Patent EP-0022380-A1 (EP)
Inventor: FACON MICHEL
IPC: H04N3/185
Filed: 1980-05-12
Abstract: 1. A chopping power-supply device combined with a line-scanning circuit in a televison receiver, which it supplies, and the output stage (10) of which comprises, more specifically, a controlled bidirectional scanning switch (11) and, mounted in parallel with this switch, a series assembly comprising a storage condenser (15) and a first winding (21) of a line transformer (20) and a return condenser (14), the device comprising a chopping circuit (30) which more specifically comprises, connected in series between the poles (6, 7) of DC supply source (5), a second winding (22) of the line transformer (20), and a controlled bidirectional chopping switch (32), energy transfer being effected by means of the first and second windings (21, 22) and regulation being effected by variable phase displacement between the respective chopping times of the scanning (11) and chopping (32) switches, normally working at constant cyclic ratios and frequency, in relation to an electrical quantity derived from the voltage at the terminals of the storage condenser (15) and obtained by means of a variable delay generator (40) supplied by a third winding (23) of the line transformer (20), which supplies line-return pulses, the chopping switch (32) comprising a transistor (320) and a diode (321), mounted in parallel and in such a way as to conduct in opposite directions, characterized by the fact that the chopping circuit (30) further comprises an additional chopping inductance (31), inserted in series between the second winding (22) and the chopping switch (32), a turning condenser (33) being connected in parallel with this switch, in order to form a resonance circuit with the chopping inductance (31), and by the fact that it is combined with a control and startup circuit ensuring self-contained startup when switched on, thereupon supplying the base of the chopping transistor (320), and comprising a reaction winding (35) wound on the core (36) of the chopping inductance (31), in such a way as to form another transformer (37) and with one terminal connected to the junction (300) between the transistor emitter (320) and the anode of the diode (321), and a second terminal connected by means comprising in particular a current-limiting resistor (38) to the base of transistor (320), in order to polarize it, by means of a voltage in phase apposition with its collector voltage, a thyristor (52), the cathode of which is connected to the negative pole (7) of the supply source (5), and connected, by means of a protective resistor (34), to the junction (300) of the emitter of transistor (320) and the anode of diode (321), which is connected in turn to the gate of thyristor (52) by means of a gate resistor (53), and the anode of which is connected to the said base, more specifically by means of another DC voltage source (50), designed to polarize the base-emitter junction of transistor (320) in reverse, during activation of thyristor (52), which is tripped at startup or in the absence of line-return pulses by a drop in voltage at the terminals of the protective resistor (34), caused by the lineally increasing current in the chopping inductance (31) during conduction of transistor (320), which is then polarized by means of a startup resistor (301) connecting its base to the positive pole (6) of the power source (5), and by the fact that, in normal operation, starting of the thyristor (52) is controlled by delayed pulses, supplied by the output (47) of the generator (40) connected to the gate by means of a connection condenser (54).