POWER SUPPLY CIRCUIT
FIG3 is a diagram showing a schematic waveform of a surge voltage that may occur in the power supply circuit shown in FIG1
At the start-up of power supply circuit 10A, a current i1 flows through coil L1 for charging capacitor C1. Current i1 in this case is an instantaneously high current (that is, an inrush current). Since transistor TR1 is off, current i1 flows into capacitor C1. When current i1 instantaneously increases, the voltage on coil L1, that is, the voltage across capacitor C1 (voltage Vi), suddenly rises as shown in FIG3.
diagram
10
power supply circuit
['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).']