Patent ID: 9614363
Date: 2017-04-04
CPC Classifications: H02H

Claim:
1. An under voltage protection device electrically connecting with an external voltage source and comprising: a voltage detector comprising a diode, a variable resistor, a first transistor and a fixed-resistance resistor, wherein the diode has an input electrically connecting with the external voltage source and an output, the variable resistor has a first node, a second node and a third node, the first node of the variable resistor electrically connecting with a ground of the under voltage protection device, the third node of the variable resistor electrically connecting with the output of the diode, the first transistor has a collector node electrically connecting with the first node of the variable resistor and the ground, an emitter node and a base node electrically connecting with the second node of the variable resistor, the fixed-resistance resistor has an input electrically connecting with an operation voltage of the under voltage protection device and an output electrically connecting with the emitter node of the first transistor; and a starting unit comprising a second transistor, the second transistor having a source node, a drain node and a gate node, wherein the source node of the second transistor electrically connects with the collector node of the first transistor and the ground, the gate node of the second transistor electrically connects with the output of the fixed-resistance resistor and the emitter node of the first transistor, the drain node of the second transistor electrically connects with the operation voltage of the under voltage protection device, when a voltage of the external voltage source is smaller than a voltage of the diode, a voltage between the emitter node and the collector node is smaller than a threshold voltage present between the gate node of the second transistor and the source node of the second transistor such that the second transistor is turned off and the starting unit is turned off; when the voltage of the external voltage source is larger than the voltage of the diode, the voltage between the emitter node and the collector node is larger than the threshold voltage present between the gate node of the second transistor and the source node of the second transistor such that the second transistor is turned on and the starting unit is turned on.