POWER SUPPLY CIRCUIT
FIG4 is a circuit diagram showing an example of a step-down chopper shown in FIG2 for which commonly-used surge countermeasures are taken
FIG4 is a circuit diagram showing an example of a step-down chopper shown in FIG2 for which commonly-used surge countermeasures are taken. As shown in FIG4, Zener diode ZD1 is provided in parallel with capacitor C1. Zener diode ZD1 should not operate during the normal operation of power supply circuit 10A. Thus, the operating voltage of Zener diode ZD1 should be higher than the design value of the input voltage. On the other hand, in order to protect transistor TR1, the operating voltage of Zener diode ZD1 should be lower than the rated voltage of transistor TR1. From a point of view of the efficiency of power supply circuit 10A, it is desirable to reduce the loss during switching of transistor TR1 as much as possible. Generally, in the transistor with low switching loss, the rated voltage is also low. However, when the rated voltage of transistor TR1 is low, the difference between the input voltage during the normal operation of power supply circuit 10A and the rated voltage of transistor TR1 is relatively small. For example, when the voltage of AC power supply 20 is 100 VAC, a peak voltage Vpeak (and the voltage after rectification) is 141 V. Thus, the input voltage during the normal operation of power supply circuit 10A (voltage Vi) is 141 V. In the case of power supply circuit 10A shown in FIG4, the operating voltage of Zener diode ZD1 should be 180 V higher than 141 V.
circuit diagram
11
surge protection circuit
20
AC power supply
['1. A power supply circuit (10) comprising: a coil (L1) having a first end that receives an input voltage and a second end; a switching element (TR1) connected to the second end of the coil (L1); a first capacitor (C1) connected to the second end of the coil (L1); and a surge protection circuit (11) connected to the second end of the coil (L1) in parallel with the first capacitor (C1), the surge protection circuit (11) including a diode, a second capacitor (C2), and a resistance (R1), the diode, the second capacitor (C2), and the resistance (R1) being connected in series to the second end of the coil (L1).']