means that it can be used as a reference voltage with previously known parameters.

It works simply, we apply voltage from the capacitor to an analog comparator, and connect the measured voltage to the second input of the comparator. And when we want to measure the voltage, we simply first pull the pin down to discharge the capacitor. Then we return it to Hi-Z mode, reset it and start the timer. And then the condenser begins to charge through the resistor, and as soon as the comparator reports that the voltage from the RC has caught up with the measured one, we stop the timer.

Knowing according to which law the reference voltage of the RC circuit increases over time, and also knowing how long the timer has been ticking, we can quite accurately find out what the measured voltage was equal to at the time the comparator was triggered. Moreover, it is not necessary to count exponents here. At the initial stage of charging the condenser, we can assume that the dependence there is linear. Or, if you want greater accuracy, approximate the exponential piecewise linear functions, and in Russian - draw its approximate shape with several straight lines or put together a table of the dependence of the value on time, in short, the methods are simple.

If you need to have an analog switch, but don’t have an ADC, then you don’t even need to use a comparator. Jiggle the leg on which the capacitor hangs and let it charge through a variable resistor.

By changing T, which, let me remind you, T = R * C and knowing that we have C = const, we can calculate the value of R. Moreover, again, it is not necessary to connect the mathematical apparatus here, in most cases it is enough to take measurements in some conditional parrots, like timer ticks. Or you can go the other way, not changing the resistor, but changing the capacitance, for example, by connecting the capacitance of your body to it... what will happen? That's right - touch buttons!

If something is not clear, then don’t worry, I’ll soon write an article about how to attach an analog piece of equipment to a microcontroller without using an ADC. I'll explain everything in detail there.

Capacitoris an element electrical circuit, which is capable of accumulating electric charge. An important feature of a capacitor is its ability not only to accumulate, but also to release charge, almost instantly.

According to the second law of commutation, the voltage across a capacitor cannot change abruptly. This feature is actively used in various filters, stabilizers, integrating circuits, oscillatory circuits, etc.

The fact that voltage cannot change instantly can be seen from the formula

If the voltage at the moment of switching changed abruptly, this would mean that the rate of change du/dt = ∞, which cannot happen in nature, since a source of infinite power would be required.

Capacitor charging process

The diagram shows an RC (integrating) circuit powered from a constant power source. When the key is closed to position 1, the capacitor is charged. The current passes through the circuit: “plus” of the source – resistor – capacitor – “minus” of the source.

The voltage on the capacitor plates changes exponentially. The current flowing through the capacitor also changes exponentially. Moreover, these changes are reciprocal; the higher the voltage, the less current flowing through the capacitor. When the voltage on the capacitor is equal to the source voltage, the charging process will stop and the current in the circuit will stop flowing.

Now, if we switch the key to position 2, then the current will flow in the opposite direction, namely through the circuit: capacitor - resistor - “minus” of the source. This will discharge the capacitor. The process will also be exponential.

An important characteristic of this circuit is the product R.C., which is also called time constantτ . During time τ, the capacitor is charged or discharged by 63%. In 5 τ, the capacitor gives up or receives the charge completely.

Let's move on from theory to practice. Let's take a 0.47 uF capacitor and a 10 kOhm resistor.

Let's calculate the approximate time for which the capacitor should charge.

Now let's assemble this circuit in multisim and try to simulate

The assembled circuit is powered by a 12 V battery. By changing the position of switch S1, we first charge and then discharge the capacitor through a resistance R = 10 KOhm. To clearly see how the circuit works, watch the video below.

Generators high voltage Low power is widely used in flaw detection, to power portable charged particle accelerators, X-ray and cathode ray tubes, photomultipliers, and ionizing radiation detectors. In addition, they are also used for electric pulse destruction of solids, production of ultrafine powders, synthesis of new materials, as spark leak detectors, for launching gas-discharge light sources, in electric-discharge diagnostics of materials and products, obtaining gas-discharge photographs using the S. D. Kirlian method , testing the quality of high-voltage insulation. In everyday life, such devices are used as power sources for electronic traps of ultrafine and radioactive dust, electronic ignition systems, for electroeffluvial chandeliers (chandeliers by A. L. Chizhevsky), aeroionizers, medical devices (D'Arsonval, franklization, ultratonotherapy devices ), gas lighters, electric fences, electric stun guns, etc.

Conventionally, we classify as high-voltage generators devices that generate voltages above 1 kV.

The high-voltage pulse generator using a resonant transformer (Fig. 11.1) is made according to the classical scheme using a gas spark gap RB-3.

Capacitor C2 is charged with a pulsating voltage through diode VD1 and resistor R1 to the breakdown voltage of the gas spark gap. As a result of breakdown of the gas gap of the spark gap, the capacitor is discharged onto the primary winding of the transformer, after which the process is repeated. As a result, damped high-voltage pulses with an amplitude of up to 3...20 kV are formed at the output of transformer T1.

To protect the output winding of the transformer from overvoltage, a spark gap made in the form of electrodes with an adjustable air gap is connected in parallel to it.

Rice. 11.1. Circuit of a high-voltage pulse generator using a gas spark gap.

Rice. 11.2. Circuit of a high-voltage pulse generator with voltage doubling.

Transformer T1 of the pulse generator (Fig. 11.1) is made on an open ferrite core M400NN-3 with a diameter of 8 and a length of 100 mm. The primary (low-voltage) winding of the transformer contains 20 turns of MGShV wire 0.75 mm with a winding pitch of 5...6 mm. The secondary winding contains 2400 turns of ordinary winding of PEV-2 wire 0.04 mm. The primary winding is wound over the secondary winding through a 2x0.05 mm polytetrafluoroethylene (fluoroplastic) gasket. The secondary winding of the transformer must be reliably isolated from the primary.

An embodiment of a high-voltage pulse generator using a resonant transformer is shown in Fig. 11.2. In this generator circuit there is galvanic isolation from the supply network. Mains voltage goes to the intermediate (step-up) transformer T1. The voltage removed from the secondary winding of the network transformer is supplied to a rectifier operating according to a voltage doubling circuit.

As a result of the operation of such a rectifier, a positive voltage appears on the upper plate of capacitor C2 relative to the neutral wire, equal to the square root of 2Uii, where Uii is the voltage on the secondary winding of the power transformer.

A corresponding voltage of the opposite sign is formed at capacitor C1. As a result, the voltage on the plates of the capacitor SZ will be equal to 2 square roots of 2Uii.

The charging rate of capacitors C1 and C2 (C1=C2) is determined by the value of resistance R1.

When the voltage on the plates of capacitor SZ is equal to the breakdown voltage of the gas gap FV1, a breakdown of its gas gap will occur, capacitor SZ and, accordingly, capacitors C1 and C2 will be discharged, and periodic damped oscillations will occur in the secondary winding of transformer T2. After discharging the capacitors and turning off the spark gap, the process of charging and subsequent discharging the capacitors to the primary winding of transformer 12 will be repeated again.

A high-voltage generator used to obtain photographs in a gas discharge, as well as to collect ultrafine and radioactive dust (Fig. 11.3) consists of a voltage doubler, a relaxation pulse generator and a step-up resonant transformer.

The voltage doubler is made using diodes VD1, VD2 and capacitors C1, C2. The charging chain is formed by capacitors C1 SZ and resistor R1. A 350 V gas spark gap is connected in parallel to capacitors C1 SZ with the primary winding of step-up transformer T1 connected in series.

As soon as the DC voltage level on capacitors C1 SZ exceeds the breakdown voltage of the spark gap, the capacitors are discharged through the winding of the step-up transformer and as a result a high-voltage pulse is formed. The circuit elements are selected so that the pulse formation frequency is about 1 Hz. Capacitor C4 is designed to protect the output terminal of the device from mains voltage.

Rice. 11.3. Circuit of a high voltage pulse generator using a gas spark gap or dinistors.

Output voltage the device is entirely determined by the properties of the transformer used and can reach 15 kV. A high-voltage transformer with an output voltage of about 10 kV is made on a dielectric tube with an outer diameter of 8 and a length of 150 mm; a copper electrode with a diameter of 1.5 mm is located inside. The secondary winding contains 3...4 thousand turns of PELSHO 0.12 wire, wound turn to turn in 10...13 layers (winding width 70 mm) and impregnated with BF-2 glue with interlayer insulation made of polytetrafluoroethylene. The primary winding contains 20 turns of PEV 0.75 wire passed through a polyvinyl chloride cambric.

As such a transformer, you can also use a modified horizontal scan output transformer of a TV; transformers for electronic lighters, flash lamps, ignition coils, etc.

The R-350 gas discharger can be replaced by a switchable chain of dinistors of the KN102 type (Fig. 11.3, right), which will allow the output voltage to be changed stepwise. To evenly distribute the voltage across the dinistors, resistors of the same value with a resistance of 300...510 kOhm are connected in parallel to each of them.

A variant of the high-voltage generator circuit using a gas-filled device, a thyratron, as a threshold-switching element is shown in Fig. 11.4.

Rice. 11.4. Circuit of a high voltage pulse generator using a thyratron.

The mains voltage is rectified by diode VD1. The rectified voltage is smoothed by capacitor C1 and supplied to the charging circuit R1, C2. As soon as the voltage on capacitor C2 reaches the ignition voltage of thyratron VL1, it flashes. Capacitor C2 is discharged through the primary winding of transformer T1, the thyratron goes out, the capacitor begins to charge again, etc.

An automobile ignition coil is used as transformer T1.

Instead of the VL1 MTX-90 thyratron, you can turn on one or more KN102 type dinistors. The amplitude of the high voltage can be adjusted by the number of included dinistors.

The design of a high-voltage converter using a thyratron switch is described in the work. Note that other types of gas-filled devices can be used to discharge a capacitor.

More promising is the use of semiconductor switching devices in modern high-voltage generators. Their advantages are clearly expressed: high repeatability of parameters, lower cost and dimensions, high reliability.

Below we will consider high-voltage pulse generators using semiconductor switching devices (dinistors, thyristors, bipolar and field-effect transistors).

A completely equivalent, but low-current analogue of gas dischargers are dinistors.

In Fig. Figure 11.5 shows the electrical circuit of a generator made on dinistors. The structure of the generator is completely similar to those described earlier (Fig. 11.1, 11.4). The main difference is the replacement of the gas discharger with a chain of dinistors connected in series.

Rice. 11.5. Circuit of a high-voltage pulse generator using dinistors.

Rice. 11.6. Circuit of a high-voltage pulse generator with a bridge rectifier.

It should be noted that the efficiency of such an analogue and switched currents are noticeably lower than that of the prototype, however, dinistors are more affordable and more durable.

A somewhat complicated version of the high-voltage pulse generator is shown in Fig. 11.6. The mains voltage is supplied to a bridge rectifier using diodes VD1 VD4. The rectified voltage is smoothed out by capacitor C1. This capacitor generates a constant voltage of about 300 V, which is used to power a relaxation generator composed of elements R3, C2, VD5 and VD6. Its load is the primary winding of transformer T1. Pulses with an amplitude of approximately 5 kV and a repetition frequency of up to 800 Hz are removed from the secondary winding.

The chain of dinistors must be designed for a switching voltage of about 200 V. Here you can use dinistors of the KN102 or D228 type. It should be taken into account that the switching voltage of dinistors of type KN102A, D228A is 20 V; KN102B, D228B 28 V; KN102V, D228V 40 V; KN102G, D228G 56 V; KN102D, D228D 80 V; KN102E 75 V; KN102Zh, D228Zh 120 V; KN102I, D228I 150 V.

A modified line transformer from a black-and-white TV can be used as a T1 transformer in the above devices. Its high-voltage winding is left, the rest are removed and instead a low-voltage (primary) winding is wound 15...30 turns of PEV wire with a diameter of 0.5...0.8 mm.

When choosing the number of turns of the primary winding, the number of turns of the secondary winding should be taken into account. It is also necessary to keep in mind that the value of the output voltage of the high-voltage pulse generator depends to a greater extent on the adjustment of the transformer circuits to resonance rather than on the ratio of the number of turns of the windings.

The characteristics of some types of horizontal scanning television transformers are given in Table 11.1.

Table 11.1. Parameters of high-voltage windings of unified horizontal television transformers.

Transformer type	Number of turns		R windings, Ohm
TVS-A, TVS-B
TVS-110, TVS-110M

Transformer type	Number of turns		R windings, Ohm
TVS-90LTs2, TVS-90LTs2-1
TVS-110PTs15
TVS-110PTs16, TVS-110PTs18

Rice. 11.7. Electrical diagram high-voltage pulse generator.

In Fig. Figure 11.7 shows a diagram of a two-stage high-voltage pulse generator published on one of the sites, in which a thyristor is used as a switching element. In turn, a gas-discharge device neon lamp (chain HL1, HL2) was chosen as a threshold element that determines the repetition rate of high-voltage pulses and triggers the thyristor.

When supply voltage is applied, the pulse generator, made on the basis of transistor VT1 (2N2219A KT630G), produces a voltage of about 150 V. This voltage is rectified by diode VD1 and charges capacitor C2.

After the voltage on capacitor C2 exceeds the ignition voltage of neon lamps HL1, HL2, the capacitor will be discharged through the current-limiting resistor R2 to the control electrode of thyristor VS1, and the thyristor will be unlocked. The discharge current of capacitor C2 will create electrical oscillations in the primary winding of transformer T2.

The thyristor switching voltage can be adjusted by selecting neon lamps with different ignition voltages. You can change the thyristor turn-on voltage stepwise by switching the number of neon lamps connected in series (or dinistors replacing them).

Rice. 11.8. Diagram of electrical processes on electrodes semiconductor devices(to Fig. 11.7).

The voltage diagram at the base of transistor VT1 and at the anode of the thyristor is shown in Fig. 11.8. As follows from the presented diagrams, the blocking generator pulses have a duration of approximately 8 ms. Capacitor C2 is charged exponentially in accordance with the action of pulses taken from the secondary winding of transformer T1.

Pulses with a voltage of approximately 4.5 kV are formed at the output of the generator. The output transformer for low-frequency amplifiers is used as transformer T1. As

High-voltage transformer T2 uses a transformer from a photo flash or a recycled (see above) horizontal scanning television transformer.

The diagram of another version of the generator using a neon lamp as a threshold element is shown in Fig. 11.9.

Rice. 11.9. Electrical circuit of a generator with a threshold element on a neon lamp.

The relaxation generator in it is made on elements R1, VD1, C1, HL1, VS1. It operates at positive line voltage cycles, when capacitor C1 is charged to the switching voltage of the threshold element on the neon lamp HL1 and thyristor VS1. Diode VD2 dampens self-induction pulses of the primary winding of step-up transformer T1 and allows you to increase the output voltage of the generator. The output voltage reaches 9 kV. The neon lamp also serves as an indicator that the device is connected to the network.

The high-voltage transformer is wound on a piece of rod with a diameter of 8 and a length of 60 mm made of M400NN ferrite. First, a primary winding of 30 turns of PELSHO 0.38 wire is placed, and then a secondary winding of 5500 turns of PELSHO 0.05 or larger diameter is placed. Between the windings and every 800... 1000 turns of the secondary winding, an insulation layer of polyvinyl chloride insulating tape is laid.

In the generator, it is possible to introduce discrete multi-stage adjustment of the output voltage by switching neon lamps or dinistors in a series circuit (Fig. 11.10). In the first version, two stages of regulation are provided, in the second - up to ten or more (when using KN102A dinistors with a switching voltage of 20 V).

Rice. 11.10. Electrical circuit of the threshold element.

Rice. 11.11. Electrical circuit of a high voltage generator with a diode threshold element.

A simple high-voltage generator (Fig. 11.11) allows you to obtain output pulses with an amplitude of up to 10 kV.

The control element of the device switches with a frequency of 50 Hz (at one half-wave of the mains voltage). The diode VD1 D219A (D220, D223) operating under reverse bias in avalanche breakdown mode was used as a threshold element.

When the avalanche breakdown voltage at the semiconductor junction of the diode exceeds the avalanche breakdown voltage, the diode transitions to a conducting state. The voltage from the charged capacitor C2 is supplied to the control electrode of the thyristor VS1. After turning on the thyristor, capacitor C2 is discharged into the winding of transformer T1.

Transformer T1 does not have a core. It is made on a reel with a diameter of 8 mm from polymethyl methacrylate or polytetrachlorethylene and contains three spaced sections with a width of

9 mm. The step-up winding contains 3x1000 turns, wound with PET, PEV-2 0.12 mm wire. After winding, the winding must be soaked in paraffin. 2 x 3 layers of insulation are applied on top of the paraffin, after which the primary winding is wound with 3 x 10 turns of PEV-2 0.45 mm wire.

Thyristor VS1 can be replaced with another one for a voltage higher than 150 V. The avalanche diode can be replaced with a chain of dinistors (Fig. 11.10, 11.11 below).

The circuit of a low-power portable high-voltage pulse source with autonomous power supply from one galvanic element (Fig. 11.12) consists of two generators. The first is built on two low-power transistors, the second on a thyristor and a dinistor.

Rice. 11.12. Voltage generator circuit with low-voltage power supply and thyristor-dinistor key element.

A cascade of transistors of different conductivities converts low-voltage direct voltage into high-voltage pulsed voltage. The timing chain in this generator is the elements C1 and R1. When the power is turned on, transistor VT1 opens, and the voltage drop across its collector opens transistor VT2. Capacitor C1, charging through resistor R1, reduces the base current of transistor VT2 so much that transistor VT1 comes out of saturation, and this leads to the closing of VT2. The transistors will be closed until capacitor C1 is discharged through the primary winding of transformer T1.

The increased pulse voltage removed from the secondary winding of transformer T1 is rectified by diode VD1 and supplied to capacitor C2 of the second generator with thyristor VS1 and dinistor VD2. In every positive half-cycle

The storage capacitor C2 is charged to an amplitude voltage value equal to the switching voltage of the dinistor VD2, i.e. up to 56 V (nominal pulse unlocking voltage for dinistor type KN102G).

The transition of the dinistor to the open state affects the control circuit of the thyristor VS1, which in turn also opens. Capacitor C2 is discharged through the thyristor and the primary winding of transformer T2, after which the dinistor and thyristor close again and the next capacitor charge begins; the switching cycle is repeated.

Pulses with an amplitude of several kilovolts are removed from the secondary winding of transformer T2. The frequency of spark discharges is approximately 20 Hz, but it is much less than the frequency of the pulses taken from the secondary winding of transformer T1. This happens because capacitor C2 is charged to the dinistor switching voltage not in one, but in several positive half-cycles. The capacitance value of this capacitor determines the power and duration of the output discharge pulses. The average value of the discharge current that is safe for the dinistor and the control electrode of the thyristor is selected based on the capacitance of this capacitor and the magnitude of the pulse voltage supplying the cascade. To do this, the capacitance of capacitor C2 should be approximately 1 µF.

Transformer T1 is made on a ring ferrite magnetic core of type K10x6x5. It has 540 turns of PEV-2 0.1 wire with a grounded tap after the 20th turn. The beginning of its winding is connected to the transistor VT2, the end to the diode VD1. Transformer T2 is wound on a coil with a ferrite or permalloy core with a diameter of 10 mm and a length of 30 mm. A coil with an outer diameter of 30 mm and a width of 10 mm is wound with PEV-2 0.1 mm wire until the frame is completely filled. Before winding is completed, a grounded tap is made, and the last row of wire of 30...40 turns is wound turn to turn over an insulating layer of varnished cloth.

The T2 transformer must be impregnated with insulating varnish or BF-2 glue during winding, then thoroughly dried.

Instead of VT1 and VT2, you can use any low-power transistors capable of operating in pulse mode. Thyristor KU101E can be replaced with KU101G. Power source galvanic cells with a voltage of no more than 1.5 V, for example, 312, 314, 316, 326, 336, 343, 373, or nickel-cadmium disk batteries type D-0.26D, D-0.55S and so on.

Thyristor high-voltage pulse generator with mains power supply shown in Fig. 11.13.

Rice. 11.13. Electrical circuit of a high-voltage pulse generator with a capacitive energy storage device and a thyristor switch.

During the positive half-cycle of the mains voltage, capacitor C1 is charged through resistor R1, diode VD1 and the primary winding of transformer T1. Thyristor VS1 is closed in this case, since there is no current through its control electrode (the voltage drop across diode VD2 in the forward direction is small compared to the voltage required to open the thyristor).

During a negative half-cycle, diodes VD1 and VD2 close. A voltage drop is formed at the cathode of the thyristor relative to the control electrode (minus at the cathode, plus at the control electrode), a current appears in the control electrode circuit, and the thyristor opens. At this moment, capacitor C1 is discharged through the primary winding of the transformer. A high voltage pulse appears in the secondary winding. And so on every period of mains voltage.

At the output of the device, bipolar high-voltage pulses are formed (since damped oscillations occur when the capacitor is discharged in the primary winding circuit).

Resistor R1 can be composed of three parallel-connected MLT-2 resistors with a resistance of 3 kOhm.

Diodes VD1 and VD2 must be rated for a current of at least 300 mA and reverse voltage not lower than 400 V (VD1) and 100 B (VD2). Capacitor C1 of the MBM type for a voltage of at least 400 V. Its capacitance (a fraction of a unit of microfarad) is selected experimentally. Thyristor VS1 type KU201K, KU201L, KU202K KU202N. Transformators B2B ignition coil (6 V) from a motorcycle or car.

The device can use a horizontal scanning television transformer TVS-110L6, TVS-1 YULA, TVS-110AM.

Enough typical scheme high-voltage pulse generator with capacitive energy storage is shown in Fig. 11.14.

Rice. 11.14. Scheme of a thyristor generator of high-voltage pulses with a capacitive energy storage device.

The generator contains a quenching capacitor C1, a diode rectifier bridge VD1 VD4, a thyristor switch VS1 and a control circuit. When the device is turned on, capacitors C2 and S3 are charged, thyristor VS1 is still closed and does not conduct current. The maximum voltage on capacitor C2 is limited by a zener diode VD5 of 9V. In the process of charging capacitor C2 through resistor R2, the voltage at potentiometer R3 and, accordingly, at the control transition of thyristor VS1 increases to a certain value, after which the thyristor switches to a conducting state, and capacitor SZ through thyristor VS1 is discharged through the primary (low-voltage) winding of transformer T1, generating a high voltage pulse. After this, the thyristor closes and the process begins again. Potentiometer R3 sets the response threshold of thyristor VS1.

The pulse repetition rate is 100 Hz. An automobile ignition coil can be used as a high-voltage transformer. In this case, the output voltage of the device will reach 30...35 kV. The thyristor generator of high-voltage pulses (Fig. 11.15) is controlled by voltage pulses taken from a relaxation generator made on dinistor VD1. The operating frequency of the control pulse generator (15...25 Hz) is determined by the value of resistance R2 and the capacitance of capacitor C1.

Rice. 11.15. Electrical circuit of a thyristor high-voltage pulse generator with pulse control.

The relaxation generator is connected to the thyristor switch through a pulse transformer T1 type MIT-4. A high-frequency transformer from the Iskra-2 darsonvalization apparatus is used as the output transformer T2. The voltage at the device output can reach 20...25 kV.

In Fig. Figure 11.16 shows an option for supplying control pulses to thyristor VS1.

The voltage converter (Fig. 11.17), developed in Bulgaria, contains two stages. In the first of them, the load of the key element, made on the transistor VT1, is the winding of the transformer T1. Rectangular control pulses periodically turn on/off the switch on transistor VT1, thereby connecting/disconnecting the primary winding of the transformer.

Rice. 11.16. Option for controlling a thyristor switch.

Rice. 11.17. Electrical circuit of a two-stage high-voltage pulse generator.

An increased voltage is induced in the secondary winding, proportional to the transformation ratio. This voltage is rectified by diode VD1 and charges capacitor C2, which is connected to the primary (low-voltage) winding of high-voltage transformer T2 and thyristor VS1. The operation of the thyristor is controlled by voltage pulses taken from the additional winding of transformer T1 through a chain of elements that correct the shape of the pulse.

As a result, the thyristor periodically turns on/off. Capacitor C2 is discharged onto the primary winding of the high-voltage transformer.

High-voltage pulse generator, fig. 11.18, contains a generator based on a unijunction transistor as a control element.

Rice. 11.18. Circuit of a high-voltage pulse generator with a control element based on a unijunction transistor.

The mains voltage is rectified by the diode bridge VD1 VD4. The ripples of the rectified voltage are smoothed out by capacitor C1; the charging current of the capacitor at the moment the device is connected to the network is limited by resistor R1. Through resistor R4, capacitor S3 is charged. At the same time, a pulse generator based on a unijunction transistor VT1 comes into operation. Its “trigger” capacitor C2 is charged through resistors R3 and R6 from a parametric stabilizer (ballast resistor R2 and zener diodes VD5, VD6). As soon as the voltage on capacitor C2 reaches a certain value, transistor VT1 switches, and an opening pulse is sent to the control transition of thyristor VS1.

Capacitor SZ is discharged through thyristor VS1 to the primary winding of transformer T1. A high voltage pulse is formed on its secondary winding. The repetition rate of these pulses is determined by the frequency of the generator, which, in turn, depends on the parameters of the chain R3, R6 and C2. Using the tuning resistor R6, you can change the output voltage of the generator by about 1.5 times. In this case, the pulse frequency is regulated within the range of 250... 1000 Hz. In addition, the output voltage changes when selecting resistor R4 (ranging from 5 to 30 kOhm).

It is advisable to use paper capacitors (C1 and SZ for a rated voltage of at least 400 V); The diode bridge must be designed for the same voltage. Instead of what is indicated in the diagram, you can use the T10-50 thyristor or, in extreme cases, KU202N. Zener diodes VD5, VD6 should provide a total stabilization voltage of about 18 V.

The transformer is made on the basis of TVS-110P2 from black and white televisions. All primary windings are removed and 70 turns of PEL or PEV wire with a diameter of 0.5...0.8 mm are wound onto the vacant space.

Electrical circuit of a high voltage pulse generator, Fig. 11.19, consists of a diode-capacitor voltage multiplier (diodes VD1, VD2, capacitors C1 C4). Its output produces a constant voltage of approximately 600 V.

Rice. 11.19. Circuit of a high-voltage pulse generator with a mains voltage doubler and a trigger pulse generator based on a unijunction transistor.

A unijunction transistor VT1 type KT117A is used as a threshold element of the device. The voltage at one of its bases is stabilized by a parametric stabilizer based on a VD3 zener diode of type KS515A (stabilization voltage 15 B). Through resistor R4, capacitor C5 is charged, and when the voltage at the control electrode of transistor VT1 exceeds the voltage at its base, VT1 switches to a conducting state, and capacitor C5 is discharged to the control electrode of thyristor VS1.

When the thyristor is turned on, the chain of capacitors C1 C4, charged to a voltage of about 600...620 V, is discharged into the low-voltage winding of the step-up transformer T1. After this, the thyristor turns off, the charge-discharge processes are repeated with a frequency determined by the constant R4C5. Resistor R2 limits the current short circuit when the thyristor is turned on and at the same time it is an element of the charging circuit of capacitors C1 C4.

The converter circuit (Fig. 11.20) and its simplified version (Fig. 11.21) is divided into the following components: network suppression filter (interference filter); electronic regulator; high voltage transformer.

Rice. 11.20. Electrical circuit of a high voltage generator with surge protector.

Rice. 11.21. Electrical circuit of a high voltage generator with a surge protector.

Scheme in Fig. 11.20 works as follows. The capacitor SZ is charged through the diode rectifier VD1 and resistor R2 to the amplitude value of the network voltage (310 V). This voltage passes through the primary winding of transformer T1 to the anode of thyristor VS1. Along the other branch (R1, VD2 and C2), capacitor C2 is slowly charged. When, during its charging, the breakdown voltage of dinistor VD4 is reached (within 25...35 V), capacitor C2 is discharged through the control electrode of thyristor VS1 and opens it.

Capacitor SZ is almost instantly discharged through the open thyristor VS1 and the primary winding of transformer T1. The pulsed changing current induces a high voltage in the secondary winding T1, the value of which can exceed 10 kV. After the discharge of the capacitor SZ, the thyristor VS1 closes and the process repeats.

A television transformer is used as a high-voltage transformer, from which the primary winding is removed. For the new primary winding, a winding wire with a diameter of 0.8 mm is used. Number of turns 25.

For the manufacture of barrier filter inductors L1, L2, high-frequency ferrite cores are best suited, for example, 600NN with a diameter of 8 mm and a length of 20 mm, each having approximately 20 turns of winding wire with a diameter of 0.6...0.8 mm.

Rice. 11.22. Electrical circuit of a two-stage high-voltage generator with a field-effect transistor control element.

A two-stage high-voltage generator (author Andres Estaban de la Plaza) contains a transformer pulse generator, a rectifier, a timing RC circuit, a key element on a thyristor (triac), a high-voltage resonant transformer and a thyristor operation control circuit (Fig. 11.22).

Analogue of transistor TIP41 KT819A.

Low voltage transformer voltage converter with crossover feedback, assembled on transistors VT1 and VT2, produces pulses with a repetition frequency of 850 Hz. To facilitate operation when large currents flow, transistors VT1 and VT2 are installed on radiators made of copper or aluminum.

The output voltage removed from the secondary winding of transformer T1 of the low-voltage converter is rectified by the diode bridge VD1 VD4 and charges capacitors S3 and C4 through resistor R5.

The thyristor switching threshold is controlled by a voltage regulator, which includes field-effect transistor VTZ.

Further, the operation of the converter does not differ significantly from the previously described processes: periodic charging/discharging of capacitors occurs on the low-voltage winding of the transformer, and damped electrical oscillations are generated. The output voltage of the converter, when used at the output as a step-up transformer of an ignition coil from a car, reaches 40...60 kV at a resonant frequency of approximately 5 kHz.

Transformer T1 (output horizontal scan transformer) contains 2x50 turns of wire with a diameter of 1.0 mm, wound bifilarly. The secondary winding contains 1000 turns with a diameter of 0.20...0.32 mm.

Note that modern bipolar and field-effect transistors can be used as controlled key elements.

Human contact with a circuit with residual charge. The term residual refers to the amount of charge remaining on certain time in the circuit after removing the voltage from it. Electrical equipment, in this case, has a capacitance and, as a capacitor, maintains potential relative to ground.

Accidental contact of a person with a charged container leads to its discharge and drainage of potential by current. I h through the body to the ground.

Conditions for creating a current circuit. The capacitance of the electrical circuit relative to ground and between phases depends on design features equipment. The length of the line, its type (cable or overhead), the state of insulation, grounding of live parts affect the size of the capacitance and residual charge, respectively.

It is important to understand that in order to charge the circuit’s capacity, it is not necessary to connect it to the main power source and then disconnect it. There are other, less noticeable and therefore dangerous ways to create capacitive potential.

When working with a megohmmeter, the device voltage is applied between the buses under test (all or individually) and/or ground. A capacitive charge occurs, which persists for a long time.

Therefore, after each operation it should be removed with a prepared portable grounding device.

Transformer devices in the disconnected state are subject to checks of the polarity of the windings. To do this, a small constant voltage of up to 6 volts is pulsed and removed into one winding and controlled in the second by measuring instruments. If a person comes into contact with this winding, he or she will be injured by the transformed impulse.

The single phase circuit below shows possible way getting injured.

Laboratory work No. 6

STUDYING THE PROCESS OF CHARGING AND DISCHARGING A CAPACITOR

GOAL OF THE WORK

Study of the processes of charging and discharging capacitors in R.C.- circuits, familiarization with the operation of devices used in pulsed electronic technology.

THEORETICAL BASIS OF WORK

Let's consider the diagram shown in Fig. 1. The circuit includes a source direct current, active resistance and capacitor, in which we will consider the processes of charge and discharge. We will analyze these processes separately.

Capacitor discharge.

Let first a current source e be connected to a capacitor C through a resistance R. Then the capacitor will charge as shown in Fig. 1. Let's move key K from position 1 to position 2. As a result, the capacitor is charged to voltage e, will begin to discharge through resistance R. Considering the current positive when it is directed from the positively charged plate of the capacitor to the negatively charged one, we can write

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Where i– instantaneous value of current in the circuit, the minus sign of which indicates that the appearance of current in the circuit i associated with a decrease in charge q on the capacitor;

q And WITH– instantaneous values ​​of charge and voltage on the capacitor.

Obviously, the first two expressions represent the definitions of current and electrical capacity, respectively, and the last is Ohm's law for a section of the circuit.

From the last two relations we express the current strength i in the following way:

https://pandia.ru/text/78/025/images/image006_31.gif" width="113" height="53 src=">. (2)

18. Why is there no DC source shown in the circuit diagram in this installation?

19. Is it possible to use a sinusoidal voltage generator or a sawtooth voltage generator in this installation?

20. What frequency and duration of pulses should the generator produce?

21. Why is active resistance needed in this circuit? R? What should its size be?

22. What types of capacitors and resistors can be used in this installation?

23. What values ​​can capacitance and resistance have in this circuit?

24. Why is oscilloscope signal synchronization needed?

25. How do they achieve optimal type signal on the oscilloscope screen? What adjustments apply?

26. What is the difference between the charge and discharge circuits of a capacitor?

27. What measurements need to be taken to determine the capacitance of the capacitor in R.C.-chains?

28. How to evaluate measurement errors during operation of the installation?

29. How to improve the accuracy of determining relaxation time R.C.-chains?

30. Name ways to improve the accuracy of determining the capacitance of a capacitor.