Power supply control apparatus
In a power supply control apparatus, if a switching signal input from a microcomputer to a control circuit instructs switching on of a semiconductor switch, when an input voltage that is input to the drain of the semiconductor switch is higher than or equal to a predetermined voltage, the control circuit drives a charging circuit. The charging circuit charges a capacitor (Cs) via a diode (D 1 ). Accordingly, a voltage at the gate of the semiconductor switch taking a potential at the source of the semiconductor switch as a reference becomes higher than or equal to a predetermined voltage, and thus the semiconductor switch is switched on. While driving the charging circuit, the control circuit keeps driving the charging circuit even if the input voltage becomes lower than the predetermined voltage.
1. A power supply control apparatus including a semiconductor switch that is provided in a current path and is switched on if a voltage at its control terminal becomes higher than or equal to a predetermined voltage, whereas is switched off if the voltage at the control terminal becomes lower than the predetermined voltage, the power supply control apparatus being configured to control power supply through the current path by switching the semiconductor switch on or off, the power supply control apparatus comprising:
a capacitor whose one end is connected to the control terminal;
a charging circuit configured to charge the capacitor;
a diode configured to prevent a current from flowing through the charging circuit from the capacitor;
an input-voltage detection unit configured to detect an input voltage that is input to a current input terminal in the semiconductor switch;
an input unit to which a switching signal instructing switching on or off of the semiconductor switch is input; and
a driving unit configured to, if the switching signal input to the input unit instructs switching on of the semiconductor switch, drive the charging circuit when the voltage that the input-voltage detection unit has detected is higher than or equal to an input-voltage threshold value,
wherein, while operating the charging circuit, the driving unit keeps driving the charging circuit even if the voltage that the input-voltage detection unit has detected becomes lower than the input-voltage threshold value.
2. The power supply control apparatus according to claim 1 , comprising:
a terminal-to-terminal voltage detection unit configured to detect a voltage between the input terminal of the semiconductor switch and a current output terminal in the semiconductor switch; and
a discharging circuit configured to discharge power that the capacitor has accumulated,
wherein, if the driving unit drives the charging circuit, when the voltage that the input-voltage detection unit has detected becomes lower than the input-voltage threshold value and the voltage that the terminal-to-terminal voltage detection unit has detected becomes higher than or equal to a terminal-to-terminal voltage threshold value, the driving unit stops operation of the charging circuit and drives the discharging circuit.
3. The power supply control apparatus according to claim 1 , comprising:
a terminal-to-terminal voltage detection unit configured to detect a voltage between the input terminal of the semiconductor switch and a current output terminal in the semiconductor switch; and
a discharging circuit configured to discharge power that the capacitor has accumulated,
wherein, if the driving unit drives the charging circuit and a voltage that the terminal-to-terminal voltage detection unit has detected is higher than or equal to a terminal-to-terminal voltage threshold value continues for a predetermined time period or longer, the driving unit stops operation of the charging circuit and drives the discharging circuit.
4. The power supply control apparatus according to claim 2 , comprising:
an output circuit configured to output a voltage within a predetermined range depending on a current flowing through the current path; and
an adjusting unit configured to, if the driving unit stops the operation of the charging circuit and drives the discharging circuit, adjust the voltage at a voltage output terminal from which the output circuit outputs the voltage to a voltage out of the predetermined range.