A constant current and constant voltage control method and circuit for primary side feedback

Abstract

The invention provides a constant current and constant voltage control method and circuit for primary side feedback. The circuit comprises a demagnetizing time converter which is used for detecting demagnetizing time and converting the demagnetizing time into demagnetizing time voltage signals; a frequency adjuster used for generating constant voltage clock frequency control signals; an oscillator which generates sawtooth signals under the control of the constant voltage clock frequency control signals, and generates constant current clock start signals by comparing the values of the sawtooth signals and the values of the demagnetizing time voltage signals or generates constant voltage clock start signals by comparing the values of the sawtooth signals and the values of preset constant voltage and constant current dividing voltage. A novel method is used for generating the CC / CV start clock signals and one start clock generator can be shared, so that the problem of time sequence competition possibly caused by two paths of signals is effectively solved; an oblique wave generating circuit is removed so that the cost is reduced; the generation of high frequency signals is not needed, so that the risk of a parasitic effect is prevented.

Description

technical field [0001] The invention belongs to the technical field of electronic circuits, and relates to a constant current and constant voltage control method and system, in particular to a constant current and constant voltage control method and circuit for primary side feedback. Background technique [0002] In the existing circuit implementation of the primary side feedback control chip, since the constant current or constant voltage control method is relatively complicated, the usual practice is to use two different circuits to process the constant current circuit and the constant voltage circuit respectively. [0003] see figure 1 As shown, the primary side feedback constant current constant voltage controller 100 includes: a demagnetization time (Tdis) detector 101, which is used to detect the demagnetization time and generate a signal for judging CC / CV (constant current / constant voltage); an oscillator 102 , used to generate clock start signal; line compensation g...

AI Technical Summary

Problems solved by technology

[0026] In view of the shortcomings of the prior art described above, the purpose of the present invention is to provide a constant current and constant voltage control method and circuit for primary side feedback, which is used to solve the problem of constant current and constant voltage control in the existing primary side feedback control technology. Implemented in two independent ways, there are timing competition risks and parasitic effects, resulting in complex circuits and high costs.

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