regulator ic 7808 overheating issue

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Murugesh_89

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Hi,
I am using a 7808 smd type make of ST. The circuit draws 450 mA from the 7808. I gave 24V as input to the regulator ic.



I have also provided the heating dissipating area around its ground pad. But the IC is overheating and i cant able to place my finger over it for more than a half second.

As a result the output voltage reduces to 4 or 5 V after some 2 minutes from power ON. Then if i switch OFF and then ON the power supply it will be ok for next 2 minutes.

How do i get out of this issue?

Thanks,
Murugesh
 

24Vin, Vo = 8V, volt drop = 16 V, Power = 16 X .45 ~ 7W, in free air its rated at 50 degs/W, so temperature ~ 350 degs. No wonder its closing down!! Resistance case to junct = 3 degs/W. So a 21 degs temperature drop to case at your power. To keep junction below 120 degs, you need to dump about 60 degrees (allowing 40 degs for ambient) at 7 W, so you need a 9 degs/W heat sink. Some thing like this :- https://uk.farnell.com/aavid-thermalloy/sw50-2/heat-sink-to-220-218-8-6-c-w/dp/1213439
Frank
 
I dont use anymore 78xx linear regulators today unless I have very low amps consumption < 20mA or so
or really adapted to the input voltage no more than 2V, or you're sure it will heat a lot.
else I use a smps regulator, they are widely available and cheap and dont overheat
search for LM2576 and family.
 

Agree with Kripton.

Unless the power dissipation is below 1 watt, or the project is extremely cost sensitive, don't use a linear use a switcher.

Having said that, if you really require a linear regulator, then use the divide-and conquer scenario. Put a pre-regulator ahead of your regulator, set at 16 volts. That way, you split the heat among two devices.
 

I dont use anymore 78xx linear regulators today unless I have very low amps consumption < 20mA or so
Click to expand...
Hi
I use them but if i have low input voltage in compare with out put so the loss power will be low . ( sometimes it can be cheaper than LM2576 or any other kind of SMPS ) ( and more compact in simple designs )

Put a pre-regulator ahead of your regulator, set at 16 volts. That way, you split the heat among two devices.
Click to expand...
Or perhaps using a larger heat sink . or perhaps reducing the input voltage .


As a result :
1- reduce the input voltage
2- change it via a switch mode one .
3- Use a larger heat sink surface .


Good Luck
Goldsmith
 

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