Frequency soft start control circuit

Abstract

The invention relates to a frequency soft start control circuit, which comprises a voltage reference circuit. The output end of the voltage reference circuit is connected with the input end of a soft start circuit; the output end of the soft start circuit is connected with the first input end of an error amplifying circuit; the output end of a sampling isolation amplifying circuit is connected with the second input end of the error amplifying circuit; the output end of the error amplifying circuit is connected with the input end of a voltage frequency oscillator circuit; and the output end of the voltage frequency oscillator circuit serves as a frequency output end of the frequency soft start control circuit. Through changing the position and the mechanism of the soft start circuit, the improved soft start circuit can truly achieve the fact that when a power-on signal arrives, the output frequency is gradually increased to the frequency after loop close from 0 frequency, and the power output is from low to high, and thus, soft start power on for the power supply in a frequency modulation mode is realized, impacts on elements of the circuit in the case of power on can be reduced, and the reliability of the power supply is improved.

Description

technical field [0001] The invention relates to the technical field of control circuits of power electronics, in particular to a frequency soft-start control circuit. Background technique [0002] The control circuit of the switching power supply has a very important influence on the power supply. It is the command and control system of the switching power supply. The power supply has power. In order to reduce the stress on the circuit components and improve the reliability of the power supply, most of the power supply control chips are now internal All have a soft start function, so that the power supply with a power control chip can realize the opening of the power supply soft start. [0003] The schematic diagram of the existing frequency soft start control circuit is as follows: figure 1 As shown, when the power-on signal is sent, since the 15V level of the power-on signal is greater than the 7V voltage reference level, the output voltage of the soft-start integral oper...

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Problems solved by technology

[0004] It can be seen that the disadvantage of the existing soft-start control circuit is that the output frequency is not really established from low to high. Before the power ON level is sent, the input voltage of the voltage frequency oscillator is high, and the corresponding output is the highest. frequency, only when the ON signal comes, the output frequency of the oscillator will be reduced. Practice has proved that this soft start circuit can realize the soft start when the power supply is loaded, but cannot realize the soft start when the power supply is no load.

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