P1-4-Ch10-带隔离DC.ppt

* 10-4-4 Push-Pull Converter voi 0 0 t t N 2 N 1 d U on t D Ts/2 iL Io Vo (a) (b) i + Vd - R T + Vo - 1 D 2 D L N1 N2 T1 L I o + - oi u T2 N1 N2 In the condition of steady-state: * 10-4-4 Push-Pull Converter voi 0 0 t t N 2 N 1 d U on t D Ts/2 iL Io Vo (a) (b) i + Vd - R T + Vo - 1 D 2 D L N1 N2 T1 L I o + - oi u T2 N1 N2 * 10-4-4 Push-Pull Converter Noting: in practical circuit, the anti-parallel diodes are needed to provide a path for the current required due to leakage flux of the transformer. Due to a slight and unavoidable difference in the switching times of the two switches T1 and T2, there is always an imbalance between the peak values of the two switch current. + Vd - R T + Vo - 1 D 2 D L N1 N2 T1 L I o + - oi u T2 N1 N2 * 3 An practical Push-Pull dc-dc supply 10-4-4 Push-Pull Converter * 10-4-5 Half-Bridge Converter 10-4-5 Half-Bridge Converter Half-Bridge converter requires two split capacitors Ca and Cb to form a dc input mid-point. The switches Q1 and Q2 are turned on alternatively, each for an interval ton. 1 converter circuit * 10-4-5 Half-Bridge Converter (a) voi 0 0 t t N2Vd/2N1 on t D Ts/2 iL Io Vo (b) R 1 D 2 D L C1 C2 L i I o Vd/2 + v1 - + - oi u + Vd - + Vo - N1 N2 T1 T2 N2 2 Operation principle (Similar to that of push-pull converter) (1) When T1 is on and T2 is off (0tton), D1 conducts and D2 gets reverse biased. iL through D1 increase linearly. * 10-4-5 Half-Bridge Converter (a) voi 0 0 t t N2Vd/2N1 on t D Ts/2 iL Io Vo (b) R 1 D 2 D L C1 C2 L i I o Vd/2 + v1 - + - oi u + Vd - + Vo - N1 N2 T1 T2 N2 (2) When T1 is off and T2 is on (0tton), D1 gets reverse biased and D2 conducts. iL through D2 increase linearly. * 10-4-5 Half-Bridge Converter (a) voi 0 0 t t N2Vd/2N1 on t D Ts/2 iL Io Vo (b) R 1 D 2 D L C1 C2 L i I o Vd/2 + v1 - + - oi u + Vd - + Vo - N1 N2 T1 T2 N2 (3) When T1 and T2 are off (tontton+Δ), D1 and D2 conduct. iL through D1 and D2 decrease linearly. * 10-4-5 Half-Bridge Converter (a) voi 0 0 t t N2Vd/2N1 on t D T