Method and circuit for accurately controlling switch power supply output current

Abstract

This invention discloses a kind of method and circuit of precisely controlling to switch power supply to output current. This method uses switching power supply to detect and get the average current flowing from voltage transformer primary coil or inductance element during switching on the switch element. It also uses switching power supply to detect and get the time, which is either from switching off the switch element to the current of voltage transformer secondary coil or inductance attenuates to zero, or from switching off the switch element to the current of voltage transformer secondary coil or inductance does not attenuate to zero but the period of switch element switching off has finished; then, based on the detected times and average current, as well as their equivalent transformed signals, the said output current is controlled by switching power supply; in addition, it also provides a kind of circuit. It concludes: a current detector used for detecting the said average current; a demagnetizing time detector used for detecting the said time; a multiplier which gets average current, times or their equivalent transformed signals. The output of multiplier controls and outputs current.

Description

technical field [0001] The invention belongs to switching power supply technology, in particular to a precise control method and circuit for switching power supply output current. Background technique [0002] In switching power supply technology, not only the output voltage needs to be controlled, but also the output current is often required to be controlled, for example, the output current is required to be constant. At present, in the application of flyback switching power supply (flyback AC-DC converter), the most common method is to connect a resistor in series with the secondary output of the transformer to detect the output current, and control the voltage at both ends of the series resistor to control the output voltage. current. Since the control signal must be fed back to the primary control chip, it is necessary to increase the isolation device between the primary and secondary stages, so that although the output current is well controlled, it also greatly incre...

AI Technical Summary

Problems solved by technology

[0019] Since Equation 3 is valid only if the transformer works in DCM (Discontinuous Current Mode), this requires that the switching power supply using this method cannot enter the working mode of CCM (Continuous Mode of Operation), which greatly limits the use of switching power supply ;In addition, the input power and the maximum input current have a square relationship, not a linear relationship, which requires a square transformation inside the switching power supply, which will bring more precision loss

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