Title :
Transformer saturation and unusual system oscillation in capacitively coupled half-bridge or full-bridge forward converters: causes, analyses, and cures
Author :
Redl, Richard ; Sokal, Nathan O. ; Schaefer, Carl W.
Author_Institution :
Design Autom. Inc., Lexington, MA, USA
Abstract :
In capacitively coupled bridge converters, duty-ratio unbalanced can cause transformer saturation and resulting transistor destruction. Independently, modulation of the transistor storage time by variations of collector current can cause low-frequency system oscillation which leads also to transformer saturation, and additionally causes low-frequency conducted EMI which is difficult to filter. A resistor shunting the coupling capacitor is suggested as a simple but effective cure for both problems. Mathematical analyses for both phenomena, a design procedure for selecting the proper value of shunt resistance, and experimental results that confirm the analyses are presented.
Keywords :
bridge circuits; power convertors; transformers; capacitively coupled bridge converters; coupling capacitor; duty-ratio unbalanced; full-bridge forward converters; half bridge forward convertors; low-frequency conducted EMI; low-frequency system oscillation; power convertors; shunt resistance; transformer saturation; transistor storage time modulation; variations of collector current; Bridge circuits; Capacitors; Circuit faults; Couplings; Design automation; Irrigation; Postal services; Saturation magnetization; Switches; Switching converters;
Conference_Titel :
Power Electronics Specialists Conference, 1988. PESC '88 Record., 19th Annual IEEE
Conference_Location :
Kyoto, Japan
DOI :
10.1109/PESC.1988.18213