Load connection state detection circuit
View Patent ↗This load connection state detection circuit includes a PNP type transistor whose emitter is connected to a power source terminal, a NPN type transistor where the emitter thereof is connected to the power source terminal, the collector thereof is connected to the base of the PNP type transistor, and the base thereof is connected to the collector of the PNP type transistor, and a diode inserted between the collector of the PNP type transistor and an external antenna load, wherein the diode is configured to perform temperature compensation for the base voltage of the NPN type transistor and prevent currents from flowing from the external antenna load to the PNP type transistor and the NPN type transistor.
1. A circuit for detecting a load connection state of a load connected between an output terminal and a ground, the load allowing a direct current to flow therethrough, comprising:
a first switch element having a first end connected to a power source, a second end; and a control end;
a second switch element having a first end connected to the power source or the ground, a second end connected to the control end of the first switch element, and a control end connected to the second end of the first switch element through a first resistor;
a diode provided between the second end of the first switch element and the output terminal, a potential difference between both ends of the diode changing due to a temperature change,
a second resistor connected between the control end of the second switch element and the ground; and
a third resistor connected between the power source and the first end of the first switch element,
wherein the diode performs temperature compensation for a voltage value in the control end of the second switch element while preventing a current from flowing from the output terminal into the first and second switch elements when an external voltage is applied to the output terminal,
and wherein an electric potential applied to the control end of the second switch element is a combined potential including respective electric potentials due to the first and second resistors, a voltage difference between both ends of the third resistor, and an electric potential of the diode.
2. The load connection state detection circuit according to claim 1 , further comprising:
an amplifying circuit having a first input terminal is connected to a first end of the third resistor and a second input terminal connected to a second end of the third resistor, the amplifying circuit amplifying the voltage difference between the first and second ends of the third resistor; and
a fourth resistor connected between the first and second ends of the first switch element,
wherein the first switch element includes a PNP type transistor having an emitter connected to the first end of the third resistor, a collector, and a base,
wherein the second switch element includes an NPN type transistor having a collector connected to the base of the PNP type transistor through a fifth resistor, a base connected to the collector of the PNP type transistor though the first resistor, and
wherein the diode has a cathode connected to the output terminal, and an anode connected to the collector of the PNP type transistor.
3. The load connection state detection circuit according to claim 1 , wherein the load is an antenna circuit.