An Adaptive High Precision Constant Current Circuit and Switching Power Supply

Abstract

The invention discloses a self-adaptive high-precision constant current circuit, which comprises a sampling hold circuit, a peak value calculation circuit, a demagnetization time detection circuit, a comparator, a leading-edge blanking circuit and an RS trigger, wherein an input end of the sampling hold circuit is connected with a CS end, and an output end of the sampling hold circuit is connected with a first input end of the peak value calculation circuit; an input end of the demagnetization time detection circuit is connected with an FB end, and an output end of the demagnetization time detection circuit is connected with a second input end of the peak value calculation circuit; an output end of the peak value calculation circuit is connected with a first input end of the comparator; an input end of the leading-edge blanking circuit is connected with the CS end, and an output end of the leading-edge blanking circuit is connected with a second input end of the comparator; an output end of the comparator is connected with an R end of the RS trigger; and an output end of the RS trigger is used for outputting a PWM signal controlling a power tube to switch on or off, and an S end of the RS trigger is connected with a PWM_ON signal. The self-adaptive high-precision constant current circuit is capable of maintaining high-precision constant current output.

Description

technical field [0001] The invention relates to the technical field of circuit design, in particular to an adaptive high-precision constant current circuit and a switching power supply. Background technique [0002] With the increasing demand for switching power supplies, the requirements for the function and performance of the main control chip of the power supply are also getting higher and higher. In some special applications, the performance requirements for the main control chip of the power supply are higher; for example, in LED drivers , it is required that the output current has high precision under the condition of full-range AC input (90V / 60Hz~264V / 50Hz). To output high-precision current under full-range AC input conditions, the difference in peak current flowing through the primary inductance of the transformer is required to be as small as possible. For the convenience of description, assume that the system works in discontinuous mode (DCM). In an ideal state, a...

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Problems solved by technology

[0009] It can be seen from formula (4) that the output current is affected by the input voltage, primary inductance, and system delay, and the deviation of system delay is not quantifiable for different power main control chips, so it is impossible to control the accuracy of the system and it is difficult to maintain High precision constant current output

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