SINGLE CLOCK CONDUCTION TYPE CONVERTER FOR GENERATING OUTPUT DC VOLTAGE ISOLATED IN DC

摘要

1. A single-ended forward converter with a pulse-width controlled semiconductor switch (41) in the converter main circuit, and with a power transformer (31) having a plurality of secondary windings (311, 312) for the generation of electrically isolated d.c. output voltages, where at least one output circuit of the single-ended forward converter contains a transistor switch (42) which is pulse-width controlled in dependence upon the output voltage (U22) of this output circuit and which possesses its own auxiliary control circuit whose output pulses occur within the output pulses of the semiconductor switch (41) in the main circuit and which is rendered conductive at the same time as the control transistor located in the converter main circuit, the transistor (42) being arranged in an output circuit that is rendered inoperative by short-circuiting a winding (71) of a pulse-control transformer (7) in dependence upon the output voltage (U22) of the corresponding output circuit, the pulse transformer (7) being preceded by a switch-on device and a switch-off device and the emitter-collector path of a transistor (43) of the switch-off device arranged parallel to a winding (71) of the pulse transformer (7), characterised in that the switch-on device is formed by a series arrangement of a resistor (12) and a diode (57), and that a winding (74) of the pulse transformer is connected via the series arrangement (12, 57) to a separate switch-on winding (311) of the power transformer (31), and that the switch-off device contains a threshold-value switch (81) having an open collector output, whose first input (+) is supplied with a control value which is dependent upon the output voltage and whose other input (-) is supplied with a comparison value (URef ) and which has its output connected via a timer circuit in the form of a mono-stable flip-flop stage which contains a capacitor (21) and a charge resistor (13 ... 15), to that transistor (43) of the switch-off device whose emitter-collector path is arranged parallel to a separate switch-off winding (71) of the pulse transformer (7).