Micropower stabilized voltage converter. Scheme, description

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Micropower stabilized voltage converter. 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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The device is intended for use in portable household and measuring equipment with autonomous power supply and power consumption of not more than 0,15 W. As you know, of particular importance for such power supplies is their efficiency.

Main technical characteristics:

Output power, W, no more ....... 0,15
Stabilization factor......100
Supply voltage (Up),V.......4...12
Conversion frequency, kHz.......20
Efficiency at an input voltage of 9 V and an output power of 40 mW, ....... 75
Double ripple amplitude, mV, at an output power of 40 mW.......50

The device described below is notable for its simplicity and good repeatability, it has a bipolar output. According to the principle of operation, the device is a key converter equipped with a stabilizer with SHI regulation. On the elements DD1.1 and DD1.2 (Fig. 1), a master oscillator operating at a frequency of 20 kHz is assembled. An alternating voltage from its output is fed to a single vibrator on the elements DD1.3, DD1.4. The duration of its output pulses depends on the total resistance included between the input of the element DD1.4 and the common wire. To increase the efficiency of the converter, the DD1 microcircuit is fed with a voltage of 3,6 V, removed from the stabilizer on transistors VT1, VT2.

Ris.1

The pulses from the output of a single vibrator are fed to the input of a power amplifier based on transistors VT3, VT4. At the moment when the transistors are open, a linearly increasing current flows through the primary winding of the transformer T1. When the transistors close, the polarity of the voltage on the primary winding changes and the energy accumulated in it is transferred to the load through the diodes VD1 and VD2. The feedback voltage from the winding III of the transformer T1 through a divider on resistors R9-R11 is supplied to the gate of the transistor VT5 operating in the variable resistor mode.

Reducing the voltage at the output of the converter from the set level causes a decrease in the negative voltage at the gate of the transistor VT5. The resistance of the transistor, and hence the time constant of the C4R6R7VT5 circuit, decrease. The duration of the negative pulses generated by the single vibrator becomes shorter. Since the frequency of the master oscillator is constant, the transistors VT3, VT4 open for a longer time and the output voltage returns to the set level.

Thus, the output voltage is maintained constant despite changes in the supply voltage and load current.

The time-setting elements of the single-vibrator are selected so that the duration of its output pulses is less than the duration of the oscillation period of the master oscillator in the entire range of input voltage changes, therefore, by the time a new trigger pulse arrives at the single-shot, it is already ready for operation.

Transformer T1 is wound on an annular magnetic circuit of size K12x5,5x5 made of M2000NM-A ferrite. All windings are the same and contain 100 turns of wire PEV-2 0,1. They are wound simultaneously, in three wires. A ring of a larger diameter with approximately the same cross section is also suitable for a transformer; magnetic permeability is also not critical. You can also use a ready-made pulse transformer MIT-4V.

Capacitors C1, C9, C10 - K53-14. Transistors KT3102BM can be replaced by any silicon npn structures, and KP103E - by KP103Zh, KP103I. Instead of the KP303I transistor, you can use KP303A, KP303B, KP303Zh. Diodes D9B can be replaced by any germanium.

A drawing of the circuit board is shown in fig. 2.

Ris.2

When setting up the converter, first, by selecting the resistor R3, a voltage of 3,6 V is set at the output of the stabilizer. Then, selecting the resistor R10 (roughly) and adjusting the tuning resistor R9 (fine), the required output voltage is achieved, and it is possible to obtain a voltage almost twice as high as indicated in the diagram , at the same output power.

If you need even more output voltage (for example, 2x15 V), you will have to increase the number of turns of the windings II and III of the transformer, respectively. In this case, the primary winding is first laid on the magnetic circuit, evenly distributing it along the ring, and then windings II and III are wound into two wires.

See other articles Section Voltage converters, rectifiers, inverters.

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