Published:2011/3/27 22:07:00 Author:Nicole | Keyword: switching power supply, single-junction transistor, pulse generator | From:SeekIC
As shown: VD1 ~ VD4 and C1 is the rectifier filter circuit, turning the 220V AC mains voltage into 300V DC. Pulse generator consists of a single junction transistor VT1, resistors R3, R4, R5, potentiometer RP and capacitor C3, with the change of potentiometer's resistance, the pulse frequency is changed. C4 for coupling capacitor of the output pulse. Rl and R2 make 300V DC divider to a single-junction transistor VTl, and provide 20 ~ 30V operating voltage. VT2 is the inverting amplifier tube, inverted and amplified the output positive pulse of the pulse generator, transport a negative pulse to switch VT4, so that it is ended when VT1 output positive pulse.
VT3, R7, C5 form the protection circuit of switch VT4. When connected to power supply, and the pulse generator has not worked, VT4 is on, the pressure drop on R7 increases, make the base bias of VT3 increase, cause the collector current Ic3 increased, the pressure drop Uce3 reduced, base potential of VT4 tube decreased, limiting the collector current of VT4 Ic4, so that it is remained in the security value.
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