Thermal out problem
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Posts: 46,084
From: "Michael Hendricks" <mjh80@b...>
Subject: Voltage Regulators thermaling out
I have a circuit that is running at about 300ma draw. We are using a 1Amp 7508.
The circuit is in an enclosed case and after about 5-10 minutes the 7805 gets
too hot and shuts down. It "cuts" for about 20ms but that is long enough to
reset the stamp. are there any ideas on keeping the 7805 cool? Since it is in an
enclosed box adding a heat sink didnt help much. We have also tried using 3amp
and 5amp versions but with the same results. Thank you for any assistance.
MH
Hi Mike:
Try turning down the input voltage into the device. The regulator will dissipate
power as a function of the voltage drop through it times the load current. If
you are running on batteries or cannot change the voltage level for any other
reason, insert a series resistor to drop the input voltage to the regulator to
about 8 volts at the rated load current. When sizing this power resistor, take
the calculated dissipated power and then double that number. You will probably
find that you will need a 10 - 20W resistor (depending on the voltage level).
If you need more info, please let me know.
Gerry Shand
gerry_shand@t...
Subject: Voltage Regulators thermaling out
I have a circuit that is running at about 300ma draw. We are using a 1Amp 7508.
The circuit is in an enclosed case and after about 5-10 minutes the 7805 gets
too hot and shuts down. It "cuts" for about 20ms but that is long enough to
reset the stamp. are there any ideas on keeping the 7805 cool? Since it is in an
enclosed box adding a heat sink didnt help much. We have also tried using 3amp
and 5amp versions but with the same results. Thank you for any assistance.
MH
Hi Mike:
Try turning down the input voltage into the device. The regulator will dissipate
power as a function of the voltage drop through it times the load current. If
you are running on batteries or cannot change the voltage level for any other
reason, insert a series resistor to drop the input voltage to the regulator to
about 8 volts at the rated load current. When sizing this power resistor, take
the calculated dissipated power and then double that number. You will probably
find that you will need a 10 - 20W resistor (depending on the voltage level).
If you need more info, please let me know.
Gerry Shand
gerry_shand@t...