Author Options:

Excessive heat from my l7805cv voltage regulator? Answered

Hi, I'm a newbie and I've set up a programme using an Arduino Nano to build a high speed photography project using Bluetooth  (from a guy called ZHUT on youtube).
 I've used his schematic and  his App and it's almost there, but the l8705cv regulator is heating up fast (almost too hot to touch) after a few minutes( with a heatsink). I'm using a 9 volt dc adaptor, power coming out is 5 volts. The trigger threshold numbers (1023) don't come up on the app. to start the programme running, stays at zero.  I've never used a schematic before, so I think I've wired up something wrong to cause this. 
Any suggestions would be really welcome, as I've spent a long time on this and I'd love to get it going.
I'll send photos, hope they will help, thanks 



Best Answer 6 months ago

Hello, first of all make sure you have not made cabling errors, if everything is ok I can give you two simple suggestions to improve your project,

1) remove the double sided adhesive from the heatsink and secure it to the regulator by means of a small spring, or by means of a small bolt, the direct contact between the two metals will make the heat better dissipate.

2) replace the 9v battery with 4 1.5 AA batteries, this lowering of voltage will greatly reduce the dissipation on the controller, moreover you will have a greater autonomy.

I hope it helped youHi, I can give you two simple step to improve your project

1) take away the bihadesive from the heatsik and assicure it to 7805 with a little spring

Ciao,prima di tutto assicurati di non aver commesso errori di cablatura, se tutto è apposto posso darti due semplici suggerimenti per migliorare il tuo progetto,

1) togli il biadesivo dal dissipatore e assicuralo al regolatore tramite una piccola molla, o tramite un piccolo bullone, il contatto diretto tra i due metalli farà didssipare meglio il calore.

2) sostituisci la batteria da 9v con 4 batterie da 1,5 AA, questo abbassamento di tensione ridurrà di molto la dissipazione sul regolatore, inoltre avrai una maggiore autonomia.

Spero ti sia stato d'aiuto

Hi Apatrik, bolted my heatsink to the regulator after cleaning the surfaces, plugged in my 9 volt adapter and after 10 minutes it was just warm even with the LED lamp burning----Heat problem solved! going to adapt a battery holder to hold 4 x 1.5 batteries as you've suggested .

Many thanks for your help with that problem, can you tell me if my photos came through, I had a problem sending them ?

if you switch to 4 1.5V batteries the regulator is redundant. The Arduino has its own regulator. The only issue could be th he-06, is rated for 6v but to be on the safe side you can power it from the 5v pin on the Arduino. The rest of the circuit doesn’t require a precise voltage and will be fine at 6v.

YMMV, I’ve released a lot of magic smoke in my time.

It has been my experience that 78xxx seris regulators require considerable heat sinking to operate anywhere near their max threshold.

In addition, the ideal source voltage for a linear regulator of this type should be only a few volts greater than the output voltage to minimize resistive heating in the IC due to its natural dissipation (ie, say you're operating a 5VDC 7805 reg, from a 12VDC source, with a load current of 0.5A...that means you are dumping about

(12-5) x 0.5 = 7 x 0.5 = 3.5W in heat.


Use a lower source voltage per above

Reduce your load current.

If you don't actually "need" a linear regulator, use a switching regulator instead. They're more efficient.


6 months ago

Sorry, I thought photos had sent, I'll try again.


Links, schematics, something, please.

LM7805 has short circuit protection so my guess is it is loaded to the max.

How much current is your project drawing ?

Post your schematic, so we can see what its supposed to do - I'm not wasting my time digging for it.

Its either pulling too much current, or your heatsink is inadequate