voltage spike circuit resolution needed

[robismyname]

The following circuits generates the attached waveform attached. I would like to remove the large voltage spikes but not sure what will work. How should i think of mitigating the voltage spike? Waveform and schematic is attached.

 

[Raza]

Can you uplaod a better image, as the attached image is not showing the spikes clearly.

 

[FvM]

The circuit seems confused in several points, how's the solenoid connected, what's the meaning of the strange FET connections? I guess, you are actually talking about the ignition module from your previous post. Unfortunately, you also didn't manage to clarify, how the circuit has been connected. Several experienced forum members tried to help and finally gave up.

https://www.edaboard.com/threads/223257/

The most likely interpretation in my view has been, that you are not driving the real coil but a control input of the module. In this case, the spike would be just a measurement artefact. But there should be no problem to clamp it with a zener diode near the MOSFET.

The real ignition coil has a "spike" of at least 300 to 400 V at it's primary that can't be surpressed without affecting the ignition operation.

 

[robismyname]

Can you uplaod a better image, as the attached image is not showing the spikes clearly.

Ok please check images now. This is not related to ignition coil post.

 

[FvM]

This is not related to ignition coil post.

O.K. it seemed so to me. To refer to what's already said. If the transistor is driving a coil, a spike or inductive "kickback" is normal operation. It depends on the purpose of the coil and also the stored energy, if and how it can be supressed. A standard method is to connect a "free-wheeling" diode across the coil. As a disadvantage, it slows down the decay of coil current, unwanted in some situations. Alternative, a Z-diode can be placed in parallel to the transistor. The zener voltage must be above the supply voltage.

If the circuit is not directly driving a coil, the suggested circuits can reduce voltage peaks anyway.

 

[robismyname]

Alternative, a Z-diode can be placed in parallel to the transistor. The zener voltage must be above the supply voltage.

Yes I used the zener. The zener is successful in reducing the voltage spike (see attached). Is there anything else I can do to smooth out the ripples. Im think like a .01uf cap

 

[dick_freebird]

Look for "snubber". Cap plus a resistor that dissipates the
inductor stored energy. Makers of solenoids and relays often
have app notes on selecting snubber values.

 

[FvM]

Is there anything else I can do to smooth out the ripples.

The waveform looks quite acceptable in my view. No reason to add additional circuits normally.

 

[robismyname]

The zener voltage must be above the supply voltage.
If the circuit is not directly driving a coil, the suggested circuits can reduce voltage peaks anyway.

Out of curiosity i disconnected the resistor (10 ohms) to see if the solenoid could make a 12 volt rail. It doesnt. Shouldn't the solenoid create a 12 volt rail when the fet gate is tied to ground? I have noticed even if the gate is high (3V) or low (grounded) that the rail without the resistor always read 0 V. Am i misinterpreting the function of a solenoid?

 

[FvM]

Any solenoid I know is behaving different from yours. Sounds more like a loose cable.

Solenoids have a specified resistance, and there are simple means to check it.