Load current adjustment method and circuit and switching power supply with the circuit

Abstract

The invention discloses a load current adjustment method and circuit and a switching power supply with the load current adjustment circuit. The adjustment circuit comprises an LDO, a first feedback compensation circuit and a second feedback compensation circuit. After a PWM signal arrives, the second feedback compensation circuit works to output a voltage feedback (VFB) signal to a power conversion circuit in a feedback mode. The power conversion circuit adjusts the voltage VLDO inputted into the LDO to a stable voltage value in the first time period according to the reference voltage signal and a VFB adjustment output voltage Vo. The LDO begins to work after the first time period and adjusts the load current according to a current feedback signal and the PWM signal till the PWM signal ends. The first feedback compensation circuit feeds back a voltage VLDO to the power conversion circuit after the PWM signal ends. The power conversion circuit makes the VLDO decrease to a linear voltage value according to a VLDO control output voltage Vo till a next PWM signal comes. The bandwidth of an adjustment signal for which the technical scheme is suitable is wider, and the technical scheme can be suitable for high frequency adjustment signals.

Description

technical field [0001] The invention relates to the field of electronics, in particular to a load current adjustment method and circuit and a switching power supply with the circuit. Background technique [0002] In the prior art, there are two-stage dimming circuits and single-stage dimming circuits for LED dimming circuits. figure 1 and figure 2 A two-stage LED dimming circuit and a single-stage LED dimming circuit are provided respectively. [0003] see figure 1 , 2 As shown, in the prior art, the output end of the power conversion circuit is connected to the first end of the load LED, the second end of the LED is connected in series with the first power end of the power switch tube, and the second power end of the power switch tube is grounded . Input the pulse width modulation (Pulse Width Modulation, PWM) signal for controlling the current flowing through the LED at the control terminal of the power switch tube, also known as the dimming signal, and input the cur...

AI Technical Summary

Problems solved by technology

[0005] figure 1 , 2 The LED dimming technical solutions shown are all controlled by the power conversion circuit of the switch circuit according to the current feedback signal I LED’ To adjust the load current, the dimming frequency is limited by the bandwidth of flyback and boost power conversion circuits, and is limited by the response speed of circuit devices. The bandwidth of flyback and boost power conversion circuits cannot be made very high. Generally, the flyback frequency Around 100KHz, the bandwidth is generally below 10K, the boost frequency is 200-400KHz, and the bandwidth is below 20K. It can be seen that the dimming frequency in the prior art cannot be made very high, and the bandwidth is relatively narrow

In fact, the frequency of the applicable PWM dimming signal in the prior art is generally limited to about 100Hz-1KHz

It can be seen that when the existing technology is used, the bandwidth of the dimming signal is narrow and the frequency is low, and the LED dimming may not achieve the required effect and cannot meet the high-frequency LED dimming requirements; The optical frequency range is within the audio frequency range, and it is easy to generate noise that may be audible to the human ear during the dimming process

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