Voltage polarity converter, 15 volts 0,1 amps. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Voltage polarity converter, 15 volts 0,1 amps. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Voltage converters, rectifiers, inverters

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It is known that it is possible to fully realize the capabilities of operational amplifiers only when they are powered from a bipolar source. However, most often only a unipolar source is available in the home laboratory of a radio amateur. To power devices with a relatively small number of op-amps (consuming current up to 100 mA), you can use a converter that allows you to generate a bipolar voltage.

The converter (Fig. 4.27) consists of a rectangular pulse generator made on the elements DD1.1, DD1.2, a shaper on inverters DD1.3 ... DD1.6 connected in parallel (to increase the load capacity of the generator) and four switches: two - on transistors VT1, VT2 and VT3, VT4 and two - on diodes VD2, VD3 and VD4, VD5. Transistor keys for alternating current are connected in series, the signals at their input are antiphase.

(click to enlarge)

The frequency of rectangular pulses coming from the generator is about 10 kHz. However, the voltage on the capacitor C2 (as well as on the capacitor C3) is somewhat lower than the power supply voltage and depends on the load current (the larger it is, the greater the losses on the open transistor and diode). Therefore, to equalize the voltage of the shoulders, a resistor R8 is introduced. Capacitors C4 and C6 are used to eliminate parasitic excitation of the generator at high frequency. The circuit VD1, R3 allows you to bring the duty cycle of the output pulses of the generator closer to a value equal to two.

Without load, the converter consumes a current of about 20 mA. The range of ripple voltage at the output of the converter at a load current of 100 mA is no more than 5 mV.

The output impedance of the converter is approximately 10 ohms. If the converter will operate at a load current of up to 50 mA, it can be significantly simplified by abandoning the keys VT3, VT4 and VD4, VD5 - in this case the device becomes single-cycle. However, the load capacity of such a converter is much worse, and the ripple range (at a load current of 50 mA) reaches 25 mV. Transistors for the converter can have any letter index, but it is desirable to choose them with the highest possible static base current transfer coefficient.

Instead of KT502B, transistors KT313B can be used, and instead of KT503B - KT603B or KT608B. It should be noted that such a replacement may lead to a decrease in the voltage at the output of the lower arm of the converter by about 0,3 ... 0,7 V. Instead of D311A, diodes KD510A, KD522B are suitable.

Author: Semyan A.P.

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