An Adaptive Slope Compensation Circuit and Its Application

To solve the over-compensation problem in the current mode PWM switch power, a new adaptive slope compensation circuit is proposed in this paper. In the circuit, the difference between the output and input voltage is positively correlated with the duty cycle of switch signal, which is used to generate the control signal varying with the duty ratio. The control signal is used to control the gate voltage of MOS operating in linear region, which changes the linear drain-source resistance. With clamping circuit, a proportional ramp voltage with controllable slope is produced and amplified for compensation system by two stage amplifier. This compensation voltage is almost ideal, which can reduce the negative effect of over-compensation farthest. This circuit is applied to an LED driver IC and simulated in Cadence with CSMC 0.5um BiCMOS library. The results show that the boost driver circuit using adaptive compensation has about 28% dynamic response time reducing compared with the settled slope compensation. Therefore, the proposed compensation circuit can improve system’s dynamic responsibility effectively.