Wednesday, December 3, 2014

5V Multi-purpose SMPS

Good afternoon everyone, been a long time since I wrote something so here I am with very handy circuit diagram, a 5V 3.0A SMPS(Switched-Mode Power Supply) that requires only a few external components.

I have previously posted linear voltage regulators which are very simple in design and working but has a very big down side which is low efficiency. Switched-mode power supply can be complex but it's efficiency is much higher than linear regulator, even if the difference between input and output voltage is very high. If you recall my previous post you should know that the larger the difference is between Input and Output voltage for Linear regulator, more power it will waste. So, a simple switched-mode power supply can be very helpful mitigating that loss, production of heat and can be used in a versatile situation.

Scope of using:

This diagram can be used in many different scenarios, let me jot down a few of them.

1. If you want to run a Raspberry Pi/Banana Pi or similar products with a lot of external components like sensors and relay boards an efficient and high current supply will be very useful.

2. Want to make a portable charger that will charge your tablet or phone from battery? This will be perfect for its compact design, efficiency and cost effectiveness.

3. Your desktop computer is not putting enough current on the USB ports? You can make one of this and hook it up with the 12V rail of the computer power supply unit to get high current for charging* tablets fast or run any other external device.*****

And many more similar situations.

Components needed:

As mentioned above this diagram requires only a few external components it so the list will not be that long.

1. Integrated circuit - LM2576 5.0.
2. Capacitor - One 100uF 50V, One 1000uF 16V(Low ESR capacitor will be better) **.
3. Inductor - 100uH.
4. Diode - 1N5822 ( No, 1N4007 will not work) ***.

The LM2576 5.0

At the very heart of the diagram there is this integrated circuit LM2576 5.0. It provides all the active function for step down(Buck Conversion) switching regulation. This integrated circuit is enough for driving load up-to 3.0A and it has excellent line and load regulation.

As I was saying earlier, it requires only a few external components and it is very efficient, about 77% efficiency with an input voltage of 12V.

It also has protections like thermal shutdown and current limit protection. So in a very small package this integrated circuit is just perfect.

LM2576 Pin Out
Datasheet of LM2576.

The diagram :

Time for the diagram!

As you can see it requires only a few components it should be very easy to make. Moreover I will post about how switched-mode power supply works so not going to talk about it right now.

Final Result:

After assembling the circuit and testing the connections with continuity tester to make sure everything is in order I powered it up and all the measurements were fine. From an input of 19V it successfully put an output of 4.9V-5.0V. I had connected a DC Ammeter momentarily**** and the first reading that I had seen was about 5.5A, which is pretty high. the continuous current rating was about 3.0A which is sufficient for most works.


More Information and Caution:

       * While charging Lithium Ion bear in mind that charging this type of battery can be dangerous. High amount of charging current or voltage over the specification can lead to fire hazard. So limit the charging current to half of it's capacity. That means for a 2000mAh Lithium Ion use up-to 1000mA of charging current. Also you need to be careful while playing with the computer power supply unit, you might get shock. Learn more about computer power supply unit. Charging via USB is also a bit tricky though. Different device often negotiate with the charger to tell each other they are capable of fast charging, if this handshake doesn't occur devices won't pull much power from the USB port. To get about 1A you can simply short out the Data Lines of the USB also make sure not to connect that USB to any internal USB header of the motherboard.

     ** For the input section capacitor, the 100uF one, you can use a lower voltage one if your input voltage is low and for the output one it is better to use a low ESR capacitor, as it is a switched-mode power supply unit. Learn more about ESR.

    *** 1N5822 is a Schottky barrier diode, these type of diodes has low voltage drop and suitable for high speed operation. Learn more about Schottky diode and here is a datasheet of 1N5822. You can also use MBR350 if you want to.

 **** Don't use the ammeter directly with a power supply source, as it actually shorts out the output leads of the power supply and might be hazardous.

*****You can just bypass the motherboard to connect the USB directly with the computer power supply unit but that current will be really detrimental, If you short it out it will actually short the entire 5V rail of the power supply so it will not be that safe.


Anyway so that was all for now. Happy experimenting! If you want you can read my other posts here.


  1. How to set current limit for this LM 2576. If I want 1 amp what should i do.

    1. Your load will determine how much current it will need but if you want to limit the current to 1A max, simply use a LM 2575.

  2. Do I need always a Transformer ? That will give me a 12 VDC in the input ? for example to power a Raspberry PI from AC - DC. Thanks.

    1. You don't, you can power the circuit with a 6 cell Sealed lead acid if you want, that will power a Raspberry Pi just fine. But if you want to make a power supply that will be powered from AC main line, you will need a transformer and rectification circuitry as an input power for this circuit.

  3. To make a charger which needs 5v,1A will the above circuit be enough

    1. Yes, it will be able to deliver up to 3A, so 1A is not an issue.