Abstract
The change of the over-current protection point of the power switches, caused by slope compensation, is analyzed in detail. It is discovered that the peak current protecting value increases as the duty cycle decreases. As a result, the safety operation of the switches is damaged greatly. A novel solution to improve over-current protection with constant peak current limitation is proposed by inducing synchronous slope compensation into the current limit function instead of the original constant voltage. The design principle and method of the protection circuit based on a UC3846 PWM controller for the interleaved dual-forward converter is presented. Experimental results are given to verify the analysis.
Highlights
The control method for high-frequency DC-DC converters can generally be put into two categories: voltagecontrolled converters and current-controlled converters
A novel solution to improve over-current protection with constant peak current limitation is proposed by inducing synchronous slope compensation into the current limit function instead of the original constant voltage
What we limit is the sampled current value after slope compensation, and the actual peak current limiting value should be calculated by expression (5)
Summary
The control method for high-frequency DC-DC converters can generally be put into two categories: voltagecontrolled converters and current-controlled converters. Peak-current regulation is widely applied because it has the following advantages [2]: perfect linear control and fast dynamic response, the cancellation of the second-order pole and the attainment of the first-order system, and the simplification of over-load and short-circuit protection due to pulse-by-pulse current limiting. Slope compensation is needed to achieve a state system when duty cycle D > 0.5 [3]. The introduction of slope compensation will cause a limited amount of current through the switches to lessen as the duty cycle decreases, so the rated voltage of switches cannot be employed sufficiently. The proposed method is to combine the slope compensation signal with the current-limiting circuit in order to achieve constant peak current limiting value in the wide range of the duty cycle
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