Separate excitation switching power supply circuit diagram using free-running multivibrator as pulse generator

Published:2011/5/5 7:32:00 Author:Nicole | Keyword: switching power supply, multivibrator, pulse generator | From:SeekIC

As shown, VTlis the switch; VT2, VT3is push tube; VT4 is emitter follower. Separate excitation oscillation circuit is undertaken by free-running multivibrator which composed of VT5, VT6, C2, C3, R3, R4. VT7, VT8 form emitter-coupled differential amplifier to be used as the error amplification. Sampling circuit consists of resistors R7, R8 and in series with potentiometer R9. Voltage reference circuit is made of regulator diode VD4 and R5. Diode VDl, VD2 is used to prevent reverse voltage breakdown the push tube VT2, VT3 emitter. VD3 for the freewheeling diode; L for the energy storage inductor. The turn on/off of switch regulator is flipped by multivibrator, and controlled by emitter follower VT4. The flip time of multivibratoris determined by the error amplifier. In other words, The flip time of VT5 from the end to turnare decided by the current of VT8 charge to C3. The current of VT8 is larger, the deadline of VT5 is longer. Similarly, the flip time of VT6 from the end to turn is decided by the current of VT7 charge to C2. The current of VT7 is larger, the deadline of VT5 is shorter. When the output voltage isdropped for some reason, VT8 tube collector current of the differential amplifier decreases, tube collector current of VT7increases, so the conduction time of VT5 is shortened, and extended the deadline, leading to the longerconduction time of VT4 longer, the cut-off shorter, and ultimately the conduction time of control switch tubeis lengthening, the deadline is shortening,so that the output voltage to rise, remain the stability of output voltage.



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