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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
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
did u make or did u buy the epic... it should not be hot if u bought it..
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
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
Hi!
With a power dissipation of 0.35 Watt your LM317/TO220 doesn't need a heat sink.
1.9 watt is the maximum power dissipation of the LM317/TO220 without a heat sink.Code: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
(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
The 13.5 volt (Vpp) is only a reference voltage, the PIC generates it's own internal
programming voltage. Therefore the current of 140 mA is drawn also from the 5V regulator.
(In reality it is less than 140 mA because some current is used by the programming LED).
The LM7805/TO220 Rja value is 50 °C/W and its TjMAX is 125 °C.
(Same as the LM317/TO220, see previous post).
The input voltage of the LM7805 is 13.5V (verify that) and the output voltage is 5V.
The voltage difference is 8.5V. (13.5V - 5V).
The current is 140mA when programming and 40mA when not programming.
When programming, the power dissipation of the LM7805 is:
8.5V * 0.14 = 1.19 Watt
When not programming, the power dissipation of the LM7805 is:
8.5V * 0.04 = 0.34 Watt
For the LM7805/TO220 the power dissipation is most of the time 0.34 Watt so
there is no need for a heat sink.
Luciano
mine always gets hot. not hot enough to burn my fingers... but i cant feel heat in the tips of my fingers anymore. haha
I have also had to replace the '7407 a couple of times.
other than thats its been ok... one thing though. never leave it plugged in if youre not using it esp. if you just turned on your computer and havent run the epic software yet.