| 摘要 |
<p>The present invention relates to an electronic control circuit (10) that detects a short-circuit or excess current condition and, in response thereto, cuts off the output current from the system power supply. The circuit is disposed between a system power supply (20) and a load device (22). An output transistor (Q1) is connected between the system power supply and the load device to control the level of current supplied to the load device, including cutting off the current supply entirely in case of a short-circuit or excess current condition. The output transistor is controlled by a pre-drive transistor (Q3) which, in combination with pre-drive resistors, provides a control signal to the output transistor to control the level of output current supplied to the load device. The control signal produced by the pre-drive transistor is dependent upon the output of an operational amplifier (U1) that compares the output potential to a pre-determined reference voltage to determine if the output potential has reached a stable level. In the event of a short-circuit or excess current condition, a switch network (18), consisting of a switch transistor (Q2), a resistor (R10), and two diodes (D1,D2) in the preferred embodiment, deactivates the pre-drive transistor, which in turn deactivates the output transistor. The output transistor cuts off the output current from the system power supply, thereby protecting the system power supply from possible damage. <IMAGE></p> |
