Published:2011/4/1 3:56:00 Author:Nicole | Keyword: switching power supply, self-excited multivibrator, pulse generator | From:SeekIC
As shown, separately excited switching power supply circuit which used self-excited multivibrator as pulse generator, VTlis the switch tube; VT2, VT3are the push tubes; VT4is the emitter follower. Self-excited multivibrator as the separately excited oscillation circuit is composed of VT5, VT6, C2, C3, R3, R4 and so on. The emitter-coupled differential amplifier is made of VT7, VT8 which as the error amplification. Sampling circuit consists of resistors R7, R8 and R9 potentiometer in series. The reference voltage circuit composed of diode VD4 and R5. Diode VDl, VD2 is used to prevent the push tube VT2, VT3 emitter reversing voltage breakdown. VD3 for the after flow diode; L for the energy storage inductor. The turn-on and cut-off of switching regulator is flipped by the multivibrator, and controlled by emitter follower VT4. The time of multivibrator flip is determined by the error amplifier. The flip time of VT5 from the end to turn is determined by the charge current of VT8 to the C3. VT8 current is larger, the deadline of VT5 is longer. Similarly, The flip time of VT6 from the end to turn is determined by the charge current of VT7 to the C2 VT7 current is larger, the deadline of VL is shorter. When the output voltage down for some reason, VT8 tube collector current of the differential amplifier is decreased, VT7 tube collector current increases, so the conduction time of VT5 is shortened, extended the deadline, leading to the conduction time of VT4 longer, the deadline shorter, and ultimately the conduction time of control switch lengthened, shortened the deadline, so that the output voltage to rise, keep output voltage steady.
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