| 摘要 |
<p>PURPOSE:To protect an inverter from overcurrent, by detecting abnormal voltage increase and bringing an overcurrent protection circuit into apparent overcurrent detecting state. CONSTITUTION:When input voltage of an inverter 3 increases and the voltage across a capacitor C1 exceeds 120% of normal level, the voltage is divided through resistors R16, R17 and the voltage across the resistor R16 increases. Since the resistors R16, R6 are common at plus side, base voltage of transistor Q7 lowers and the transistor Q7 enters into ON state. Consequently, resistor R4 is shortcircuited and the potential at inverted input terminal (-) of an operational amplifier OPA1 lowers. When the voltage increases furthermore, the transistor Q7 serves as a diode and brings the voltage at the inverted input terminal (-) of the operational amplifier OPA1 to zero volt. At this time, non- inverted terminal (+) of the operational amplifier OPA1 is positive fed back through a circuit of C5, R7, R5, and the output of the operational amplifier OPA1 is brought to high level during an interval when it is lowered to zero volt. Consequently, no drive signal is fed from a drover 7, and the inverter 3 is disabled.</p> |
