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
MH
Comments
If your box is metal, preferably aluminum, You bolt the regulator tab to the
case. Usually, you have to use insulated mounting because the tab is
connected to one of the regulator pins. Thermal grease can be used for
better conduction.
If the case is non-metallic, an external power resistor can sometimes be
used to decrease the voltage that the regulator must drop, depending on load
and input voltage.
Ray McArthur
Original Message
From: Michael Hendricks <mjh80@b...>
To: <basicstamps@egroups.com>
Sent: Tuesday, November 14, 2000 12:18 AM
Subject: [noparse][[/noparse]basicstamps] 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
What is your input voltage?
For each 3.3v difference with the 5v output, you get 1 watt dissipation.
Let assume that the input is at 12v, you stoke 2.1 watt in the regulator. This is sufficient to make it very hot if not cooled.
Original Message
From: Michael Hendricks
To: basicstamps@egroups.com
Sent: mardi 14 novembre 2000 06:18
Subject: [noparse][[/noparse]basicstamps] 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
MH
Original Message
From: ECO
To: basicstamps@egroups.com
Sent: Tuesday, November 14, 2000 4:30 AM
Subject: Re: [noparse][[/noparse]basicstamps] Voltage Regulators thermaling out
Michael
What is your input voltage?
For each 3.3v difference with the 5v output, you get 1 watt dissipation.
Let assume that the input is at 12v, you stoke 2.1 watt in the regulator. This is sufficient to make it very hot if not cooled.
Original Message
From: Michael Hendricks
To: basicstamps@egroups.com
Sent: mardi 14 novembre 2000 06:18
Subject: [noparse][[/noparse]basicstamps] 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
The 7805 is a very cheap regulator, which is why it is used so often,
however for some projects, a better, yes more expensive regulator is
to be preferred. For most of my projects I use Power Trends Switching
Regulators. They are made to replace 7805's and do a wonderful job of
taking up to 30 volts and giving a flat 5.000 with little to no heat.
Digi-key has them. IF the project can accept some cost increase this
is a wonderful solution.
Just a suggestion,
Ron A.
--- In basicstamps@egroups.com, "Michael Hendricks" <mjh80@b...>
wrote:
> 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
but I suspect that will change soon. They are much larger, and they are
switchers, so they are noiser, but because they are switchers they are very
efficient and very little heat even when converting 28V to 5V. Be sure to
leave lots of room on the board.
Regards,
Al Williams
AWC
*Floating point math for the Stamp, PIC, SX, or any microcontroller at
http://www.al-williams.com/awce/pak1.htm
>
Original Message
> From: ronaldsa@e... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=QmqwRjDDV3h21GaxdIo_5TaTgRrPRDO1NQ7ssz2HIW_VnKAohjyz1k1r-awjJ7hRCJ4G-F_MPvMvV-327A]ronaldsa@e...[/url
> Sent: Tuesday, November 14, 2000 8:39 AM
> To: basicstamps@egroups.com
> Subject: [noparse][[/noparse]basicstamps] Re: Voltage Regulators thermaling out
>
>
>
> Micheal,
>
> The 7805 is a very cheap regulator, which is why it is used so often,
> however for some projects, a better, yes more expensive regulator is
> to be preferred. For most of my projects I use Power Trends Switching
> Regulators. They are made to replace 7805's and do a wonderful job of
> taking up to 30 volts and giving a flat 5.000 with little to no heat.
>
> Digi-key has them. IF the project can accept some cost increase this
> is a wonderful solution.
>
> Just a suggestion,
>
> Ron A.
>
>
> --- In basicstamps@egroups.com, "Michael Hendricks" <mjh80@b...>
> wrote:
> > 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
>
>
>
Do you have a capacitor to ground on the output pin3 of the 7805?
Experiment with different values. This may help with the 20ms drop-out.
Also, you may consider enclosing your project in a metal box and bolt the
7805 to the inside of the box. This will act as a big heat sink.
--- Michael Hendricks <mjh80@b...> wrote:
> 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
> didn't help much. We have also tried using 3amp and 5amp versions but
> with the same results. Thank you for any assistance.
>
> MH
>
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