Patent ID: 7474145
Filing Date: 2009-01-06
Classification: G05F

Abstract:
1. A constant current circuit, comprising: first and second depression type MOS transistors having drains connected to a high electric potential side; and first, second, and third enhancement type MOS transistors having sources connected to a low electric potential side; wherein a source of the first depression type MOS transistor and a drain of the first enhancement type MOS transistor are connected so that a first connection is formed, a gate of the first depression type MOS transistor and a gate of the first enhancement type MOS transistor are connected so that a second connection is formed; the second connection and the first connection are connected so that a third connection is formed; a source of the second depression type MOS transistor and a drain of the second enhancement type MOS transistor are connected via a resistance so that a fourth connection is formed; a gate of the second depression type MOS transistor and a gate of the second enhancement type MOS transistor are connected so that a fifth connection is formed; the fifth connection and the first connection are connected so that a sixth connection is formed; a gate of the third enhancement type MOS transistor is connected to the fourth connection between the drain of the second enhanced type MOS transistor and the resistance so that a seventh connection is formed; and a drain of the third enhancement type MOS transistor is an output end of the constant current circuit.