I have designed a mobile phone charger according to following circuit diagram. Its input is AC220V and gives output DC5V, gives current upto 400mA. fortunately this is working and charging my simple NOKIA mobile phones. but when

(1) I attach a smart phone, the touch pad is disturbed i.e hang and not work properly. I dont know what is this problem with charger.however other chargers from market work fine.

(2) Also I want to increase current rating upto 1A, how can I do this.?

anybody help me out, I will be thankful...!

SMPS mobile phone charger circuit design

enter image description here

  • 1
    \$\begingroup\$ What does a smart phone need regards current when charging? \$\endgroup\$
    – Andy aka
    Commented Dec 24, 2015 at 14:57
  • 5
    \$\begingroup\$ You have a lot of courage ! Building a "charger" like that without understanding what a smartphone actually needs to charge it's battery. Without understanding what makes a good charger (hint: the good ones have a voltage feedback). Not even understanding how you can increase it's current rating, heck, you designed it, you must know. Or did you just slap some components together ? And why build this anyway when there are proper ones for sale everywhere. \$\endgroup\$ Commented Dec 24, 2015 at 15:40
  • \$\begingroup\$ @IgnacioVazquez-Abrams yeah I know it can be more than an amp but my question was more about steering the OP to realize why his circuit won't work. \$\endgroup\$
    – Andy aka
    Commented Dec 24, 2015 at 17:00
  • \$\begingroup\$ I m very sorry, I m new to apply my concepts practically. some of concepts may be wrong but want to try my best towards making a valuable product. for this purpose I post question for more knowledge and to learn/understand new concepts by others... \$\endgroup\$ Commented Dec 25, 2015 at 11:18

1 Answer 1


The circuit you show is actually a typical cheap charger design from the days of your old Nokia phone. It provides mediocre regulation and noise level, but should be quite resistant to overload conditions and output short circuit. In case of overload, output voltage will drop out of regulation, but likely no harm is done to the supply.

It works by transferring fixed energy pulses through the flyback transformer, increasing their delay if the output voltage gets high. Obviously, the energy of the pulses multiplied by the frequency you obtain at zero delay limits your output power. The transformer design determines both the energy per pulse (by its saturation level) and the maximal pulse frequency (by saturation level and inductance). To increase output power, you most likely should use a bigger core. Core material matters, this kind of converter depends heavily on the shape of the hysteresis curve. An easy approach to tripple the output current from 400mA to 1200mA would be using three of the cores instead of just one, and winding around the stack of three. This has the advantage of using a known-good core material for this application, and being able to scale to the "bigger" core without needing core data sheets.

As this circuits charges the core into saturation every cycle, using three cores means that you can charge three times as much energy into the combined core. Energy charged into the core is of course the energy "consumed" by it, which is roughly the input voltage (around 300V on 230V AC) multiplied by the average current multiplied by charging time. You can not change the input voltage, you should not change the charging time, so you need to triple the average current, which means to triple the peak current. To reach the triple peak current in the same time, the inductance of your transformer needs to be cut down to one third. On the other hand, three cores make the triple inductance of of just one core, so if you use three cores and make the same amount of turns, the inductance is too high by a factor of 9. Inductance scales with the square of the turn count, so you need to cut the turn count by a factor of three. This makes 26 turns for the primary, 4 turns for the secondary and 4 turns for the control winding. As you get currents up to three times as high, thicker wire might be needed, also the current sense resistor R4 needs to be reduced to 3.3 Ohms. I feel confident that the MJE13003 should be able to handle the increased load, but no guarantees on that.

To keep the ouput voltage from rising too high, this circuit includes R6 as dummy load. You should reduce it to 270 Ohms to keep the dummy load at the same fraction of the maximum load. Having R6 too high results in a overly high output voltage or even circuit instability on low load (worst case: no phone connected).

If you can't wind the core yourself, just paralleling three of the same kind of transformers without changing the turn counts should result in the same result as one big transformer with reduced turn counts.

The touchscreen malfunction is caused by the excessive amount of high-frequency noise produced by this supply. Using a C-L-C output filter will likely fix it. Make sure to use low-ESR capacitors. The series resistance (at 100kHz) of the capacitors needs to be specified in the datasheet (if it is not, it's not an low-ESR cap), and should be below 50 milli-Ohms. Capacitor values don't matter as much as the series resistance.


simulate this circuit – Schematic created using CircuitLab

If you have a grounded plug, connect the ground pin to the negative output (either directly or using 100nF || 470kOhm if you desire quasi-floating output). Additionally, try adding a common-mode choke if the C-L-C filter does not help. If even with a C-L-C filter containing low-ESR caps and a common mode choke you still can't get the touch screen to work, chances are that your supply does not operate stable at all. In this case, all bets are off for remote debugging.

  • \$\begingroup\$ thank you for your answer.! I could not understand how to increase current rating.? should I wind more thick wire on chopper core? which one primer or secondary? Also I tried much to resolve touch disturbance problem using capacitor and inductor filters etc, but failed. Any suggestion how to implement filters? is there any other revised circuit diagram for SMPS mobile phone charger which I could easily implement and test please share with me. thanx \$\endgroup\$ Commented Dec 25, 2015 at 11:23
  • \$\begingroup\$ The power of this converter is not limited by the resistance of the wires, but by the energy capacity of the core. For increased power, calculate your design with a core of approximately three times the saturation energy as the core you currently use. Then calculate turn counts so that you obtain around the same time to charge/discharge the core. Do not change the winding ratio. Decrease the dummy load resistor by a factor of three, as tripple maximum output current also means tripple minimum output current. Please add to your question what you tried to combat noise output. \$\endgroup\$ Commented Dec 25, 2015 at 11:55
  • \$\begingroup\$ ok I try this. I tried different capacitor values for filtering output. also applied 2.2uH inductor at output to filter but not succeeded. I want to know that if I use any other chopper having same turns ratio but bigger core size, should it work correct in my circuit? \$\endgroup\$ Commented Dec 25, 2015 at 12:38
  • \$\begingroup\$ Please see my edit about increasing the output current. Please note that this does not imply the suggested modification is as safe or conformant to EMI regulations as the original! Please add a schematic to your question on how you tried to add the inductor and/or capacitors, and compare that to diagrams of a C-L-C-filter. Please specify what model of caps you used. \$\endgroup\$ Commented Dec 25, 2015 at 15:32
  • \$\begingroup\$ I have gone through your edited answer and able to understand some basic concepts. so, now I will implement the same to increase current rating and will share results soon with you ... also I have edited schematic which I had applied filters to remove noise to set touchscreen mulfunctioning. please see it .... please let me know if there any other valid solution for this problem! \$\endgroup\$ Commented Dec 27, 2015 at 18:19

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