In this article we will talk about the unipolar to bipolar voltage divider and its characteristics. We’ll also talk about its setup and operation.

With the development and spread of microelectronic technology, there is an increasingly urgent need to have a high-quality source of bipolar output voltage in your home laboratory. But as soon as radio amateurs encounter this, starting to look for various options for constructing bipolar power supplies, some of them become disappointed.

But these converters are not universal; they are also not capable of maintaining equality of positive and negative voltage, therefore they do not allow their use as bipolar power supplies with smooth regulation.

Thus, radio amateurs are faced with a choice: either simple circuit“fixed” bipolar voltage, or high-quality, but complex circuit block bipolar power supply.

I offer you another, and in my opinion, the highest quality solution to the problem - a special attachment to your existing unipolar power supply, which “divides” the unipolar constant pressure into two – positive and negative. The only limitation to using the device is the inability to use it with a power source whose plus or minus power is on the same ground as the load. For example - from battery car. This is due to the fact that the device “creates” its own “mass”. But the need to work in this mode is so insignificant that you can ignore this drawback.

Characteristics of a unipolar to bipolar voltage divider:

The presented voltage divider can be connected to any unipolar voltage unit in the range from 7 to 30 volts. In this case, the bipolar output voltage will be from 3 to 14.5 volts.

During operation, the divider does not degrade the parameters and characteristics of your unipolar power supply. Which is very important.

The divider provides bipolar power to an unbalanced load with a current of up to 10 amperes of each voltage (both positive and negative). In other words, if there is a load in the positive circuit with a current consumption of 10 amperes, and in the negative circuit 0.1 amperes, then the positive and negative voltages will differ by no more than 0.01 volts.

The bipolar output voltage is adjusted on the unipolar power supply itself. Therefore, if your power supply does not have this adjustment, then output voltage will not be regulated.

The presented unipolar voltage divider was tested with a universal stabilized power supply unit that I had previously developed. It showed excellent properties. Since my power supply produced voltage up to 26 volts, the output voltages ranged from 3 to +- 12.3 volts. After connecting additional turns of the secondary winding of the power transformer in the universal stabilized power supply circuit to a stabilized output voltage of 32 volts, the output voltages of the divider ranged from 3 to +- 15.2 volts. The automatic overload protection system also works reliably.

;The device has an adaptive circuit for monitoring and adjusting the equality of output voltages, regardless of possible changes in their amplitude and load.

The schematic diagram is shown in the figure.

Operation of a unipolar voltage divider

Operational amplifier DA1 measures the voltage difference at the midpoint of the voltage divider R1 - R2, R3 with the voltage on the “case” and reacts to their difference by increasing or decreasing the output voltage.

When power is supplied to the device, capacitors C1 and C2 are charged along the path “+” of the power supply, capacitor C1, capacitor C2, “-” of the power supply. Thus, each capacitor will be charged with half the input voltage. These voltages will be at the output of the device. But this will be observed under a balanced load.

Consider the case when an unbalanced load is connected to the device - for example, the load resistance in the positive output voltage circuit is much less than the load resistance connected to the negative output voltage circuit. Since a load circuit is connected in parallel to capacitor C1 - diode VD1 and low load resistance, the charge of capacitor C2 will pass not only through C1, but also through a circuit parallel to it - diode VD1, low load resistance. This will cause capacitor C2 to be charged with a higher voltage than capacitor C1, which in turn will cause the positive output voltage to be less than the negative one. On the device body, the voltage will increase in potential relative to the midpoint of resistors R1 - R2, R3, where the potential is equal to half the input voltage. This will lead to the appearance of a negative voltage at the output of the operational amplifier relative to the device body. And the greater the potential difference at the input of the operational amplifier, the greater the negative voltage. As a result of the negative voltage at the op-amp output, transistors VT3 and VT4 will open and, like the “diode VD1, low load resistance” circuit in the positive circuit, will create a shunt effect on capacitor C2 in the negative circuit. This in turn will lead to balancing of currents in the positive and negative circuits and equalize the output voltages. If the load of the device is unbalanced towards negative voltage, transistors VT1 and VT2 open.

Thus, due to the circuit of automatic control of the “zero” potential, it is balanced into the “average state” between the plus and minus of the supply.

Details.

Microcircuits K140UD6, K140UD7, K140UD601, K140UD701 can be used as an operational amplifier.

Resistors R8 - R15 - for equalizing the emitter currents of transistors and limiting their surges at switching moments.

Diodes VD1 and VD2 are designed to prevent transistors from shunting the load circuits of the device.

Transistors are installed on heat sinks of sufficient size. The size of the heat sinks is determined only by how unbalanced the load will be. The more unbalanced, the larger the radiator area.

Setting up a unipolar voltage divider.

A correctly assembled circuit starts working immediately. Resistor R3 is designed to set equal output bipolar voltages. It is more convenient to set it up on a dual-beam oscilloscope by connecting the bipolar outputs of the device to the inputs of the oscilloscope and turning on the mode of mutual subtraction of signals. By rotating the potentiometer slot, the maximum signal subtraction is set. If “beats” of the output voltage appear as a result of excitation and self-generation, it is necessary to reduce the value of resistor R5, while increasing the negative feedback.

The K140UD7 microcircuit is limited in power supply to 15 volts in the “arm”, so to obtain high output voltages it is necessary to connect power to pins 4 and 7 through “additional” zener diodes, but at the same time the lower level of output voltages will also increase.

This microcircuit provides the ability to adjust the zero balance using an external trimming resistor. When the supply voltage changes, it must be adjusted, so we do not use it in our circuit.

Due to the non-standard nature of the solution, the device designed to obtain bipolar voltage from unipolar voltage is unique. In terms of its simplicity and reliability of the circuit, this is the most The best way receiving bipolar power.

Not every radio amateur has the opportunity to get a suitable part, so you need to know what can replace it. Knowledge of electronic circuitry comes to the rescue. Given, as an example, is a simple circuit of a bipolar power supply using zener diodes, which well illustrates the principle of obtaining bipolar power from unipolar power.

Simple bipolar power supply circuit:

It can be difficult for a novice radio amateur to find a suitable transformer for power supplies, amplifier circuits, or other circuits that require bipolar power. An example is given of a classic scheme for obtaining a bipolar power supply from a unipolar one. It should be noted right away that I did not try to run this circuit, but cited it because the solution used is quite original and easy to implement (you should choose the values ​​of the elements yourself).

Figure No. 1 – Bipolar power supply diagram

This is a fairly simple circuit; it makes it possible to obtain positive and negative power poles from a transformer with only one secondary winding (one full-wave bridge rectifier, or from a unipolar power source). The solution is quite simple, two zener diodes in a pair provide voltage separation; you only need to ground their central point (the capacitor acting as a filter should not be grounded). The scheme is easy to implement, cheap and accessible, although it has its drawbacks.

In this article we will talk about the unipolar to bipolar voltage divider and its characteristics. We’ll also talk about its setup and operation.

With the development and spread of microelectronic technology, there is an increasingly urgent need to have a high-quality source of bipolar output voltage in your home laboratory. But as soon as radio amateurs encounter this, starting to look for various options for constructing bipolar power supplies, some of them become disappointed.

But these converters are not universal; they are also not capable of maintaining equality of positive and negative voltage, therefore they do not allow their use as bipolar power supplies with smooth regulation.

Thus, radio amateurs are faced with a choice: either a simple “fixed” bipolar voltage circuit, or a high-quality, but complex bipolar power supply circuit.

I offer you another, and in my opinion, the highest quality solution to the problem - a special attachment to your existing unipolar power supply, which “divides” the unipolar DC voltage into two - positive and negative. The only limitation to using the device is the inability to use it with a power source whose plus or minus power is on the same ground as the load. For example, from a car battery. This is due to the fact that the device “creates” its own “mass”. But the need to work in this mode is so insignificant that you can ignore this drawback.

Characteristics of a unipolar to bipolar voltage divider:

The presented voltage divider can be connected to any unipolar voltage unit in the range from 7 to 30 volts. In this case, the bipolar output voltage will be from 3 to 14.5 volts.

During operation, the divider does not degrade the parameters and characteristics of your unipolar power supply. Which is very important.

The divider provides bipolar power to an unbalanced load with a current of up to 10 amperes of each voltage (both positive and negative). In other words, if there is a load in the positive circuit with a current consumption of 10 amperes, and in the negative circuit 0.1 amperes, then the positive and negative voltages will differ by no more than 0.01 volts.

The bipolar output voltage is adjusted on the unipolar power supply itself. Therefore, if your power supply does not have this adjustment, then the output voltage will not be regulated.

The presented unipolar voltage divider was tested with a universal stabilized power supply unit that I had previously developed. It showed excellent properties. Since my power supply produced voltage up to 26 volts, the output voltages ranged from 3 to +- 12.3 volts. After connecting additional turns of the secondary winding of the power transformer in the universal stabilized power supply circuit to a stabilized output voltage of 32 volts, the output voltages of the divider ranged from 3 to +- 15.2 volts. The automatic overload protection system also works reliably.

;The device has an adaptive circuit for monitoring and adjusting the equality of output voltages, regardless of possible changes in their amplitude and load.

The schematic diagram is shown in the figure.

Operation of a unipolar voltage divider

Operational amplifier DA1 measures the voltage difference at the midpoint of the voltage divider R1 - R2, R3 with the voltage on the “case” and reacts to their difference by increasing or decreasing the output voltage.

When power is supplied to the device, capacitors C1 and C2 are charged along the path “+” of the power supply, capacitor C1, capacitor C2, “-” of the power supply. Thus, each capacitor will be charged with half the input voltage. These voltages will be at the output of the device. But this will be observed under a balanced load.

Consider the case when an unbalanced load is connected to the device - for example, the load resistance in the positive output voltage circuit is much less than the load resistance connected to the negative output voltage circuit. Since a load circuit is connected in parallel to capacitor C1 - diode VD1 and low load resistance, the charge of capacitor C2 will pass not only through C1, but also through a circuit parallel to it - diode VD1, low load resistance. This will cause capacitor C2 to be charged with a higher voltage than capacitor C1, which in turn will cause the positive output voltage to be less than the negative one. On the device body, the voltage will increase in potential relative to the midpoint of resistors R1 - R2, R3, where the potential is equal to half the input voltage. This will lead to the appearance of a negative voltage at the output of the operational amplifier relative to the device body. And the greater the potential difference at the input of the operational amplifier, the greater the negative voltage. As a result of the negative voltage at the op-amp output, transistors VT3 and VT4 will open and, like the “diode VD1, low load resistance” circuit in the positive circuit, will create a shunt effect on capacitor C2 in the negative circuit. This in turn will lead to balancing of currents in the positive and negative circuits and equalize the output voltages. If the load of the device is unbalanced towards negative voltage, transistors VT1 and VT2 open.

Thus, due to the circuit of automatic control of the “zero” potential, it is balanced into the “average state” between the plus and minus of the supply.

Details.

Microcircuits K140UD6, K140UD7, K140UD601, K140UD701 can be used as an operational amplifier.

Resistors R8 - R15 - for equalizing the emitter currents of transistors and limiting their surges at switching moments.

Diodes VD1 and VD2 are designed to prevent transistors from shunting the load circuits of the device.

Transistors are installed on heat sinks of sufficient size. The size of the heat sinks is determined only by how unbalanced the load will be. The more unbalanced, the larger the radiator area.

Setting up a unipolar voltage divider.

A correctly assembled circuit starts working immediately. Resistor R3 is designed to set equal output bipolar voltages. It is more convenient to set it up on a dual-beam oscilloscope by connecting the bipolar outputs of the device to the inputs of the oscilloscope and turning on the mode of mutual subtraction of signals. By rotating the potentiometer slot, the maximum signal subtraction is set. If “beats” of the output voltage appear as a result of excitation and self-generation, it is necessary to reduce the value of resistor R5, while increasing the negative feedback.

The K140UD7 microcircuit is limited in power supply to 15 volts in the “arm”, so to obtain high output voltages it is necessary to connect power to pins 4 and 7 through “additional” zener diodes, but at the same time the lower level of output voltages will also increase.

This microcircuit provides the ability to adjust the zero balance using an external trimming resistor. When the supply voltage changes, it must be adjusted, so we do not use it in our circuit.

Due to the non-standard nature of the solution, the device designed to obtain bipolar voltage from unipolar voltage is unique. Due to its simplicity and reliability of the circuit, this is the best way to obtain bipolar power.

Often, bipolar power supplies have a constant output voltage. The desire to construct an regulated one from an unregulated bipolar power supply at low cost usually does not lead to anything good, since this leads to an imbalance of the output voltages (in amplitude) of opposite polarities. To implement this option, it is necessary to significantly “weight” the scheme.

There is also an option when an electronic unit is added to a unipolar power supply, which generates a negative voltage from a positive one. But this version of a bipolar source also has an imbalance of opposite voltages and does not allow use in power supplies with continuously variable output voltage.

This article provides another original version bipolar power from unipolar having the right to exist. This is a prefix - built on operational amplifier LM358, to a conventional unipolar power supply, which allows you to obtain a full bipolar output voltage.

Any power supply with a voltage of 7...30 volts can act as an input voltage source, and the output voltage will be 3...14.5 volts.

During operation, this divider does not distort the output parameters of a unipolar power supply. This divider attachment can withstand a load of up to 10 amperes without distorting the voltage, both in the positive and negative channels. For example, if a load with a current consumption of 9 amperes is connected in the negative circuit of a bipolar power source, and 0.2 amperes in the positive circuit, then the difference between the negative and positive voltage will be less than 0.01 volts.

It should be noted that only the presence of a regulator in a unipolar power supply can ensure a change in the output in a bipolar one, otherwise adjustment will be impossible.

Description of the attachment-divider of unipolar voltage into bipolar

(DA1) measures the potential difference between the common wire and the midpoint of the voltage divider assembled at resistances R1, R2, R3. When this difference changes, the LM358 op-amp leads to stabilization of the output voltage, decreasing it or increasing it.

When input voltage is applied to the circuit, capacitors C1 and C2 are charged at half the supply voltage. With a balanced load, these voltages will be the output voltage of a bipolar power supply.

Now let's analyze the situation when an unbalanced load is connected to the output of a bipolar power supply, for example, the load resistance in the positive circuit is significantly lower than the load resistance connected to the negative circuit.

Since a load is connected in parallel to capacitor C1 (diode VD1 and a small load resistance), capacitor C2 will be charged both through capacitor C1 and through the above-designated circuit (diode VD1 and a small load resistance).

For this reason, capacitor C2 will be charged with a higher voltage than capacitor C1, and this will lead to the fact that the negative voltage will be higher than the positive one. On the common wire, the voltage will increase relative to the midpoint of the voltage divider R1, R2, R3, where the voltage is 50% of the input.

This contributes to the emergence of a negative voltage at the output of the op-amp LM358 relative to the common wire. As a result, transistors VT2 and VT4 open and, similarly to the electrical circuit “diode VD1, small load resistance” in the positive electrical circuit, bypasses capacitance C2 in the negative circuit, which leads to a balance of the currents of both circuits (positive and negative)

Likewise, transistors VT1, VT3 will open if there is a load imbalance towards negative voltage.

In the era of portable electronics, the issue of powering portable devices is becoming more and more pressing. Particularly difficult is the bipolar supply voltage required, for example, in a portable headphone amplifier. Today's development of electronics makes it possible to overcome this problem. Let's look at how to make bipolar power supply from unipolar one on the TPS65133 chip.

Bipolar power options for a portable device

Of course, for bipolar power supply in a portable device, you can use two batteries. But this will lead to additional difficulties with charging them, as well as imbalance of the arms as the batteries age.

A more advanced option to make bipolar power from unipolar is to use or any other. But there is a problem here too. When the battery is discharged, following the positive voltage, the negative voltage will also drop. Those. with a charged battery the power will be ±4.2, and with a discharged battery ±3 V or even less.

And here SEPIC converters come to the rescue. We will not delve into the theory of the transformation process - this is the topic of a separate article. For now, let's look at the unipolar to bipolar voltage converter on the TPS65133.

Bipolar power supply from unipolar one on the TPS65133 chip

The main advantage of this converter is that the output voltage is ±5V regardless of the input voltage, which can be from 2.9 to 5 volts (up to 6 volts can be supplied). Those. The microcircuit is designed for direct use with 3.6 volt batteries. But no one forbids powering it from USB or a power supply.

The conversion frequency here is 1.7 MHz. For audio devices this is great option. At the same time, operation does not require the use of transformers, which are needed in most SEPIC converters. The conversion requires only inductance which, due to such a high frequency, is quite small.

The circuit of the unipolar to bipolar voltage converter on the TPS65133 is as follows:

It is advisable to install tantalum capacitors. It would also be a good idea to install additional 0.1 µF capacitors to filter out RF interference.

As for such a parameter as output current, everything is very good here. The output current can reach 250 mA per arm. The manufacturer claims that with an output current of 50 to 200 mA, the efficiency of the converter exceeds 90%, which is a very good indicator for use in portable equipment.

Fly in the ointment

Despite all the obvious advantages, the biggest disadvantage of this microcircuit is its housing. The microcircuit is produced only in a package designed for surface mount, dimensions 3x3 mm. The dimensions of the contacts are 0.6x0.2 mm, and the distance between them is 0.25 mm.

Making a board with such contacts at home is not the easiest task. You can make your life easier if you buy a ready-made module with a soldered chip and wiring.

In general, TPS65133 is not the only one. In the same series there are TPS65130 TPS65131, TPS65132, TPS65135….. However, either their characteristics are less interesting, or the case is even worse.

I would be very grateful to anyone who can suggest microcircuits with similar characteristics. I'm waiting for you in the comments

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