Simple 5V 1A SMPS Circuit

I tried to build a simple power supply that changes AC current to 5V at 1 amp.

I used a tiny chip called the TNY267P.

This chip is like a whole mini system for a power supply, it controls the current, turns it on and off, protects itself from overheating and even gets its own power from the main circuit.

It is all in a small package just like a popular chip called the 555 IC.

This TNY267P chip can handle up to 700V and works very fast i.e 132,000 times per second.

What is a 5V 1A SMPS Circuit:

A simple 5V 1A 1000mA SMPS Switched Mode Power Supply circuit is designed to provide a stable and regulated output voltage of 5V with a maximum current output of 1 ampere.

This type of power supply is commonly used to power small electronic devices, microcontrollers and other low power applications.

Circuit Diagram

Parts List:

Given the relatively low power requirements of this design a half wave rectifier was chosen.

Voltage peaks are capped using a transil zener diode with a 180V rating.

Alternatively, this transit can be substituted with a conventional parallel combination of a resistor and capacitor.

Feedback in this design is facilitated by opto couplers, and the desired output voltage is determined simply by selecting the appropriate zener diode.

The ZD voltage rating should be approximately 1V higher than the desired output voltage accounting for the voltage drop across the opto couplers LED.

For instance, if you aim for a 5V output, you should opt for a ZD with an 5.6V rating.

Of course, I do not constrain you to stick to a 5V output, the output voltage can be adjusted by modifying two key parameters:

Adjust the secondary winding turns per volt approx. 1.4 turns per volt.

Use a ZD with a rating approximately 1V lower than the desired output voltage.

If you plan to use this supply for lower voltages around 5V or lower replace the fast diode on the output with a schottky diode for better efficiency.

The maximum power output of this supply when enclosed in an adaptor and supplied with 230V, is approximately 13W.

Transformer Construction

The transformer used is a small ferrite EE core.

The central column of the core has a cross sectional area of 4.5 x 4.5 mm, with a 0.4 mm air gap.

The primary winding consists of 140 turns of 0.15 mm diameter wire while the secondary winding for a 5V output consist of 27 turns of 0.4 mm diameter wire.

Due to the low power nature of this supply, the secondary winding is not divided into two parts.

Here is a construction process for the transformer:

Wind the entire primary winding making sure to interlace the layers of the primary winding.

Use copper tape for shielding between the primary and secondary connecting it to the cold end of the primary ensure no short circuits are created.

Apply strong insulation such as 12 layers of duct tape.

Wind the secondary winding.

To mitigate interference issues consider adding a noise suppression circuit and/or placing a capacitor of approximately 1nF/Y1 between the primary and secondary sides.

For more detailed parameters and specifications, consult the datasheet for the TNY263 – TNY268 series.

Note that as the series number increases, the potential power handling capability also increases.

Additionally, be aware of the newer series, tiny switch-III, which includes ICs like TNY274 – TNY280, capable of handling even higher power levels.

These can be integrated into the schematic provided although the pinout may vary.

Safety Caution:

Switching power supplies involve mains voltage connections and are not suitable for beginners.

A poorly designed circuit can potentially expose mains voltage at the output.

Capacitors may retain dangerous voltages even after disconnection from the mains.

All construction and use are at your own risk, and I do not assume responsibility for any harm to health or property.

Transformer Calculations

Formula 1: Calculate the primary turns Np for the transformer:

N_p = V_in × 10⁸ / 4.44 × f × B × A_c

where:

• Vin is the input voltage (in volts).
• f is the operating frequency (in Hz).
• B is the magnetic flux density (typically 0.3 T for ferrite cores).
• Ac is the core cross sectional area (in square meters).

Formula 2: Calculate the secondary turns Ns for the transformer:

N_s = N_p × V_out / V_in

where:

• Vout is the desired output voltage (in volts).

Power Supply Schematic and Components

Formula 3: Calculate the output voltage Vout using the selected Zener diode ZD and optocoupler voltage drop VLED:

V_out = V_ZD + V_LED

Formula 4: Calculate the turns per volt TpV for the secondary winding:

T_pV = N_s / V_out

Select a Zener diode ZD with a voltage rating VZD approximately 1V higher than the desired output voltage Vout to account for the voltage drop across the opto couplers LED (VLED).

Calculate the turns per volt TpV for the secondary winding using Formula 4.

Construct the circuit according to the provided schematic diagram.

If the output voltage is lower around 5V or less, replace the fast diode with a Schottky diode for improved efficiency.

If you encounter interference issues, consider adding a noise suppression circuit.

Optionally, place a capacitor of approximately 1nF/Y1 between the primary and secondary sides for improved isolation.

This concludes our article on how to build a simple 5V 1 amp SMPS circuit for all 220V or 120V AC inputs, if you have any further questions please feel free to ask them through comments.

Conclusion:

When designing or working with a simple 5V 1A SMPS circuit, it is essential to consider safety precautions, thermal management, and adherence to relevant regulations.

Following established design guidelines and safety standards is crucial, especially for power supplies intended for commercial or industrial applications.

References

5V SMPS Design

5 V SMPS demo board