Voltage stabilizer on the comparator, 19-30/5 volts 2 amps. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Surge Protectors
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The voltage stabilizer (Fig. 5.12) works as follows. The comparator compares the sawtooth exemplary voltage with part of the output voltage taken from the divider R8, R9. As long as the output voltage is greater than the reference voltage, the key transistor is closed. As soon as the sawtooth voltage exceeds the output, the comparator signal will open this transistor.
The lower the voltage at the output of the stabilizer, the longer the transistor will be open. After the sawtooth voltage drops, the transistor closes and the L2 choke circuit - the load closes through the powerful diode VD3 that has opened at that moment. As soon as the key transistor opens, the VD3 diode immediately closes. The input filter weakens the penetration of impulse noise into the supply network, the output filter - into the load.
(click to enlarge)
Main technical characteristics:
- output voltage, V.....5;
- load current, A .... 2;
- ripple voltage, mV.....50;
- stabilization coefficient ..... 100;
- switching frequency, kHz.....25.
In the stabilizer, you can use the comparator K554SAZA, K554SAZB or K521SAZ (but it has a different pinout). The KT908A transistor can be replaced by any other powerful high-frequency silicon npn transistor or a powerful low-frequency one from the KT805, KT808, KT819 series. But when using a low-frequency transistor, the heat losses in it will increase (at a current of no more than 1 A, the output transistor can operate without a heat sink). Transistor VT3 - any of the KT814 series. The KD213A diode can be replaced with any other of this series, or a collector junction of a powerful high-frequency transistor can be used instead.
Inductors L1 and L3 are wound on segments of a rod with a diameter of 8 and a length of 20 mm made of 600NN ferrite and contain 10 turns of insulated copper wire with a diameter of 1,2 mm. The magnetic circuit of the throttle L2 - armored B26 from ferrite 2000NM; between its cups make a gasket 0,2 mm thick from a non-magnetic material. The winding containing 20 turns is made with a bundle of five PEV-2-0,25 conductors.
Checking the device begins with measuring the voltage at the zener diodes VD1, VD2. An oscilloscope is connected to the emitter of a unijunction transistor and, by connecting other capacitors of different capacities in parallel with capacitor C2, by changing the frequency, they are convinced that the sawtooth voltage generator is working. Then a dummy load is connected to the device and the required output voltage is set with resistor R4.
Next, the oscilloscope is connected to the VD3 diode and rectangular pulses are observed. The shape of the pulses can be improved by selecting the resistor R6 and the gap in the armored magnetic circuit of the inductor L2.
Author: Semyan A.P.
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