| 摘要 |
PURPOSE:To prevent malfunction of a load due to an input current and to increase in power consumption and to protect the input circuit and load to a load current exceeding the upper limit value or over by providing a switch means supplying a current to the load only when the input current is less than a threshold value and setting the threshold value to a desired level and a current suppressing means to the load current. CONSTITUTION:When the input current I is a threshold value or below, since the emitter area of a TrQ4 is larger than that of a Q5, a collector current Ic has a relation of Ic4>Ic5. A current equal to the Ic4 flows to a TrQ3 biased by a TrQ2, the collector potential of the TrQ5 rises near the power supply voltage and a TrQ7 keeps the off state. When the current I is increased, the current Ic4 is increased and the voltage drop across a resistor R2 is increased, so long as the current I does not reach the threshold value Ith decided the emitter area ratio (n) of the Trs Q4, Q5 and the resistor R2, the TrQ7 keeps the off-state. When the current I exceeds the value Ith, the relation of Ic4<Ic5 is obtained, the collector potential of the TrQ5 is lowered and the TrQ7 is turned on. When the current I is increased further, the collector current of the TrQ6 is increased, the Ic4, Ic5 are decreased and then the current I is decreased. Further, the relation of Ic4>Ic5 is obtained to limit the load current.
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