| 摘要 |
PROBLEM TO BE SOLVED: To provide a switching power unit which protects a transistor from damage caused by overcurrent without using the transistor of more than a necessary capacity. SOLUTION: When it is detected that collector current of a transistor 11 which constitutes a main switching transistor circuit 10 increases, a transistor 22 immediately bypasses base current of the transistor 11 and cuts off the collector current of the transistor 11. Because of this, the transistor 11 can be protected from damage which is caused by overcurrent, and when a load short circuit occurs, cutting off the collector current of the transistor 11 can prevent the transistor from being damaged by turning on a diode 31. Therefore, overcurrent does not flow into the transistor 11, and it is possible to make a device small because the capacity of the transistor does not need margin any more. |
