EPIC Programmer running hot.

[fowardbias]

Is it normal for the LM317 and the 7805 voltage regulators to run intermittently hot. When I say hot I mean hot enough to be barely touchable. No smoke or smell of burning. Doesn't matter if there is a PIC plugged in the programming socket or if in program or idle mode. The unit still programs any of the PICs I am using. I added an aluminum heat sink to both regulators for ease of mind. Anyone encountered this? JS

[Luciano]

With a power supply of 16V DC, what is the current draw in mA?
(With and without the PIC).

I don't have this programmer but maybe somebody else can help you.

Luciano

[nimonia]

did u make or did u buy the epic... it should not be hot if u bought it..

[Darrel Taylor]

My epic gets pretty hot too. I layed a cigarette pack on it once and it melted the plastic on the outside. Stunk for a little while but that was it. I've had it a few years now and it's always been like that, and it always works. It's always powered up, so I assume it's not a problem.

Darrel

[fowardbias]

The Epic current draw is 140mA. with the red programming LED on. When the Led is off the current is 40mA. So far it's working OK. The heat sinks are working well. The plastic cases of both TO-220's are much cooler to the touch. Thanks all. JS

[Luciano]

Hi!

With a power dissipation of 0.35 Watt your LM317/TO220 doesn't need a heat sink.

How to calculate:

PD MAX = TjMAX − TaMAX
         _____________
             Rja

PD MAX = Maximum Power Dissipation (Watt)

TjMAX= maximum junction temperature (°C) 
For the LM317/TO220 is 125 °C.

TaMAX= maximum ambient air temperature (°C) 
Room temperature or temperature inside enclosure, example 30°C.

Rja= thermal resistance from junction to ambient without heat sink (°C/W) 
For the LM317/TO220 is 50 °C/W.

125 − 30
__________   = 1.9 Watt 
   50

1.9 watt is the maximum power dissipation of the LM317/TO220 without a heat sink.
(If you use the LM317 at TjMAX its life will be reduced).

In your case the input voltage of the LM317 is 16V and the output voltage is 13.5V.
The voltage difference is 2.5V. (16V - 13.5V).

The current is 140 mA. (0.14A)

The power dissipation of your LM317 is:
2.5V * 0.14 = 0.35 Watt

With a power dissipation of 0.35 Watt your LM317/TO220 doesn't need a heat sink.

Best regards,

Luciano