Simple 220V SMPS Circuit using One Transistor

This guide shows you how to build a simple power supply circuit that plugs into the wall outlet 220V and uses only one transistor MJE13005.

It does not need any fancy chips or extra parts to control the power.

Instead of those parts, it uses a special diode and a winding on the transformer to indirectly control the voltage output.

This keeps the voltage from getting too high.

What is a 220V SMPS Circuit:

A 220V SMPS Switched Mode Power Supply circuit is designed to convert a 220V AC alternating current input voltage into a stable DC direct current output voltage.

SMPS circuits are widely used in various electronic devices such as computers, LED drivers and other electronic equipment to provide a regulated and efficient power supply.

Circuit Working:

Parts List:

Transformer Winding Details:

Use a small EE ferrite core transformer with a central pillar having a cross section of 4.5 x 4.5 mm and an air gap of 0.4 mm.

This core can be sourced from the auxiliary transformer of an ATX power supply.

Wind 1st primary winding with 200 turns of a 0.12 mm diameter wire.

Wind the first half of the primary with 100 turns, followed by a thick layer of insulation.

Continue with the secondary winding 3rd, another thick layer of insulation, the auxiliary winding 2nd, a thinner layer of insulation and complete the second half of the primary 1st with 100 turns in the same direction.

Formula for transformer winding:

In a 220V SMPS circuit, the primary winding Np of a transformer is calculated as follows:

N_p = ( V_in(nom) x 10⁸ ) / ( 4 x f x B_max x A_e )

where:

• Vin(nom): Nominal input voltage (in your case, 220V RMS) – you will need to account for peak voltage as well
• f: Switching frequency (in Hz) – a common range for SMPS circuits is 50kHz to 200kHz
• Bmax: Maximum flux density in the transformer core (in gauss) – typical range is 1200 to 2000 Gauss (a trade-off between core size and efficiency)
• Ae: Effective cross sectional area of the transformer core (in cm²) – found in the datasheet of your chosen core

Transistor and Diode Placement:

Connect the transistor T1 to the primary winding and ensure proper insulation.

Place the zener diode to regulate the base current of T1.

For small voltages (6V or less), use a schottky diode, otherwise, use a fast diode for higher voltages.

Capacitor Installation:

Connect capacitors according to the circuit design, with emphasis on polarity.

C2 is crucial for voltage regulation deriving the output voltage indirectly.

Resistor Connection:

Integrate resistors into the circuit as specified ensuring the correct values are used.

Insulation Layers:

Apply insulation layers between windings to prevent short circuits and ensure safety.

Output Voltage Adjustment:

Adjust the output voltage by changing the number of turns in the secondary winding 3rd.

Consider the voltage drop across diode D1 when determining the desired output voltage.

Testing:

Use a multimeter to check for continuity and correct wiring.

Apply power cautiously, monitoring the output voltage and ensuring it matches the desired level.

Heat Sink Addition Optional:

If aiming for higher power output attach a heat sink to the transistor T1 to dissipate heat effectively.

Component Selection

Transistor Selection:

If you do not get MJE13005, then you can choose a transistor for T1 with Ucb = 800V and Uce = 450V or higher.

Options include KSC5027, 2SC3150, 2SC3457, 2SC2979, 2SC2866, or BUT11AF (economically available).

Output Voltage Adjustment:

Adjust the output voltage by changing the number of turns in the secondary winding 3rd, with approximately 1.17 turns/V.

Account for the voltage drop across diode D1 when determining the desired output voltage.

Diode Selection:

For small voltages approximately 6V or less replace diode D1 with a schottky diode rated at 40V or higher.

Caution and Warning:

Due to the involvement of fatal mains voltage, this switching supply is not recommended for beginners.

Poor design may lead to mains voltage reaching the output exercise extreme caution.

Capacitors may retain dangerous voltages even when disconnected from mains power.

All activities related to this project are undertaken at the individuals own risk and the author assumes no responsibility for any harm to health or property.

Conclusion:

By following the above methods, the enthusiasts can create a unique and efficient self oscillating.

One transistor 220V SMPS circuit with adjustable output voltage all while avoiding the complexities of integrated circuits and optocouplers.

References

MJE13005 Datasheet