Flash Power Supply Schematic Analysis and Design

The flash memory needs to add a 12V power supply voltage when writing data. The attached figure is a circuit for switching the output voltage of the power supply when writing data to the flash memory using a single-chip microcomputer. The control signal comes from the single-chip microcomputer. When the control signal is "L" (low level), the output end of the power supply circuit outputs a 11.8V power supply voltage to the flash memory. When the control signal is "H" (high level).

The output voltage of the power circuit is zero.

The transistors Tr1 and Tr2 both operate in a switching state.

Diodes D1 and D2 are rectifier diodes connected to prevent reverse current. When the control signal is high (+5V), the voltage of the (3) pin (ADJ) of the integrated circuit IC1 is greater than Vref (1.26v). At this time, Tr1 is controlled by the voltage of the (1) pin of IC1 and is in the cut-off state, so the output voltage is zero. Tr2 is controlled by the high-level control signal and is in the saturated conduction state. The connection line for writing the flash memory to the power supply is grounded to prevent the flash memory from malfunctioning due to noise voltage. When the control signal is low (0V), the voltage of the (3) pin of IC1 is less than 1.26V, and Tr1 becomes conductive.

Tr2 is turned off, so the output end of the power supply outputs a voltage of 11.8V. The maximum output current of the circuit is 200mA.