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Single Transistor Mobile Phone Charger

The Single transistor mobile phone charger is known for its size, price, and easy usage.

These cheap mobile charger use only a few parts, a very simple SMPS design.

But there's a drawback too, they got damaged easily.

The input voltage is 110-220V 50Hz, and the output power is 7.4-9V 800mA in no-load.

It can be used for charging Mobile/Smart phone batteries, electronics projects, driving LEDs or small loads, etc.

Single transistor Mobile phone charger Specification

The quick specification of Single Transistor Mobile phone charger:

  • Type: Charger, SMPS
  • Input Voltage: 110V to 220V
  • Frequency: 50Hz
  • Output Voltage: 7.4V to 9V
  • Output Current: 800 mA
  • Connector Type: Jack
  • Protection: NA
  • Auto Cut OFF: NA

Single transistor Mobile phone charger Circuit diagram

Schematic of Single transistor mobile phone charger circuit shown below.

Transformer details of this Charger

  • Model: EE16
  • Phase: single
  • Usage: SMPS
  • Core Type: Small EE-type ferrite core transformer (no air gaps).
  • Primary Winding (L1): 250 turns with 36 to 40 SWG insulated copper wire.
  • Secondary Winding (L2): 6 turns of 26 to 28 SWG insulated copper wire.
  • Feedback Winding (L3): 12 turns with 36 to 40 SWG insulated copper wire.

Working principle of Single transistor Mobile phone charger circuit

When the single transistor mobile phone charger circuit is connected in the 220V AC mains supply, the half-wave rectification is started.

This rectification circuit made with 1n4007 diode, 2.2uF 400V capacitor, and 1Ω 1W resistor.

It rectifies and filters the AC input to high voltage DC.

This means the rectifier voltage passes the next stage (self-oscillating flyback oscillator) with high voltage DC.

The voltage between node A and node B is approximate:

  • 150 volts for 110V AC input
  • 311 volts for 220V AC input

Next, the base of MJE13001 NPN transistor (Q1) starts opening as it's biased by the 1MΩ resistor.

The current through primary winding (L1) starts rising rapidly and reaches the threshold level within no time.

But at the same time, an opposite (but low) voltage starts rising across the auxiliary feedback winding (L3) of the transformer.

This opposite voltage starts charging the 2.2nF capacitor negatively, much faster than charging it through 1MΩ resistor.

Thus ultimately blocks current flow through primary winding (L1).

As there's no more current flow in the auxiliary feedback winding (L3).

So, the 2.2nF capacitor starts discharging through 360Ω resistor, L3.

The current through 1MΩ Resistor again starts opening the base of the transistor Q1.

This process repeats itself again and again very fast around 10,000 to 50,000 times a second, depending on various parameters.

When the transistor Q1 becomes off condition, the energy stored in the primary winding is dumped in the secondary winding as well.

This last stage is responsible for rectifying and filtering the induced current-voltage on the secondary winding (L2).

The rectified output voltage could be as high as 7.4-9 volts under no-load.

But, very quickly drops, when you connect with your mobile phone to charge.

A 2mm Red LED used as a power ON indicator and 1KΩ 0.25W resistor protects the LED.

Applications of Single transistor Mobile phone charger

  • It can be used as a Mobile phone charger
  • Smartphone charger
  • Used as a LED driver
  • Operating Small LOAD
  • Used as a Power Supply
  • Used in various Electronics projects

This portable mobile charger can be used as a power supply in the Safe Simple Lithium Cell Charger.

The single transistor mobile phone charger circuit is not for beginners. There is a chance for a fatal shock if anyone touched the circuit board.

Post a Comment


  1. Thank you Sir

    1. Sir ..Jou are amazing best explanation I found ..Have u any youtube channel

  2. When your website or blog goes live for the first time, it is exciting. That is until you realize no one but you and your.
    high voltage rectifier diodes

  3. Sir thanks for your diagram, i just want to know the name of transformer i can't find the transformer online bcz i don't know the name of transformer so kindly tell me the name?

    1. Hi Rana,

      The transformer model is 'EE16'.

      You will not find this single phase SMPS transformer exactly the same online.

      Therefore, you can make this transformer.

      I have given the information about the transformer windings in this article.

    2. Thanks Sir, can have possible to provide Transformer winding inductance and about required gap like Air gap or Zero gap or etc.

  4. A small correction. You have not explained the function of the 1N5237 zener diode. This is very important, and its purpose is to limit the output voltage.

  5. could somebody tell which is D2, C2 and C3? The last was a great explanation.

  6. Single transistor mobile phone charger is a portable smps design with single transistor 13001.


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