Constant-current power supply circuit and switching power supply circuit using depletion-mode MOS (Metal Oxide Semiconductor) tube

The utility model belongs to the technical field of constant current source power supplies, and particularly relates to a constant current power supply circuit and a switching power supply circuit using a depletion mode MOS (Metal Oxide Semiconductor) tube. The constant-current power supply circuit comprises a depletion type MOS tube, the drain electrode of the depletion type MOS tube is connected with the positive electrode of a power supply, a resistor R2 is connected between the grid electrode and the source electrode, and the grid electrode serves as the output end of a constant-current source and generates starting voltage. According to the utility model, the constant current source composed of the depletion type MOS tubes is used for replacing a traditional RSTART starting circuit, perfect constant current is designed, it can be ensured that a chip has constant current when working in the whole voltage range, an auxiliary winding can be omitted, and normal working of a system is ensured. 本实用新型属于恒流源电源技术领