Simple 5V 1A SMPS Circuit

A simple power supply that converts AC current to 5V at 1 amp is the project I wanted to build.

This circuit uses a little chip IC TNY267P.

This device functions as an on/off switch and current controller which is much like a miniature power supply system and
prevents itself from overheating and even generates electricity from the main circuit for its own needs.

All of this fits in a tiny box much like the commonly used 555 IC chip.

The TNY267P chip operates at a high speed of 132,000 times per second and faces voltages up to 700V.

What is a 5V 1A SMPS Circuit:

A simple 5V 1A 1000mA SMPS Switched Mode Power Supply circuit is designed to offer a maximum current output of 1 ampere together with a constant and controlled output voltage of 5V.

These types of power supply are often used to supply power to microcontrollers, small electronics and other low power applications.

Circuit Working:

Parts List:

A half wave rectifier was chosen because of this designs very low power requirements.

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

Another option is transit 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 example, if you aim for a 5V output you should opt for a ZD with an 5.6V rating.

Certainly, I do not limit you to stick to a 5V output, the output voltage is 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 go through the datasheet for the TNY263 – TNY268 series.

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

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

These can be integrated into the schematic provided above 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 Formulas:

First 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 around 0.3 T for ferrite cores.
• Ac is the core cross sectional area in square meters.

Second 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.

Third calculate the output voltage Vout using the selected Zener diode ZD and optocoupler voltage drop VLED:

V_out = V_ZD + V_LED

Fourth calculate the turns as per volt TpV for the secondary winding of the transformer:

T_pV = N_s / V_out

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

Calculate the turns as per volt TpV for the secondary winding of the transformer using formula 4.

Construct the circuit according to the provided schematic diagram.

A Schottky diode can be used in place of the fast diode to increase efficiency if the output voltage is 5V or less.

A noise suppression circuit could be an option if you experience interference problems.

If required add a 1nF/Y1 capacitor between the primary and secondary sides to enhance isolation.

The construction of a simple 5V 1 amp SMPS circuit for all 220V or 120V AC inputs is now complete.

Please use the comments section to ask any other questions you may have.

Conclusion:

A simple 5V 1A SMPS circuit is designed or controlled with safety measures, temperature control and compliance with applicable laws in mind.

Especially for power supplies used for commercial or industrial purposes its essential to adhere established standards of design and safety rules.

References

5V SMPS Design

5 V SMPS demo board