Switching power supply with multi-stage Darlington transistor

Abstract

The invention discloses a switching power supply with a multi-stage Darlington transistor. The switching power supply comprises a transformer (1), a switching tube (2), a controller (2) and a bleeder circuit. The switching tube (2) is the Darlington transistor formed by at least two stages of NPN triodes, and the controller (3) comprises a sampling unit (31), a first comparator (32), a pulse frequency modulation unit (33), a logic and drive unit (34), a first MOS (metal oxide semiconductor) tube (M1), a second MOS tube (M2) and a current source (35). The switching power supply has advantages that by use of the multi-stage Darlington transistor as the switching tube, base drive current of the switching tube can be greatly lowered so as to reduce power consumption of the controller, chip temperature rise is reduced, and a driving power upper limit is substantially raised; in addition, power supply capacitance can be decreased correspondingly, so that system cost is saved.

Description

technical field [0001] The invention relates to the technical field of power supplies, in particular to a switching power supply with multi-stage Darlington tubes. Background technique [0002] Switching power supply is a kind of power supply that uses modern power electronic technology to control the time ratio of switching on and off to maintain a stable output voltage. [0003] The original switching tube is made of Metal Oxide Semiconductor (MOS for short), but due to the cost advantage of NPN transistors, more and more switching power supplies use NPN transistors instead of MOS transistors as switching tubes. However, when using NPN When the triode is used as a switching tube, the control chip needs to provide a large base current for the switching tube, which may easily cause a large power loss and cause serious heating problems in the control chip. Moreover, because the required base current is too large, it is necessary to Configure a large power supply capacitor to...

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Problems solved by technology

[0003] The original switching tube is made of Metal Oxide Semiconductor (MOS for short), but due to the cost advantage of NPN transistors, more and more switching power supplies use NPN transistors instead of MOS transistors as switching tubes. However, when using NPN When the triode is used as a switch tube, the control chip needs to provide a large base current for the switch tube, which will easily cause a large power loss and cause serious heating problems in the control chip. Moreover, because the required base current is too large, it is necessary to Configure a large power supply capacitor to maintain the power supply voltage when the control chip is working, which will affect the startup speed and increase the preparation cost of the switching power supply

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