Circuit arrangement for a switched-mode power supply

摘要

If a switched-mode power supply is operated in the standby mode, that is to say on a low load, then its output voltage increases in comparison with the output voltage at a higher load. The filter capacitors which are required on the secondary side must therefore be designed for correspondingly high voltages and are thus expensive. In order to avoid this, it is proposed to reduce the regulation voltage at the regulation input of the drive circuit when the load is low. A switching device is described for this purpose, which reduces the regulation voltage as a function of the depletion voltage occurring in the switching transistor.