| 摘要 |
PURPOSE: A protection circuit for low input voltage is provided to prevent power supply from being damaged due to the high input current by cutting off the power supply at set level when low input voltage is applied. CONSTITUTION: A protection circuit for low input voltage includes coils(L2,L3), a diode(D1), a PWM circuit(100), an FET(Q3) for switching a power factor and a capacitor(C3). An auxiliary power supply includes a diode(D1) and a coil(L1) at the input terminal. An auxiliary power source circuit supplies constant power by a zener diode(D2) as an input voltage passed through the auxiliary power supply is divided by resists(R1,R2). A constant power source supply inputs the constant voltage by an FET(Q1), a zener diode(D3), and a capacitor(C1). A low voltage sensor detects a low voltage by the output of the constant power source supply. A low voltage on-off circuit controls the PWM circuit(100) by the on-off capacitor(C2) of the FET(Q2).
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