Relay Arc Supression Circuit

[[email protected]]

I have the following circuit:

+5Vdc
|
+---------------+------------------------+
| | |
| | |
330 Ohm Diode |
| | |
| | 5Vdc Relay Coil
| | |
LED 5.1V Zener |
| | |
| | |
| | |
+---------------+------------------------+
|
|
+---+---+
To Micro----1kohm--+B C |Transistor
| E |
+---+---+
|
|
|
GND


I'm concerned about reverse bias on the LED when the realy lets go. I
measure about 7.5 Vdc across the LED when the relay lets go. I think
the zener and the diode act as a good method to handle the coil
magnetic field collapse and ensure fast armature motion but I do
violoate the 5 Vdc LED reverse bias voltage. Any comments or
suggestions for this circuit? I need to maintain the LEDs for
visibility and troubleshooting. I'm hoping this thread discusses some
general techniques for realy arc supression and addresses the LED in
this specific example.

Thanks!

 

[Ian Stirling]

I have the following circuit:

+5Vdc
|
+---------------+------------------------+
| | |
| | |
330 Ohm Diode |
| | |
| | 5Vdc Relay Coil
| | |
LED 5.1V Zener |
| | |
| | |
| | |
+---------------+------------------------+

Why diode in series with the zener?

Anyway.
Remove the diode and zener, place across the LED.

Or actually, an ordinary diode across the LED.
Turns off, and relay coil switches ends, and the 330 ohm resistor is
used as a snubber to absorb the energy.
Depends on the ratio between the 330 ohm and the relay coil impedence,
and the Vce of the transistor.

 

[Frank Bemelman]

I have the following circuit:

+5Vdc
|
+---------------+------------------------+
| | |
| | |
330 Ohm Diode |
| | |
| | 5Vdc Relay Coil
| | |
LED 5.1V Zener |
| | |
| | |
| | |
+---------------+------------------------+
|
|
+---+---+
To Micro----1kohm--+B C |Transistor
| E |
+---+---+
|
|
|
GND


I'm concerned about reverse bias on the LED when the realy lets go. I
measure about 7.5 Vdc across the LED when the relay lets go. I think
the zener and the diode act as a good method to handle the coil
magnetic field collapse and ensure fast armature motion but I do
violoate the 5 Vdc LED reverse bias voltage. Any comments or
suggestions for this circuit? I need to maintain the LEDs for
visibility and troubleshooting. I'm hoping this thread discusses some
general techniques for realy arc supression and addresses the LED in
this specific example.

 

[John Popelish]

I have the following circuit:

+5Vdc
|
+---------------+------------------------+
| | |
| | |
330 Ohm Diode |
| | |
| | 5Vdc Relay Coil
| | |
LED 5.1V Zener |
| | |
| | |
| | |
+---------------+------------------------+
|
|
+---+---+
To Micro----1kohm--+B C |Transistor
| E |
+---+---+
|
|
|
GND


I'm concerned about reverse bias on the LED when the realy lets go. I
measure about 7.5 Vdc across the LED when the relay lets go. I think
the zener and the diode act as a good method to handle the coil
magnetic field collapse and ensure fast armature motion but I do
violoate the 5 Vdc LED reverse bias voltage. Any comments or
suggestions for this circuit? I need to maintain the LEDs for
visibility and troubleshooting. I'm hoping this thread discusses some
general techniques for realy arc supression and addresses the LED in
this specific example.

Thanks!

I would try this:
+5Vdc
|
+---------------+------------------------+
| | |
| | |
330 Ohm Diode |
| | |
| +---------+ 5Vdc Relay Coil
| | | |
LED | 5.1V Zener |
| | | |
| | | |
| | | |
+-----+ +------------------------+
|
|
+---+---+
To Micro----1kohm--+B C |Transistor
| E |
+---+---+
|
|
|
GND

 

[John_H]

I have the following circuit:

I'm concerned about reverse bias on the LED when the realy lets go. I
measure about 7.5 Vdc across the LED when the relay lets go. I think
the zener and the diode act as a good method to handle the coil
magnetic field collapse and ensure fast armature motion but I do
violoate the 5 Vdc LED reverse bias voltage. Any comments or
suggestions for this circuit? I need to maintain the LEDs for
visibility and troubleshooting. I'm hoping this thread discusses some
general techniques for realy arc supression and addresses the LED in
this specific example.

Thanks!

Do you feel the Zener voltage is important? I only ever used simple diodes
across the relay coil. The voltage is quite a bit smaller to collapse the
magnetic field, but how long do you believe that collapse will take driven
into 0.7V? If the zener is removed, the LED is protected. If you change to
a 3.3V zener, your reverse voltage will hit about 5V - on the edge, but
better. If you feel strongly that the zener is needed, I like Ian
Stirling's idea of the doide across the LED which also gives you a snubber
resistor.

 

[[email protected]]

The LED is supposed to be on when the transistor provides a ground
showing that the relay is active. Wouldn't this connection reverse
bias the zener (acutally it would foward bias it but zeners are
normally used in reverse bias). So I don't think the LED would
function properly.

Thanks!

 

[[email protected]]

If you have time visit:
http://relays.tycoelectronics.com/app_pdfs/13c3236.pdf
and go to page 3 "Other Arc Supression Methods."

This is where I based the zener diode in series decision. Could you
point me to a better reference? The article above will discuss the
diode sereis resistor method you mention as well but concludes a zener
is a better way to go for minimizing hold up time. I'm certain this
type of circuit is done routinely so any other resources would be
great.

Thanks for your time!

 

[[email protected]]

Hmmm, I'm no expert at all. That said, enlighten me! I thought the
rule of thumb was to target a zener voltage near the realy coil voltage
(5Vdc). I think the gist is that this will effectively start the
magnetic collapse sooner and provide a path for a 5.1 + 0.7 amount on
energy absoprtion back to the rail. If you go to high, it never
activates as the zener knee voltage is not met. If you go too low you
don't get the benefit of the zener and it acts more like a solo diode.
When both are in play, this aids in releasing the armature more
quickly. The load on the contact side of the realy is another realy
coil which drives an inductive laod.

Thanks for your time!

 

[Spehro Pefhany]

If you have time visit:
http://relays.tycoelectronics.com/app_pdfs/13c3236.pdf
and go to page 3 "Other Arc Supression Methods."

This is where I based the zener diode in series decision. Could you
point me to a better reference? The article above will discuss the
diode sereis resistor method you mention as well but concludes a zener
is a better way to go for minimizing hold up time. I'm certain this
type of circuit is done routinely so any other resources would be
great.

Thanks for your time!

"For those applications that cannot tolerate lengthened hold-up time,
a resistor may be placed in series with the diode. The resistor does,
however, lessen the effectiveness of the diode and, usually, a
compromise must be reached by trial and error."

That is so sad.


Best regards,
Spehro Pefhany

 

[John_H]

If you have time visit:
http://relays.tycoelectronics.com/app_pdfs/13c3236.pdf
and go to page 3 "Other Arc Supression Methods."

This is where I based the zener diode in series decision. Could you
point me to a better reference? The article above will discuss the
diode sereis resistor method you mention as well but concludes a zener
is a better way to go for minimizing hold up time. I'm certain this
type of circuit is done routinely so any other resources would be
great.

Thanks for your time!

Is holdup time an issue for you? We never had a need for 2 ms vs 9 ms.
see: http://relays.tycoelectronics.com/app_pdfs/13c3311.pdf

Would you mind providing a link to the relay you're using? (to help
determine holdup time)

Are you running a high voltage through the relay contacts such that contact
arcing is your big concern?

 

[John_H]

Hmmm, I'm no expert at all. That said, enlighten me! I thought the
rule of thumb was to target a zener voltage near the realy coil voltage
(5Vdc). I think the gist is that this will effectively start the
magnetic collapse sooner and provide a path for a 5.1 + 0.7 amount on
energy absoprtion back to the rail. If you go to high, it never
activates as the zener knee voltage is not met. If you go too low you
don't get the benefit of the zener and it acts more like a solo diode.
When both are in play, this aids in releasing the armature more
quickly. The load on the contact side of the realy is another realy
coil which drives an inductive laod.

Thanks for your time!

By using a 3.3V Zener instead of 5.1V, you have a Zener + Diode reverse
voltage maximum of about 5V instead of your measured 7.5V. The Zener plus
diode at highest current gives you the max reverse voltage for your LED.

If you want to use the Zener because you feel the reduced holdup is
important, consider a higher voltage zener and either 1) a diode reversed
across the LED or 2) a cap across the LED that just needs to keep the
reverse voltage from getting to 5V during the coil discharge.

 

[John Fields]

I have the following circuit:

+5Vdc
|
+---------------+------------------------+
| | |
| | |
330 Ohm Diode |
| | |
| | 5Vdc Relay Coil
| | |
LED 5.1V Zener |
| | |
| | |
| | |
+---------------+------------------------+
|
|
+---+---+
To Micro----1kohm--+B C |Transistor
| E |
+---+---+
|
|
|
GND


I'm concerned about reverse bias on the LED when the realy lets go. I
measure about 7.5 Vdc across the LED when the relay lets go. I think
the zener and the diode act as a good method to handle the coil
magnetic field collapse and ensure fast armature motion but I do
violoate the 5 Vdc LED reverse bias voltage. Any comments or
suggestions for this circuit? I need to maintain the LEDs for
visibility and troubleshooting. I'm hoping this thread discusses some
general techniques for realy arc supression and addresses the LED in
this specific example.

---


+V---+-------------+
| |
[300R] |
| [COIL]
[LED] |
| |
+--[1N4148>]--+-+-----+
| |
C |K
µC>-------[1KR]----B [ZENER]
E |
| |
GND>-----------------+-----+

Choose the Zener voltage to get the armature release speed you need
commensurate with not zapping the transistor, and use the 1N4148 to
keep from reverse biasing the LED.

 

[[email protected]]

The LED is supposed to be on when the transistor provides a ground
showing that the relay is active. Wouldn't this connection reverse
bias the zener (acutally it would foward bias it but zeners are
normally used in reverse bias). So I don't think the LED would
function properly.

You didn't show the cathodes of the diode or zener, so I made some
assumptions.

I assumed that the cathode of the diode is at top, and cathode of zener
is at bottom.

So the LEd would be on when the transistor is on, through the forward
biased zener.

At turn off, the top diode is forward biased (while the inductance
discharges through the two diodes), so the LED sees no more reverse
voltage than than the top diode's forward drop.

 

[[email protected]]

Hmmmm, so the zener sinks the stored energy at relay releae to GND in
this design. How would you recommend the sizing of the zener? I
surmise it would be < Vce max of the transistor? Doesn't this present
a similar problem as I have with the reverse bias on the LED? What I
mean is, the zener will clamp to some V but suppose the stored energy
is >> V then the transistor could be zapped anyway, right? And of
course the diode doesn't relate to the stored energy in this design
except for blocking any current during stored energy release.

Thanks for your time.

 

[John Fields]

Hmmmm, so the zener sinks the stored energy at relay releae to GND in
this design. How would you recommend the sizing of the zener? I
surmise it would be < Vce max of the transistor? Doesn't this present
a similar problem as I have with the reverse bias on the LED? What I
mean is, the zener will clamp to some V but suppose the stored energy
is >> V then the transistor could be zapped anyway, right? And of
course the diode doesn't relate to the stored energy in this design
except for blocking any current during stored energy release.

Thanks for your time.

---
To what article and to whom are you responding?

Read this, From:

http://groups.google.com/support/bin/answer.py?answer=12348&topic=250

"Summarize what you're following up.

When you click "Reply" under "show options" to follow up an existing
article,
Google Groups includes the full article in quotes, with the cursor
at the top
of the article. Tempting though it is to just start typing your
message,
please STOP and do two things first. Look at the quoted text and
remove parts
that are irrelevant. Then, go to the BOTTOM of the article and start
typing there.
Doing this makes it much easier for your readers to get through your
post.
They'll have a reminder of the relevant text before your comment,
but won't have to re-read the entire article. And if your reply
appears on a site
before the original article does, they'll get the gist of what
you're talking about."

 

[Frank Bemelman]

Hmmmm, so the zener sinks the stored energy at relay releae to GND in
this design. How would you recommend the sizing of the zener? I
surmise it would be < Vce max of the transistor? Doesn't this present
a similar problem as I have with the reverse bias on the LED? What I
mean is, the zener will clamp to some V but suppose the stored energy
is >> V then the transistor could be zapped anyway, right? And of
course the diode doesn't relate to the stored energy in this design
except for blocking any current during stored energy release.

Use what John Popelish told you. You obviously don't have a clue
about diodes and zeners, so take the advice and stop questioning.

 

[[email protected]]

The 3.3 is my punt plan for the current artwork or to populate a 0 ohm
resistor where the zener is.

Here's what I'm not understanding...with the 5.1 zener and per my
o'scope, it appears the worst case reverse bias on the LED is 7.5 as I
aforementioned and I see about 3V across the series resistor, Rs. So
this sums to ~10.5 Vdc. So does the 5V rail + 5.1 (zener) + 0.7
(diode) create a voltage of about 10.8 reverse bias? This seems wrong
to me as the 5V rail is fixed but empirically the 10.5 is close to the
10.8. So, in my stupidity, I changed the value of Rs (reduced it as I
could afford to have more current run through the LED in normal
operation) but duh, the I-V charactereistics of the LED in reverse bias
pretty much fix the voltage drop across Rs. So I think your statment
about 5.1 + the diode drop at worst current must be what is yielding
the ~10.5 Vdc I see across the LED and Rs. Is that correct? Will the
diode/zener deviate that much from the nominal 5.1 + 0.7? Also, in
your experience, if this relay swithces slowly, would a diode by itself
be adeuqate? It only runs the coild of an offboard realy and is
switching 24AC to this other realy. I know some of these are basic
questions but I appreciate your input.

Thanks again for your time.

 

[[email protected]]

To what article and to whom are you responding?

Read this, From:

http://groups.google.com/support/bin/answer.py?answer=12348&topic=250

RTFMed, thanks for that. I'd been using the reply at the bottom of the
post and by default no text is included whatsoever. Sorry for the
confustion I rarely use the web interface and usually use Knode to
post...my bad.

 

[John Fields]

Hmmmm, so the zener sinks the stored energy at relay releae to GND in
this design. How would you recommend the sizing of the zener? I
surmise it would be < Vce max of the transistor? Doesn't this present
a similar problem as I have with the reverse bias on the LED? What I
mean is, the zener will clamp to some V but suppose the stored energy
is >> V then the transistor could be zapped anyway, right? And of
course the diode doesn't relate to the stored energy in this design
except for blocking any current during stored energy release.

---
Huh???

Go to:

http://www.linear.com/designtools/softwareRegistration.jsp

download the simulator, and run this:

Version 4
SHEET 1 880 680
WIRE -384 176 -384 64
WIRE -384 320 -384 176
WIRE -384 416 -384 400
WIRE -352 176 -384 176
WIRE -208 176 -272 176
WIRE -112 320 -112 288
WIRE -112 416 -384 416
WIRE -112 416 -112 400
WIRE -48 288 -112 288
WIRE 16 176 -144 176
WIRE 80 288 32 288
WIRE 144 176 80 176
WIRE 144 176 144 144
WIRE 144 192 144 176
WIRE 144 240 144 192
WIRE 144 416 -112 416
WIRE 144 416 144 336
WIRE 208 64 -384 64
WIRE 208 144 144 144
WIRE 272 192 144 192
WIRE 272 272 272 192
WIRE 272 416 144 416
WIRE 272 416 272 336
WIRE 272 448 272 416
FLAG 272 448 0
SYMBOL npn 80 240 R0
SYMATTR InstName Q1
SYMATTR Value 2N4401
SYMBOL ind 192 48 R0
SYMATTR InstName L1
SYMATTR Value .1
SYMATTR SpiceLine Rser=100
SYMBOL zener 288 336 R180
WINDOW 0 -42 32 Left 0
WINDOW 3 -120 0 Left 0
SYMATTR InstName D1
SYMATTR Value BZX84C15L
SYMBOL diode 16 192 R270
WINDOW 0 32 32 VTop 0
WINDOW 3 0 32 VBottom 0
SYMATTR InstName D2
SYMATTR Value 1N4148
SYMBOL res -256 160 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R1
SYMATTR Value 300
SYMBOL voltage -112 304 R0
WINDOW 3 -152 153 Left 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR Value PULSE(0 5 .1 1e-6 1e-6 .1 .2 3)
SYMATTR InstName V1
SYMBOL voltage -384 304 R0
WINDOW 3 -6 144 Left 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR Value 5
SYMATTR InstName V3
SYMBOL LED -208 192 R270
WINDOW 0 72 32 VTop 0
WINDOW 3 0 32 VBottom 0
SYMATTR InstName D3
SYMATTR Value QTLP690C
SYMBOL res 48 272 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R2
SYMATTR Value 1000
TEXT -418 506 Left 0 !.tran 1

 

[[email protected]]

To what article and to whom are you responding?

Read this, From:

http://groups.google.com/support/bin/answer.py?answer=12348&topic=250

RTFMed, thanks for that. I'd been using the reply at the bottom of the
post and by default no text is included whatsoever. Sorry for the
confustion I rarely use the web interface and usually use Knode to
post...my bad.