5V 1A SMPS Circuit

In this article we will teach how to make a small 5V 1A SMPS Circuit.

This circuit changes AC power to 5V 1 amp because of this maybe many people are looking for this.

It uses one small chip called TNY267P.

This chip work like ON/OFF switch and also control the current.

It act like tiny power supply inside which does not get too hot and it also make power for itself from main circuit.

All this fit in small box like 555 timer chip.

TNY267P chip work very fast around 132,000 times in one second and it can handle up to 700 volts.

What is a 5V 1A SMPS Circuit:

This 5V 1A (1000mA) SMPS is a power supply circuit.

It give max 1 amp current and keep output voltage always 5V stable and controlled.

This kind of power supply are mostly used for microcontrollers, small electronic things and low power devices.

Circuit Working:

Parts List:

This circuit use half wave rectifier because design is simple and power needed is very low.

Voltage spikes are blocked using one transil Zener diode rated at 180V.

Another way is to use resistor and capacitor in parallel instead of transil.

For feedback it uses opto coupler.

Output voltage is set by picking correct Zener diode ZD.

ZD voltage should be about 1V more than wanted output because opto coupler LED drop some voltage.

Example: If we want 5V output then use 5.6V ZD.

Not only 5V is possible, output voltage can change for that we need to do just two things:

Change secondary coil winding around 1.4 turns per volt.

Choose ZD with voltage about 1V more than wanted output.

If using this supply for low volt like 5V or less then better to use Schottky diode instead of fast diode it gives better efficiency.

This power supply when put in adapter and given 230V input can give about 13 watts max output.

Transformer Building:

This project uses small transformer with ferrite EE core.

Middle part of core which is center column is 4.5mm x 4.5mm and it have small air gap of 0.4mm.

Primary side have 140 turns of thin wire which is 0.15mm.

For 5V output secondary side have 27 turns of thicker wire of 0.4mm.

Because power is low no need to split secondary winding.

How to build transformer:

First wind all 140 turns of primary winding and be sure layers are neat and connected well.

Put copper tape between primary and secondary as shield and connect tape to cold end of primary.

Be careful with no short circuit!

Use strong insulation like 12 layers of duct tape or other strong tape.

Then wind the 27 turns of secondary wire.

To reduce noise or interference we can add small capacitor around 1nF/Y1 type between primary and secondary.

For more settings check datasheet of TNY263 or TNY268 series.

Remember:

Higher number in series means more power support.

Newer series like Tiny Switch-III (like TNY274 to TNY280) can give more power.

We can use these too and just check the pin connections some may be different.

Safety Caution:

Switching power supply work with high mains voltage which is not safe for beginners.

If circuit is not made properly then mains voltage can come to output side which can prove very dangerous.

Even after unplugging from mains the capacitors can still hold big voltage and give shock.

So build and use this circuit at ones own risk.

If anything bad happen to health or property author is not responsible.

Transformer Formulas:

Step 1 Find Primary Turns (Np):

Use this formula:

Np = Vin × 108 / (4.44 × f × B × Ac)

where:

• Vin is input voltage in volts
• f is working frequency in Hz
• B is magnetic flux for ferrite which uses around 0.3T
• Ac is core area in square meters

Step 2 Find Secondary Turns (Ns):

Ns = Np × Vout / Vin

where,

• Vout is output voltage in volts.

Step 3 Calculate Output Voltage (Vout):

Vout = VZD + VLED

where,

• VZD is Zener diode voltage
• VLED is voltage drop across opto LED which is usually around 1V

Step 4 Turns per Volt (TpV):

TpV = Ns / Vout

This gives how many turns needed for 1 volt on secondary side.

Choose Zener diode with voltage about 1V more than wanted output voltage to cover LED voltage drop.

Now use TpV to wind correct number of turns on transformer for the output voltage.

Build the circuit as per diagram.

For better efficiency at 5V or less replace fast diode with Schottky diode.

If noise problem happens add noise filter circuit.

Also for safety and isolation we can add a 1nF/Y1 capacitor between primary and secondary side.

Now the simple 5V 1A SMPS circuit is ready to work with 220V or 120V AC.

Note:

If anyone face problem while making this circuit feel free to ask in the comments.

Conclusion:

This 5V 1A SMPS circuit is designed with safety, temperature control and proper rules in mind.

If using for commercial or industrial use always follow correct design standards and safety rules.

References:

5V SMPS Design

5 V SMPS demo board