| 摘要 |
PROBLEM TO BE SOLVED: To prevent a device from being damaged by speedily disallowing a current to flow to primary winding when a resistance for current detection short-circuits.SOLUTION: A primary-side control circuit of an insulation type DC power supply unit having a transformer is provided with: a voltage detection circuit which imparts a timing when a switching element is turned ON based upon a voltage induced across auxiliary winding; a current detection circuit which imparts a timing when the switching element is turned OFF based upon a current flowing to the primary winding; a signal generation circuit which generates an ON and an OFF control signal according to output signals of the current detection circuit and voltage detection circuit; a first timer circuit which is actuated at the ON timing of the switching element to start a clocking operation for an ON time of the switching element, and a second timer circuit which is actuated as the first timer circuit times up to start a clocking operation. The primary-side control circuit is configured not to generate the signal turning ON the switching element when the second timer circuit clocks an allowed demagnetization time and times up.SELECTED DRAWING: Figure 2 |
