Circuit arrangement for the variable supply of an ohmic load from an AC network

摘要

The invention relates to a circuit arrangement for the variable supply of an ohmic load from an AC network having at least one switched-mode power supply. It is known to drive a semiconductor switch of a switched-mode power supply in such a way that a sinusoidal network current is created and the load current or a coil current, respectively, flows continuously or has gaps, the immediately beginning gapping operation exhibiting a best compromise with respect to losses etc. Depending on the switch-on duration, the corresponding switch-off duration is then, however, to be determined. For this purpose, the load current must be detected, and when it becomes zero, a pulse must be generated for the semiconductor switch to be switched back on, which involves considerable difficulties, for which reason the times of switching on and off of currents and voltages in the switched-mode power supply are controlled for the entire output power range to be set, such that, with inclusion of the power-dependent impedance of the load, a triangular current is produced, whereby a sinusoidal network current is guaranteed, low losses and reduced high-frequency interference levels are achieved and, above a specific output power, the load can be connected directly onto the AC voltage network.