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7805 getting heat

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cakrawibawa

New Member
Dear all,

I'm creating a 7805 based circuit for charging my cellphone when driving my motorcycle.

This circuit powered from the accu. It work normal when the motorcycle is off. but when I'm driving, it getting heated.

Is it caused by the high current from the alternator/coil?
What should I modify to make it work normal when I'm driving my motorcycle?

any help is highly appreciated.
Thanks, Cakra
 

picbits

Well-Known Member
Do you have a heatsink on it ?
What is your measured voltage across the input pins when your motorcycle is running ?
What is the output current ?
Have you got filter capacitors on the input and output ?
What is the ambient temperature ?
If you are using a heatsink, what size is it ?
Is there any airflow around the heatsink ?
 

mvs sarma

Well-Known Member
Dear all,

I'm creating a 7805 based circuit for charging my cellphone when driving my motorcycle.

This circuit powered from the accu. It work normal when the motorcycle is off. but when I'm driving, it getting heated.

Is it caused by the high current from the alternator/coil?
What should I modify to make it work normal when I'm driving my motorcycle?

any help is highly appreciated.
Thanks, Cakra
while traveling if the headlight is OFF during day time , the voltage at the battery terminals would be almost 14V. Think that you are trying to draw 200mA approx. The difference is 7V and current is 0.2 A, hence 3.5watts is wasted across 7805 which causes the heat. Better follow the suggestion given by Picbits by providing a suitable heatsink.
 

ayushsk

New Member
while traveling if the headlight is OFF during day time , it means ic7805 drive on more current .One thing you can do - one low value resistance approximatly 10 ohm 1- 2 watt, added in series with input terminal of LM7805 ic as well as providing heat sink to the IC LM7805. and insure cooling of charger should be there.

regards,

s.k.singh
 

Hero999

Banned
Try the black regulator, 5V 200mA output, 88% efficient so no heatsink required and probably costs the same or less than the LM7805 plus capacitors and heatsink.
Official Home Page of Roman Black
 
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