The following content explains a simple 12V, 1 Amp switch mode power supply (SMPS) circuit using the very reliable VIPerXX IC from ST microelectronics.


With the advent of modern ICs and circuits, the age old iron transformer type of power supply are surely becoming obsolete. Today power supplies are much compact, smaller and efficient with their functioning. Here we discuss one outstanding switch mode power supply circuit which can be easily built at home for deriving clean, ripple free 12 V DC.

Thanks to ST Microelectronics IC, the VIPer22A, which has made the construction of truly efficient and compact SMPS power supply unit possible that too by using a very few number of electronic parts.As can be seen in the picture, the circuit is indeed very small, compared to the power that is available from it. It's just 50 by 40 mm in its dimensions.The circuit diagram is very easy to understand, let's study it with the following points:

How the SMPS Circuit is Designed to Work

Looking at the figure we can easily see that the configuration does not involve too many stages or parts.

The input mains AC, as usual is first rectified using ordinary 1N4007 diodes which is fixed in the bridge network mode.

The rectified high voltage DC is filtered using the high voltage capacitor.

The next stage is the crucial one which incorporates the outstanding chip VIPer 22A manufactured by ST Microelectronics.

The IC alone functions as the oscillator and induces a frequency of around 100 KHz into the primary winding of the ferrite E core transformer.

The IC is absolutely rugged and is internally protected from sudden voltage in rush and other voltage related component hazards.

The IC also incorporates built in over heat protection which makes the IC virtually indestructible.

The voltage induced at the input is effectively stepped down at the output winding, due to low eddy current losses, about 1 amp current becomes available from a relatively tiny ferrite transformer.

With the coil specs shown the voltage is around 12 and the current is around 1amp.

A special feedback circuitry is also included in the circuit for maintaining high degree of protection and power saving features.

The feedback loop is implemented via an opto-coupler which becomes active during abnormal circuit conditions.

When the output voltage tends to rise beyond the set threshold the feed back loop becomes operative and feeds an error signal to the IC FB input.

The IC instantly comes into an corrective mode and switches off the input to the primary winding until the output returns to the normal range.

Circuit Diagram

simple 12V 1 amp SMPS circuit

PCB Layout

simple 12V 1 amp smps PCB layout

Transformer Winding Data

simple 12V 1 amp smps ferrite transformer winding data

Another 12V 1 amp simple SMPS using IC  TNY267

 12V 1amp smps circuit using TNY

How it Works

The simple smps circuit shown above uses the popular tiny switch IC TNY267. It is a tiny mosfet based 120V to 220V switching oscillator IC which only requires configuring with a ferrite transformer and a stepped down Vdd operating voltage.

The design is so simple that a mere visualization of the schematic is enough to tell us the functioning details quickly.

The stepped down start voltage is acquired from stabilizing network using a 180V zener diodes and the fast recovery diode BA159 after rectifying the mains 220V through a 1N4007 diodes and the 10uF/400V filter capacitor.

As soon as this voltage is applied to the IC, it begins oscillating and its internal mosfet begins switching the ferrite transformer primary at the predetermined oscillating frequency.

Being a flyback design, the secondary also starts conducting during the OFF cycles of the primary through mutual induction and generates the required 12V voltage at the output side.

This voltage may not be stabilized, therefore an opto-coupler based feedback is used and the link is configured with the exclusive shut down pinout 4 of the IC.

This ensures that the output never exceeds, and remains fixed at 12V 1 amp proportion.

Transformer Winding Data

The transformer winding is actually quite straightforward, and may be done in the following manner. Keep in mind that the black dots indicate the start points of the winding which is very important, and must be strictly followed while winding the transformer.

The primary wound using 36 SWK super enameled copper wire upto 150 turns, while the secondary is wound using 26 SWG wire upto around 12 to 15 turns.

The core can be a standard E19 type ferrite core having a bobbin with central core cross section area of approximately 4.5mm by 4.5mm.

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