Buck type auxiliary electric power controlled by PFM

Abstract

The present invention discloses a buck auxiliary power supply controlled by PFM, which comprises a Buck conversion main circuit connected with input voltage +VIN, characterized in that control input end of the Buck conversion main circuit connects with a PFM control circuit, the PFM control circuit comprises a relaxation oscillator composed by a operational amplifier, and the output impulse controls conducting and switch off of the main switch tube of Buck conversion main circuit and allows Buck conversion main circuit output auxiliary power supply pressure VCC; the auxiliary power supply pressure VCC passes through a feedback circuit to connect with the relaxation oscillator; when the auxiliary power supply pressure higher than preset output pressure, the feedback circuit makes relaxation oscillator output impulse dutyfactor descend, and controls the Buck conversion main circuit output pressure reduce; when the auxiliary power supply pressure lower than the preset output pressure, the feedback circuit makes relaxation oscillator output impulse dutyfactor increase, and controls the Buck conversion main circuit output pressure raise so as to keep the auxiliary power supply output pressure stable.

Description

technical field The invention relates to a PFM control, non-isolated low power output auxiliary power supply for a control circuit in a high power density power supply module. Background technique In traditional high power density power supply modules, due to different circuit topologies, the auxiliary power supply is usually composed of the following methods: one is to provide auxiliary source voltage by the auxiliary winding wound on the high-power inductor; The auxiliary winding on the transformer provides the auxiliary source voltage; the third is to use a dedicated PWM (pulse width modulation) controller series switch circuit to provide the auxiliary source voltage. These three typical auxiliary source circuits are shown in Figure 1. The auxiliary source of the circuit in Figure 1(a) is mostly used for medium and high-power module power supplies of forward circuit topology. In high-power power modules using planar inductors, the inductor winding and auxiliary source ...

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Problems solved by technology

Because the power device and the control circuit are integrated together, although the volume is small, its application is limited by the withstand voltage of the power device, so it cannot be applied to the 48V bus system; in addition, the operating frequency of this control chip is fixed. The method is PWM control. Compared with PFM control with variable frequency, its no-load characteristics and light-load characteristics are poor

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