Power Supply Design for Micro controller projects(Your first Power Supply)

You may not believe if I say we have so much of electronics to learn and apply in simple 5V power supply design, which is first step in any micro controller  project(5V/3V digital worlds)

Now a days micro controllers are operational at 1.5V . Look at these examples of popular  micro controllers.

AVR family micro controller ATmega16 has operable voltage range of 2.7V-5.5V ATmega16L and 4.5V-5.5V ATmega16 respectively.

So,now  you  must know the importance of  5V power supply in micro controller world.

All DTL,TTL and CMOS circuits mostly operational well at 5V.

Now , to design your 5V power supply just follow these steps and it could be a simple exercise for beginner.

  • Block diagram:These are the design objectives to be met

Available 230V/50Hz  AC line has to stepped down to level acceptable  by  Rectifier (AC-DC converter ) and 5V regultor (regulates voltage at 5V irrespective of power line fluctuations and rectifier output variations).Along with these we need a filter which filters out high frequency components.

So resultant block diagram of simple Power supply is:

Power Supply General Block diagram

Voltage specification of supply is 5V.. then what do you think current specification of the power supply we need??

1A/1.5A must be sufficient for most of designs including RF tranciever inclded in project(RF  devices need more current compared to other moicro controller I/O as per my experience so far..!!)

Blocks to circuit:

First part is Transformer which  can step down AC 230V to 12V(Why not 5V??? you will answered just read further )

Rectifier: there are two options for this part one is you can buy an Integrated Circuit already designed by intelligent EngineersJ or you can yourself build a simple bridge rectifier.

If you are going for IC this is Part no.DI104 Rectifier IC.

Bridge rectifier uses four silicon rectifier diodes In4001 ,1A  arranged as shown:TR1 is transformer.

Bridge Rectifier using silicon rectifier diodes

Now we need a simple capacitive filter which can smooth out Half-sine wave from rectifier. Capacitor is energy storage passive electronic component which can store charge and discharge it when voltage across it falls below it’s charged voltage.This electronic nature of capacitor accomplishes the job of smoothing out Half- sine rectified wave.

Now smoothed DC should be regulated to remain within acceptable range around 5V.

Regulator: Regulators are available as Integrated Circuits (ICs).78XX family regulators are normally used.So, you can go for 7805 5V,1A regulators . Just go through data sheet and application note of 7805 from manufacturer Texas Instruments ua78XX datasheet & Application note.

There you can observe operable range(test conditions) is 7V-25V. Hope you got the answer to question above.:)

And output voltage range it can regulate is in the range 4.8V-5.25V.(don’t scratch your head if you don’t get exact 5V output from your supply)

Now go to Application Information in the document:  It’s mentioned why we need  reverse bias protection regulator(Fig.7 of document). So connect a diode parallel to regulator7805 and also two more capacitors as mentioned in document for proper design.

And now power supply is ready but use a simple network consisting of LED and resistor.This is for User indication that the supply is ON/OFF.

Note: As I mentioned in my previous post here.

1mA of current must be sufficient to glow indicator LED to observable brightness. We need more current to drive load which will be connected across this network so use very high resistor in series with indicator LED.ON resistance of LED is negligible. So use

5V/1mA= 5k ohm resistance.

Now Power supply is ready for your micro controller  project. This is complete circuit diagram :

Power Supply circuit


Same way you can design 8V and 12V power supplies needed to drive DC or Servo motors if used in project just by replacing 7805 by 7808 and 7812 respectively.

Don’t forget to make common ground for micro controller and I/O device circuits.Otherwise the project won’t work..!!!!

All specifications and  information are taken from respective data sheets(Components) and User manuals(Micro controllers).

Now make it..!!! Good luck..:)