Constant current or constant power output control method and charging circuit

Abstract

The invention relates to the technical field of chargers, in particular to a constant current or constant power output control method and a charging circuit. According to the control method, when a fluctuation voltage is accessed to a charger, a main control chip adjusts the duty ratio to control the output of the transformer according to the input voltage detected by an FB pin, so that the fluctuation of the output circuit is reduced; the chip adjusts the duty ratio by adjusting the conduction time and the demagnetization time of a built-in switch tube; particularly, when the input voltage islow voltage, the built-in switch tube is turned on in advance, and the demagnetization time is reduced, so that the duty ratio time is longer, and the current output is relatively stable. The charging circuit uses the control method of the constant output. In the embodiment, the conduction time of the built-in switch, the switching frequency of the built-in switch and the demagnetization time ofthe transformer are adjusted at the same time through the main control chip according to the detected input voltage and output voltage, so that the transformer outputs relatively constant current or power.

Description

technical field [0001] The invention relates to the technical field of charging, in particular to a control method and a charging circuit for constant current or constant power output. Background technique [0002] Since the PSR (primary side feedback) architecture in switching power supplies usually does not enter continuous mode, in order to maintain constant current output, it is necessary to control demagnetization time = oscillation + conduction time. According to the energy conservation law, the energy stored in one switching cycle of the transformer is equal to = 0.5*IPK*IPK*L, IPK is the peak current, L is the inductance, F is the frequency, IPK is fixed, so the demagnetization time is fixed, for example, when the input voltage is 265V high voltage, the time to reach IPK current is relatively short, only by increasing the oscillation time can it reach 1:1 (1:1 in this patent refers to: demagnetization time: oscillation + conduction time) balance point (see figure 2 ...

AI Technical Summary

Problems solved by technology

[0004] Based on the above reasons, the PSR architecture in the current market requires a relatively large filter capacitor to supply power after the AC voltage is rectified. To prevent the input voltage from being lower than a certain voltage, a larger filter capacitor makes the capacitor energy reach 0.5*C*V*V at the moment of power-on. , The surge current usually reaches more than 50A, and a thermal or wire-wound fuse must be added to limit the current

The life of the filter capacitor is limited, that is to say, the life of the switching power supply is completely limited by the life of the capacitor.

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