| 摘要 |
A power supply unit is arranged to receive ac power (VIN) and to output a number of different do output voltages (V1 ,V2). The unit includes a power transformer (T1) and a feedback control device (8) arranged to limit the primary side current in response to high currents to the lower rated dc output (V2). The current to output (V2) is sensed by a bipolar transistor (Q2) connected so that, in normal conditions, it is switched off. If the current supplied to output (V2) is too high, the transistor (Q2) switches on and supplies current to the feedback control (8) whereby regulation of the output voltage (V2) is achieved. The transistor (Q2) can be arranged in a single package with a diode (D2) provided in the rectifying circuit for the lower rated output (V2). This protects the circuit against variations due to differences in temperature between the diode and the transistor. The packaged arrangement of these components can be used as a current monitoring device in other contexts. |
