Stabilized voltage converter. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Voltage converters, rectifiers, inverters
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The voltage converter, the circuit of which is shown in the figure, is designed to power portable radio equipment that consumes power no more than 10 watts. It is characterized by high efficiency, stable output voltage, and is not critical to the degree of battery discharge. The output voltage, when the input changes from 6 to 30 V, can be set anywhere from ±10 to ±20 V. In this case, the instability of the output voltage does not exceed 1%, and the ripple voltage (at a load of 2 kOhm) is 10 mV. The output impedance of the device is about 0,05 ohm.
According to the principle of operation, this is a key converter with a pulse-width modulation stabilizer. The master oscillator is made on inverters D1.1, D1.2 according to the scheme of a symmetrical multivibrator. The frequency of the generated oscillations is about 50 kHz. Through the diode V1, they go to the waiting multivibrator, assembled on inverters D1.3, D1.4. As can be seen from the diagram, in addition to the resistor R5 and capacitor C3, its frequency-setting circuit includes the resistance of the emitter-collector section of the transistor V3, the bias circuit of which (resistors R3, R4) is powered by a positive voltage taken from the output of the device. Due to this, the duration of the pulses generated by the multivibrator turns out to be inversely proportional to the output voltage (when it decreases, the duration of the pulses increases and vice versa). Trigger D1.5, D1.6 improves the shape of the pulses.
The pulse voltage taken from the trigger output is amplified in power by transistors V6, V7 and is increased by transformer T1 to the required value. The voltage rectified by the V8-V11 diodes enters the load through a filter consisting of electrolytic capacitors C6, C7 and ceramic capacitors C8, C9 shunting them (they improve the filtering of the high-frequency components of the rectified voltage). The output voltage of the converter is set by a tuning resistor R4.
The supply voltage of the transistor V6 and the D1 chip is maintained unchanged by a stabilizer made on the V5 transistor and the V4 zener diode.
The T1 transformer is made in a ferrite armored magnetic circuit with an outer diameter of 30 and a height of 18 mm. Winding I contains 17 turns of PEL 1,0 wire, winding II - 2X40 turns of PEL 0,23 wire.
If necessary (if the power consumed from the converter is close to the limit), the V7 transistor is installed on a heat sink with a cooling surface of 50 ... 60 sq. cm.
In the voltage converter, transistors KT373A (V3), KT801A, KT801B (V5, V6), diodes KD503A (V1, V2) can be used. D226D (V8-V11) and K155LN1 chip. For the manufacture of a pulse transformer, a ferrite armored magnetic circuit of the size M700NM-11 - B30-AL-630 is suitable.
Literature
"Radio, television, electronics" (NRB). 1981, No. 2
Publication: N. Bolshakov, rf.atnn.ru
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