Here we learn about a simple switch mode power supply (SMPS) circuit which is capable of delivering 3.3V, 5V, 9V at around 800mA from a Mains input range of 100V to 285V, with a complete isolation.

The functioning of the proposed 3.3V, 5V, 9V flyback SMPS Circuit may be understood by going through the following detailed circuit explanation:

Input EMI Filtering

The capacitor C10, together with C13 form the main capacitors. In conjunction with L4, they constitute the EMI filter stage.

Tiny Switch's integrated frequency jitter facilitates to accomplish a reduced EMI even with a rather uncomplicated EMI filter configuration.

Primary Clamp Snubber Stage

D3, R1, R2, along with C1 build up the primary side clamp-snubber to fix the voltage peak at the Drain pin as soon as its turned-off. D3 is a 1N4007G, a glass-passivated model of the typical 1N4007, with regulated back EMF restoration. Its positioned, in conjunction with R2, to enhance EMI and the intended 3.3V, 5V, 9V outputs.

In a situation where a specific fast recovery diode is difficult to obtain, any other alternative fast diode can be incorporated without an issue.

Output voltage filtering

C3, C5, and C7 become responsible as the bulk output capacitors. C4, C6, and C8, in conjunction with the inductors L1, L2, and L3, constitute second-stage output filters.

Output Feedback Loop

Sensing resistors R4 and R5 detect and identify a probable difference in the amplitude of the 3.3V and 5V
output voltage limits.

Such difference in the voltage, could be as a result of differences in the output connected load or perhaps input voltage, are fed as a reference to the input pin of the TL431 shunt regulator.

The shunt regulator identifies these and compares the same with its in-built voltage reference level to trigger a feedback signal in the form of a current impulse trough U1 B proportional to the to the identified difference detected by R4 and R5.

Opto-coupler U1 immediately shuts down the control loop of the supply voltage by sending the feedback signal current to the output of the ENUV pin on the primary section of the circuit.

The following diagram represents the complete schematic of the 3.3V, 5V, 9V SMPS Circuit

Circuit Diagram

3.3V, 5V, 9V SMPS Circuit

PCB Layout for the proposed multiple voltage output SMPS circuit

PCB layout for 3.3V, 5V, 9V SMPS Circuit

Transformer winding drawing for the above explained multiple voltage output SMPS circuit

Transformer Winding Details

The following gives the transformer specifications for assisting the winding of the turns correctly


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