Patent ID: 7808756
Filing Date: 2010-10-05
Classification: H02M

Abstract:
1. A protection circuit, comprising: a first input terminal; a second input terminal; an output terminal; at least two transistors including a first and a second transistors connected in series with each other and electrically connected between the first input terminal and the output terminal; and a variable voltage source circuit electrically connected with the first input terminal, the second input terminal, the output terminal, and the gates of the first and second transistors, the variable voltage source circuit being operative such that: when a voltage at the first input terminal is higher than a voltage at the second input terminal, and a voltage at the output terminal is higher than the voltage at the second input terminal, the first and second transistors are both ON and the gates of the first and second transistors are substantially at equal voltage level; when the voltage at the first input terminal is higher than a voltage at the second input terminal, and the voltage at the output terminal is lower than the voltage at the second input terminal, the sates of the first and second transistors are substantially at unequal voltage levels and each of the first and second transistors shares a substantial portion of the voltage difference between the first input terminal and the output terminal; and when the voltage at the first input terminal is equal to or smaller than the voltage at the second input terminal, at least one of the first and second transistors is OFF to disconnect the conduction between the first input terminal and the output terminal.