Patent ID: 8089264

Claim:
A voltage measuring circuit, comprising: an under-voltage measuring circuit, comprising a first resistor, a second resistor, a first voltage comparator, a first zener diode, and a first light emitting diode, wherein a cathode of the first zener diode is connected to a power source via a third resistor, an anode of the first zener diode is grounded, an inverting input of the first voltage comparator is connected to the cathode of the first zener diode, a non-inverting input of the first voltage comparator is connected to the power source via the first resistor and grounded via the second resistor, an output of the first voltage comparator is connected to a cathode of the first light emitting diode, an anode of the first light emitting diode is connected to the power source, wherein a relationship of a stable voltage V-dw 1 of the first zener diode, a lower limit V-min of the power source, a resistance R 1 of the first resistor, and a resistance R 2 of the second resistor is that V-dw 1 =V-min×R 2 /(R 1 +R 2 ); and an over-voltage measuring circuit, wherein the over-voltage measuring circuit comprises a fourth resistor, a fifth resistor, a second voltage comparator, a second zener diode, and a second light emitting diode, a cathode of the second zener diode is connected to the power source via a sixth resistor, an anode of the second zener diode is grounded, a non-inverting input of the second voltage comparator is connected to the cathode of the second zener diode, an inverting input of the second voltage comparator is connected to the power source via the fourth resistor and grounded via the fifth resistor, an output of the second voltage comparator is connected to a cathode of the second light emitting diode, an anode of the second light emitting diode is connected to the power source, wherein a relationship of stable voltage V-dw 2 of the second zener diode, an upper limit V-max of the power source, a resistance R 4 of the fourth resistor, and a resistance R 5 of the fifth resistor is that V-dw 2 =V-max×R 5 /(R 4 +R 5 ).