Change 9 Volts to 5 Volts

About: Electronics have always been fascinating to me. Things that get my attention are clocks, lamps, motion activated devices, light activated devices, laser intruder alert systems,solar and wind power, voltage i...

Greetings to all my Instructable buddies. Today I'll show you how to convert 9 volts into 5 volts using the LM7805 fixed linear voltage regulator integrated circuit. If you would like more information about the LM7805 than I will be covering in this short Ible you should visit the Wikipedia page on this particular component.

Wikipedia's LM7805 page (actually titled 78XX)

Step 1: BOM (bill of Materials)

For this Instructable you will need:

  • 1 - LM7805 voltage regulator
  • 1 - Capacitor with the value of 0.33uF
  • 1 - Capacitor with the value of 0.1uF
  • 1 - 9 volt battery
  • 1 - 2.2 volt Red LED (you can use a different colored LED if you'd like, but then your final results may differ from what is displayed in the photos, ha!)
  • 1 - 150 ohm resistor

Step 2: Assemble and Use

I don't think any further explanation is needed at this point. But just in case. The positive lead from your battery goes to the left pin (input) on the LM7805. Attach one lead of the 0.33uF to the input pin and the other lead to ground. The output pin (right pin on the LM7805) will be your 5 volt source. Place the 0.1uF capacitor between the output pin and ground. In the example I'm using an LED as my 5 volt load. You could use whatever 5 volt device you need to use. There is a thing called "Dropout Value" which means your LM7805 will become unstable at about 2.5 volts above 5 volts on your input pin. In other words if you apply 7.5 volts or less to your input pin you may not get 5 volts from the output. One more thing I'd like to mention. You can apply more than 9 volts to the input pin. But (from the Wiki) the total power (voltage multiplied by current) going into the 7805 will be more than the output power provided. The difference is dissipated as heat. This means both that for some applications an adequate heatsink must be provided, and also that a (often substantial) portion of the input power is wasted during the process, rendering them less efficient than some other types of power supplies.

I hope this helps everyone who needed this information. Questions are welcomed.



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    10 Discussions


    1 year ago

    Hi, thanks, I needed just that, a small 5 volt power supply to run a little arduino count down timer off a 9 volt battery. Wife needed one for her eye drops to take care of her glucoma, she needs to time the drops for 2.5 minutes after insertion, she has been squinting at a watch watching the second hand with one eye whilst covering the other. I had the unit built up but the blasted little Arduino that I was using failed on the raw in voltage. So I took a bit o strip board and soldered up one of these little guys and added it to the case, and vola! I have the device for my good wife of over 48 years. Added a small toggle switch to control it all, as well as a push button to shunt the reset pin to ground, soldered her all together then stuffed her in a plastic box, so she can reset the machine to count down should she miss with the drops.

    2 replies

    You can give it a try and see the results. I would think it would probably work but noise and ripple might make it unusable or too unstable. Please let me know what happens.


    3 years ago

    This is a great explanation as I am using ATtiny85 to power ultra micro servos because both need no more than 5 volts but had questions about the capacitors. I am wondering if you can substitue the 0.22 uF for the 0.0.33uF? Is it also possible to substitute 0.01uF for the 0.1uF? I too am trying to miniaturize projects. I like that you used the LM7805 and will try it with # papercircuits on my Paper Panda Robot Prototype #paperpandarobot


    3 years ago on Introduction

    I like the framed wall picture of the 7805! Looks like something I'd hang on my living wall! lol

    1 reply

    Yeah it's a great picture. I don't have a wife/girlfriend so 'decorating' is all up to me. In the living room are two nicely framed 8X10 pictures. One is of Albert E. and the other is a pic of Buzz Aldrin taken by N. Armstrong on the moon.

    UPDATE July 29, 2018. My living room wall now has 10 8X10 framed pictures. Sir Issac Newton, N. tesla, Mike Faraday, Carl sagan Dr Tyson, Lady Ada w/autograph, Isaac Asimov, Al Einstein, Buzz Aldrin, and Robert Downey Jr as Iron Man.