Protection Diodes
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Posts: 46,084
Earlier, Dave Mucha stated I could use Diodes in order to protect my ULN2803
from reverse polarity. I've looked at a couple of different ways but wasn't
able to get it to work.
24 vdc +
TB
2803
TB
24 vdc is on board and goes to Terminal #1
Terminal #2 goes to the 2803 and sinks to ground when activated
Relay or Light across TB's is energized.
"How" can a diode be inserted in there to protect the 2803 in case 24 dc is
put directly on Terminal #2. Looks like it would be a dead short.
24vdc
>|---- TB1
2803
|<
TB2
That there doesn't do any good, it allows current to flow directly to
ground.
24vdc
>|---- TB1
2803
>|---- TB2
Like the above, the circuit would never function would it?
Dave mentions 4 diodes, but I wouldn't have a clue where to put 4 diodes.
from reverse polarity. I've looked at a couple of different ways but wasn't
able to get it to work.
24 vdc +
TB
2803
TB
24 vdc is on board and goes to Terminal #1
Terminal #2 goes to the 2803 and sinks to ground when activated
Relay or Light across TB's is energized.
"How" can a diode be inserted in there to protect the 2803 in case 24 dc is
put directly on Terminal #2. Looks like it would be a dead short.
24vdc
>|---- TB1
2803
|<
TB2
That there doesn't do any good, it allows current to flow directly to
ground.
24vdc
>|---- TB1
2803
>|---- TB2
Like the above, the circuit would never function would it?
Dave mentions 4 diodes, but I wouldn't have a clue where to put 4 diodes.
Comments
You might be able to use a fuse (1 amp or less) for protection. I don't
think that a diode will work in this case due to the fact that a diode
will block both voltages or let it pass.
Thanks,
Dave
Dave Andreae
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Original Message
From: Richard Skinner [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=LpG5L0BNgz9KbPRueARO3rS2WNplPQ1I4S6hMpPRKPNrQuYkjafOjlcZL806Sw50n9bOQvvnF6qCI9jUAao]rwskinner@a...[/url
Sent: Friday, June 18, 2004 1:41 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Protection Diodes
Earlier, Dave Mucha stated I could use Diodes in order to protect my
ULN2803
from reverse polarity. I've looked at a couple of different ways but
wasn't
able to get it to work.
24 vdc +
TB
2803
TB
24 vdc is on board and goes to Terminal #1
Terminal #2 goes to the 2803 and sinks to ground when activated
Relay or Light across TB's is energized.
"How" can a diode be inserted in there to protect the 2803 in case 24 dc
is
put directly on Terminal #2. Looks like it would be a dead short.
24vdc
>|---- TB1
2803
|<
TB2
That there doesn't do any good, it allows current to flow directly to
ground.
24vdc
>|---- TB1
2803
>|---- TB2
Like the above, the circuit would never function would it?
Dave mentions 4 diodes, but I wouldn't have a clue where to put 4
diodes.
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abuse@p....
some relays.
If you are not switching relays, ignore this post.
If this is true, no diodes are needed as the ULN2803 has them built in.
_http://www.mikrocontroller.net/download/uln2803.pdf_
(http://www.mikrocontroller.net/download/uln2803.pdf)
Ken
=========
Hello,
You might be able to use a fuse (1 amp or less) for protection. I don't
think that a diode will work in this case due to the fact that a diode
will block both voltages or let it pass.
Thanks,
Dave
[noparse][[/noparse]Non-text portions of this message have been removed]
polarity with a relay.
The method will also light an LED when the polarity is connected incorrectly.
If interested just say the word and I will post a schematic in the files
section.
Ken
================
Yes, I have the 2803's diodes going back to supply voltage. But we were
talking about reverse polarity, to protect the system if someone accidently
hooked 24 vdc to the terminal block, which would feed 24vdc straight to
ground via the 2803.
I was looking for a way to protect against that. I do have a fuse, but it
protects the 24 volt rail going to all the terminal blocks, and in order to
be able to carry the load for all the outputs, it has to be set at 4 amps.
Since the max load 1 pin of the 2803 can handle is 500ma, that means I'll
still probably blow the 2803 before I blow the fuse. All the traces are
.100 so they should be okay. I guess I could have installed 1/2 amp fuses
on every output but I didn't do it.
Richard
[noparse][[/noparse]Non-text portions of this message have been removed]
ken
Sure, I'd like to see it.
[noparse][[/noparse]Non-text portions of this message have been removed]
talking about reverse polarity, to protect the system if someone accidently
hooked 24 vdc to the terminal block, which would feed 24vdc straight to
ground via the 2803.
I was looking for a way to protect against that. I do have a fuse, but it
protects the 24 volt rail going to all the terminal blocks, and in order to
be able to carry the load for all the outputs, it has to be set at 4 amps.
Since the max load 1 pin of the 2803 can handle is 500ma, that means I'll
still probably blow the 2803 before I blow the fuse. All the traces are
.100 so they should be okay. I guess I could have installed 1/2 amp fuses
on every output but I didn't do it.
Richard
Original Message
From: <smartdim@a...>
To: <basicstamps@yahoogroups.com>
Sent: Friday, June 18, 2004 9:43 PM
Subject: Re: [noparse][[/noparse]basicstamps] Protection Diodes
>
> I am coming into this thread late......but if the UKL203 is used to switch
> some relays.
> If you are not switching relays, ignore this post.
>
> If this is true, no diodes are needed as the ULN2803 has them built in.
>
> _http://www.mikrocontroller.net/download/uln2803.pdf_
> (http://www.mikrocontroller.net/download/uln2803.pdf)
>
> Ken
> =========
>
> Hello,
>
> You might be able to use a fuse (1 amp or less) for protection. I don't
> think that a diode will work in this case due to the fact that a diode
> will block both voltages or let it pass.
>
> Thanks,
>
> Dave
>
>
>
>
>
> [noparse][[/noparse]Non-text portions of this message have been removed]
>
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
> Yahoo! Groups Links
>
>
>
>
>
>
> [noparse][[/noparse]Scanned by AwesomeNet Anti-Virus]
>
>
Original Message
From: <smartdim@a...>
To: <basicstamps@yahoogroups.com>
Sent: Friday, June 18, 2004 11:36 PM
Subject: Re: [noparse][[/noparse]basicstamps] Protection Diodes
>
> There is a fairly simple method to protect an entire system from reverse
> polarity with a relay.
> The method will also light an LED when the polarity is connected
incorrectly.
>
> If interested just say the word and I will post a schematic in the files
> section.
>
> Ken
>
> ================
>
> Yes, I have the 2803's diodes going back to supply voltage. But we were
> talking about reverse polarity, to protect the system if someone
accidently
> hooked 24 vdc to the terminal block, which would feed 24vdc straight to
> ground via the 2803.
>
> I was looking for a way to protect against that. I do have a fuse, but
it
> protects the 24 volt rail going to all the terminal blocks, and in order
to
> be able to carry the load for all the outputs, it has to be set at 4
amps.
> Since the max load 1 pin of the 2803 can handle is 500ma, that means I'll
> still probably blow the 2803 before I blow the fuse. All the traces are
> .100 so they should be okay. I guess I could have installed 1/2 amp
fuses
> on every output but I didn't do it.
>
> Richard
>
>
>
>
>
>
> [noparse][[/noparse]Non-text portions of this message have been removed]
>
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
> Yahoo! Groups Links
>
>
>
>
>
>
> [noparse][[/noparse]Scanned by AwesomeNet Anti-Virus]
>
>
A simple way to protect the circuit from reverse polarity is to insert a full
wave diode bridge between the input terminals. Make sure the bridge is rated
for the full current your circuit draws, and that the 1.4 volt diode drop will
not be a problem. Connect your DC input terminals to the AC legs and your
plus and minus is automatically applied to your circuit correctly. No moving
parts needed. You do not even need to mark the input + or - as the bridge takes
care of the polarity. I use this for all my industrial Stamp boards.
Thanks and good luck,
Alan Bradford
Plasma Technologies
In a message dated 6/19/2004 12:17:12 AM Eastern Daylight Time,
rwskinner@a... writes:
Yes, I have the 2803's diodes going back to supply voltage. But we were
talking about reverse polarity, to protect the system if someone accidently
hooked 24 vdc to the terminal block, which would feed 24vdc straight to
ground via the 2803.
I was looking for a way to protect against that. I do have a fuse, but it
protects the 24 volt rail going to all the terminal blocks, and in order to
be able to carry the load for all the outputs, it has to be set at 4 amps.
Since the max load 1 pin of the 2803 can handle is 500ma, that means I'll
still probably blow the 2803 before I blow the fuse. All the traces are
.100 so they should be okay. I guess I could have installed 1/2 amp fuses
on every output but I didn't do it.
Richard
[noparse][[/noparse]Non-text portions of this message have been removed]