Control circuit for controlling power transistor, driving circuit, LED lamp system and control method

Abstract

The invention discloses a control circuit for controlling a power transistor, a driving circuit, an LED lamp system and a control method. The control circuit receives an adjusting signal, and the control circuit is used for adjusting the amplitude of a current flowing through the power transistor based on the adjusting signal when a characterization value of the adjusting signal is greater than afirst threshold value; the control circuit is used for adjusting the current flowing time of the power transistor based on the adjusting signal when the characterization value of the adjusting signalis less than a second threshold value, wherein the second threshold is less than or equal to the first threshold. According to the invention, the control precision and efficiency can be improved. Whenthe characterization value (such as the duty ratio) of the adjusting signal (such as the PWM signal) is a smaller value, the control precision is improved; meanwhile, the drive circuit is small in loss and high in efficiency. The invention is applied to an LED drive scheme, so the dimming precision of an LED drive circuit is improved.

Description

technical field [0001] The invention belongs to the technical field of control circuits, and in particular relates to a control circuit, a drive circuit, an LED lamp system and a control method for controlling a power transistor. Background technique [0002] The linear LED driving circuit is gradually accepted by the market due to its simple and convenient design, but there are problems in the prior art. figure 1 It is a circuit schematic diagram of an existing linear LED driving circuit, figure 2 It is a schematic diagram of the relationship between the duty cycle and Io in the existing linear LED drive circuit; please refer to figure 1 , figure 2 In the prior art, a PWM control reference generating unit is used to generate Vref, the sampling voltage and Vref are obtained through an operational amplifier, and a control signal is output to control the current flowing through the transistor Q, thereby realizing dimming of the LED driving circuit. Adjust the current flow...

AI Technical Summary

Problems solved by technology

When the duty cycle D2 is further reduced, the control accuracy of the LED circuit is affected due to the bias at the input terminal of the operational amplifier.

[0003] image 3 It is a schematic diagram of part of the signal waveform of the existing linear LED drive circuit; image 3 It can be seen that the loss flowing through the transistor Q is (Vin-VF)*Io, the loss of the transistor Q is relatively large, and the efficiency of its LED driving circuit is relatively low

[0004] It can be seen that the linear LED drive circuit in the prior art cannot perform precise regulation when the PWM duty cycle is a low value, which affects the dimming accuracy of the LED drive circuit.

In addition, the prior art linear LED drive circuit has relatively low efficiency

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