Load control device having multiple terminals and a clamp circuit connected therebetween
Disconnection of a circulation path through which a circulation current flows is detected while suppressing an increase in circuit scale. A battery monitoring device includes switching circuits that control currents flowing through coils of main contactors by being controlled to be turned on and off, freewheeling diodes that are connected to the coils of the main contactors to form circulation paths for circulating the currents, and a control unit. The control unit measures output voltages of the freewheeling diodes at an input terminal, and detects the disconnection of the circulation paths based on the output voltages of the freewheeling diodes.
1. A load control device comprising:
a switching circuit that controls a current flowing through an inductive load by being controlled to be turned on and off;
a freewheeling diode that is connected to the load to form a circulation path for circulating the current;
a first voltage measurement unit that measures an output voltage of the freewheeling diode;
a control unit that detects disconnection of the circulation path based on the output voltage of the freewheeling diode measured by the first voltage measurement unit,
a clamp circuit that clamps a voltage applied to the switching circuit from the load to a predetermined clamp voltage or less, wherein
the clamp circuit is connected to an input side of the freewheeling diode,
the clamp voltage is a voltage higher than the output voltage of the freewheeling diode measured by the first voltage measurement unit when the circulation pass is not disconnected,
the switching circuit includes a first terminal to which a drive signal for controlling on and off of the switching circuit is input and a second terminal to which the load and the freewheeling diode are connected, and
the clamp circuit is connected between the first terminal and the second terminal.
2. The load control device according to claim 1 , wherein
the switching circuit and the freewheeling diode are provided for each of a plurality of the loads,
outputs of a plurality of the freewheeling diodes are electrically connected to each other at a predetermined connection point, and
the first voltage measurement unit measures output voltages of the plurality of freewheeling diodes by measuring voltages at the connection point.
3. The load control device according to claim 1 , further comprising a second voltage measurement unit that measures a terminal voltage of the load.
4. The load control device according to claim 1 , wherein
the control unit outputs, to the switching circuit, a drive signal for controlling the on and off of the switching circuit, and
when the disconnection of the circulation path is detected, the control unit changes the drive signal.
5. The load control device according to claim 4 , wherein
the control unit outputs, as the drive signal, a PWM signal for performing PWM control of the switching circuit, and
when the disconnection of the circulation path is detected, the control unit changes a duty of the PWM signal.
6. The load control device according to claim 1 , wherein
the load is a coil that changes a switching state of a contactor for connecting a battery to an operating system that operates by using a power supplied from the battery, and
the control unit has a battery monitoring function of monitoring the battery.