Best way to suppres inductor(relay coil) transients?

[seyyah]

mov diode inductive kickback

I am using diodes for suppressing these transients. But sometimes it is not enough. What can be done for better suppressing. I think there are zener-zener, zener-diode.. choices? which one is better and how to choose zener? Does it make sense to connect parallel capacitor across the relay coil? If so how will i decide the value of cap? I must suppress it as possible as i can.

 

[seyyah]

cap across relay coil

I also want to ask that faster diodes like uf1007 can supply better suppression than slower ones like 1n4007?

 

[alphi]

relay coil transients

Do you use it in switching mode power supply?
for smps:
in small power,1N4007 is better than UF4007,but it have more loss,so it can not use in large power.

 

[flatulent]

rc snubber 48v ac

The diode method produces the least increase in voltage. The diode should be rated for a current equal to the operating coil current. Faster response is better. usually a small signal silicon is used. https://www.fairchildsemi.com/ds/1N/1N4148.pdf is for the 1N918 and 1N4148.

 

[Regnum]

relay coil snubber zener diode

I assume you've already placed bypassing capacitors from VCC to GND as close as possible to the relay-coil and its driver...?
There are several factors that determine the effectiveness of the transient-suppressing diode, such as forward recovery characteristic, lead inductance and parasitic series inductances. Personally, I never had to use diodes faster than 1N4007 for relay-coil transient suppressing... What relay are you using...? Are you driving it with BJTs or MOSFETs... ?
You should try RC snubbers, or RC clamp networks rather than connecting capacitors to the coil.

 

[bbarney]

how to isolate relay coil noise

could you elaborate on what an rc snubber is because i have a friend with these same problems(newbie)

 

[Regnum]

what does an inductor do in a relay

These are four different approaches.
For relay-coil clamps configuration #1 is almost always enough. Check bypassing / decupling / layout issues.

 

[ee_wmkab]

best ways to drive the relay

I have encountered this kind of problem before.
I used RC snubber and a diode in parallel with coil. It can reduce the tranisients of the relay coil during on/off.

What is your application (AC or DC)?
If you are using the coil in AC circuit. A snubber and diode is a must. Otherwise, the contact of the relay will become bad contact (due to sparking).

If you find the transients greatly affect the stability of your system, you should better use a separate power supply for the coil path.

BR
Keith

 

[seyyah]

bypass capacitor across relay

I'm using relays in a dc application not an smps. They are operated at 48VDC and i'm using bjt's to drive them. Is using mosfet better tan bjt?
And look at the drawings please. Which configuration can help me more?

 

[Regnum]

inductor on relay supply

I'd like to know how you do perceive the problem...
Some logic circuitry crashes as operating relays, or transistors break?

Is using mosfet better tan bjt?

The high di/dt of MOSFETs would make it worse

Which configuration can help me more?

Forget about scheme #2... you dont want such a high current flowing through the capacitor when transistor turns on.

In schemes 1, 2 and 4, see that you're clamping the collector to [Vcc + Vz] volts, so It could be breaking the transistors. (What's the sense of those zener diodes...?)

Regarding scheme #3, it may be OK but it's more orthodox using the scheme #1 of my drawings

Once again, check bypassing, decoupling, and PCB layout issues.

-Always use bypass capacitors from the VCC terminal of relay to the transistor emitter.
-Always use decoupling circuitry from Relays-VCC to Logic-VCC (LC-networks, and separated voltage regulators)
-Always use star schemes for GND and VCC routing (don't ever return the relays current trough the logic GND; do it directly to power supply GND point)

 

[rauol]

inductor relay

Use a transient voltage suppressor and MOV

 

[seyyah]

what is inductor relay

I'd like to know how you do perceive the problem...
Some logic circuitry crashes as operating relays, or transistors break?

Yes when relays turned off, sometimes logic circuit fails but bjt's are ok.

In schemes 1, 2 and 4, see that you're clamping the collector to [Vcc + Vz] volts, so It could be breaking the transistors. (What's the sense of those zener diodes...?)

I actually don't know exactly how zener would help. I saw it in a relay manufacturer's web page. They are suggesting a zener-diode or zener-zener connected across the realy coil for suppressing.

Regarding scheme #3, it may be OK but it's more orthodox using the scheme #1 of my drawings

I'm using also the number 1 scheme of your drawings. But i am still facing problems so i want to know that can i improve it?

-Always use bypass capacitors from the VCC terminal of relay to the transistor emitter.

So i'will use No1 of your drawings and add a cap across the relay's pozitive terminal and emitter. Right?

-Always use decoupling circuitry from Relays-VCC to Logic-VCC (LC-networks, and separated voltage regulators)

It is difficult to use L for now. Because I'm trying to solve the problem of a finished design. I'm rather restricted to make major changes. Using LC may be done in the rev2 after solving the problems of rev1. I'm using various capacitors for decoupling. Also logic and relay circuitry has different supplies but their ground is common.

-Always use star schemes for GND and VCC routing (don't ever return the relays current trough the logic GND; do it directly to power supply GND point)

Actually i badly done this mistake before. Then i tried to fix it. But as i said before i'm restricted to change freely everything. But after solving these problems, i will try to do a better pcb design and i will seperate logic and relay type noise circuitry as possible as i can.

 

[seyyah]

best mov for 120vac coil

Use a transient voltage suppressor and MOV

For example what? (and how?)
What is MOV? (metal oxide varistor?)

 

[Regnum]

relay coil snubbers

Varistors are more suitable for supressing transients at relay contacts (specially when they're driving inductive loads). But you're asking about COIL transients...

...logic and relay circuitry has different supplies but their ground is common...

...But after solving these problems, i will try to do a better pcb design...

...maybe you won't solve it till you improve the PCB :!:

 

[Ante]

zener coil relay contact

Seyyah,

A diode / capacitor combination is the most effective if the correct values are chosen.

Ante :roll:

 

[Regnum]

inductor kickback suppressor

Try this choice

good luck

 

[seyyah]

bypass diode relay coil

Try this choice

good luck

I used a diode/capacitor+resistor combination and separated the logic circuit better than before. It's now in test and seems good until now. But i'll also keep your suggestion in mind. After now i'll first design the relay circuit. Can you explain what D1 diode does and how to choose varistor? I didn't use varistor before?

 

[guyaneseboy]

Use a seperate supply to drive the relay coil and use an optocoupler to drive the BJT. Do not forget the free wheeling diode to supress inductive kickback ( across the BJT collector to the relay positive supply as previously mentioned). The return ground(s) for the logic circuit and relay
should be a single (star) connection at the regulator.

Good luck
Guyaneseboy

 

[hock]

the best way is to use tranzorb.
they have switching times of the order of ns.
hock

 

[Regnum]

fellas,

I feel like trying to kill a roach with a sort of last-generation missile...

IMHO all we need is a silicon diode for avoiding to fry the BJT, and a sharp layout to prevent logic from crashing.

hugs,
Regnum