Starting circuit and switch power source thereof

Abstract

The invention discloses a switching power source and a starting circuit of the switching power source, wherein, the starting circuit is used for the power supply of a PWM control chip that is used for controlling the switching of the power FET; under the starting mode, the power for the PWM controlling chip is supplied by a starting circuit capacitor with smaller capacity value, thereby guaranteeing that the system has short starting time; after the starting is successful, under the normal working mode, a larger capacitor is connected with the starting circuit capacitor in parallelism through a switch to supply power for the PWM controlling chip, thereby reducing the ripples of the power-supply voltage of the switching power source in normal work and improving the stability of the system. Using the switching power source of the starting circuit prevents a high-voltage element from being introduced into the PWM controlling chip, thereby reducing the production process requirement of the chip, reducing the production cost of the PWM chip and reducing the starting time of the system as far as possible while reducing the power consumption.

Description

technical field [0001] The invention relates to the technical field of switching power supplies, in particular to a starting circuit for providing electric energy to a switching power supply controller and a switching power supply using the starting circuit. Background technique [0002] At present, the switching power supply circuit uses a PWM (abbreviation for pulse width modulation) control chip to control the power FET to turn on or off. Many switching power supply systems require high-voltage devices integrated in the PWM chip to form a startup circuit. Generate the lower bias voltage required inside the chip. This not only puts forward requirements on the design of the chip, but more importantly, this solution requires the wafer factory to provide devices that can withstand quite high voltage. But in fact, not every wafer manufacturer can meet the requirements, and high-voltage resistant devices are often much higher in price than ordinary devices. US Patent US 55814...

AI Technical Summary

Problems solved by technology

One of the disadvantages of this structure is that it is easy to cause the degradation of the switching transistor, because the switching transistor stops conduction by reverse biasing the base-emitter junction; another disadvantage of the above scheme is the need for high voltage withstand devices

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