Load drive circuit having low voltage detector

A load drive circuit comprising:

• a charge pump circuit for receiving a power voltage from a power source, increasing the power voltage and outputting an output voltage;
• a low voltage detecting circuit for receiving the output voltage from said charge pump circuit and outputting an output signal to indicate whether the output voltage of the charge pump circuit is in a low voltage state or high voltage state, wherein said low voltage state is for indicating the output voltage of said charge pump circuit is lower than a predetermined level;
• and
• a switch circuit located in a power supply path for connecting said power source and a load for setting said power supply path to an opening state or a closing state based on a drive command signal, the output signal from said low voltage detecting circuit and the output voltage of said charge pump circuit;
• wherein said switch circuit is constructed such that said switch circuit sets said power supply path to the opening state irrespective of said drive command signal in a period in which said low voltage detecting circuit detects said low voltage state, and
• said low voltage detecting circuit includes a constant current diode voltage lowering circuit as a voltage detection circuit for detecting the output voltage of said charge pump circuit and outputting a detected voltage, a reference voltage generating circuit for generating a reference voltage corresponding to said predetermined level, and a comparing circuit for comparing said detected voltage and said reference voltage.

A load drive circuit comprising:

• a charge pump circuit for receiving a power voltage from a power source, increasing the power voltage and outputting an output voltage;
• a low voltage detecting circuit for receiving the output voltage from said charge pump circuit and outputting an output signal to indicate whether the output voltage of the charge pump circuit is in a low voltage state or a high voltage state, wherein said low voltage state is for indicating the output voltage of said charge pump circuit is lower than a predetermined level;
• a switch circuit located in a power supply path for connecting said power source and a load for setting said power supply path to an opening state or a closing state based on a drive command signal, the output signal from said low voltage detecting circuit and the output voltage of said charge pump circuit, wherein the switch circuit is constructed by a switching element located in said power supply path and an element drive circuit for switchably opening and closing of said switching element based on said drive command signal;
• and
• a power supply circuit for receiving the power voltage from the power source and supplying control voltages to the element drive circuit of the switch circuit and the low voltage detecting circuit;
• wherein said switch circuit sets said power supply path to the opening state irrespective of said drive command signal in a period in which said low voltage detecting circuit detects said low voltage state.

A method for driving a load connected to a battery through a switch circuit, the method comprising:

• increasing a voltage of the battery by a charge pump circuit and outputting an increased output voltage;
• detecting whether the increased output voltage of the charge pump circuit is in a low voltage state or a high voltage state relative to a predetermined voltage level;
• and
• controlling an on-off switching state of the switch circuit in response to both a drive command signal for the switch circuit and an output signal generated based on the detecting whether the increased output voltage of the charge pump circuit is in the low voltage state or the high voltage state relative to the predetermined voltage level;
• wherein the controlling an on-off state of the switch circuit forcibly turns off the switch circuit irrespective of the drive command signal, while the output signal generated based on the detecting whether the increased output voltage of the charge pump circuit is in the low voltage state or the high voltage state relative to the predetermined voltage level indicates that the increased output voltage is in the low voltage state.