Protection circuit for DC converter - has monostable to suppress switching transistor drive and circuit to gradually restart converter after short has cleared

摘要

The protection circuit has a monostable multivibrator that passes over into its unstable state for a given time when the electrical energy in the primary of the output transformer exceeds a given limit. In this unstable state the multivibrator suppresses the generation of drive pulses to the base of a switching transistor. A circuit gradually increases the length of the base drive pulses from zero at the end of the multivibrator's unstable state over a time interval longer than the spacing between consecutive base drive pulses. The protection circuit automatically restarts the converter once the condition causing overload, e.g. a short circuit, has disappeared.