I am pulsing a 38mH coil (16 AWG wire wrapped around a small tube) with a IRFB4115pbf MOSFET at 66.6v (3 lipo 5200mAH "50C" battery's in series). It's a lot of juice! Using Lt spice I simulated this and found that the voltage spikes can reach up to 20kv. I am trying to figure out if I should use a flyback diode across the coil, or a RC snubber to absorb the the extra voltage.
Iv'e been using a 10 amp diode as a flyback for testing and it seems to work just fine, but I've heard an RC snubber works better.

Which one should I use???

 

Which one should I use???

A snubber will likely cause the coil current to decay faster, if that's a consideration.
But the snubber R and C values must be properly selected to give a damped response with the maximum voltage you want.

 

A snubber will likely cause the coil current to decay faster, if that's a consideration.
But the snubber R and C values must be properly selected to give a damped response with the maximum voltage you want.

Yes, I would like the coil to be de-energized as fast as possible.
Thanks for the response!

 

I would like the coil to be de-energized as fast as possible.

Then the fastest is a Zener with the breakdown voltage of the flyback voltage you can tolerate in inverse series with the diode.

 

Then the fastest is a Zener with the breakdown voltage of the flyback voltage you can tolerate in inverse series with the diode.

What would be the best option for both fastest turn on and off of coil?

 

it is the release time that is affected by snubber...
and as stated - use zener... (in anti-series series with regular diode or another zener)

this allows you to select breakdown voltage your circuit can tolerate. for example you have a relay driven by transistor that has breakdown voltage 60V. you can pick zener that is under that 60V limit of transistor (so transistor survives). the higher the voltage the larger the spike and shorter the release time... so... nothing stops you from using transistor rated for 450V and zener for 400V...

 

What would be the best option for both fastest turn on and off of coil?

The turn on time is determined by the applied coil voltage.

The fastest turn-off would be the diode-Zener combination, which would be determined by the Zener voltage and how much voltage the control switch can tolerate.

 

Don't forget that the initial current through the zener will be the same as the coil current at the point of switch-off.
The maximum power dissipated in the zener will be the zener voltage multiplied by the initial current.

 

The maximum power dissipated in the zener will be the zener voltage multiplied by the initial current.

And the total energy dissipated in the Zener will be near the energy stored in the inductance.

 

And the total energy dissipated in the Zener will be near the energy stored in the inductance.

And that is true regardless of the method of damping.
Power x time = energy
and initial power is proportional to zener or diode voltage.
So the reduction in de-energising time will be approximately in proportion to the zener voltage divided by the diode voltage.
(The resistance of the inductor comes into it as well, but that is assumed to be small)

 

What would be the best option for both fastest turn on and off of coil?

This circuit can produce short (2 ms), powerful (P_amp=13 kW) current pulse through coil:

For details see https://forum.allaboutcircuits.com/...-gauge-for-pulses-current.189436/post-1768216

 

First, what is the rate of change of that coil current? And what is the purpose of the pulsing??? Slowing the falll time will reduce that pulse voltage quite a lot.So that might reduce the problem.

 

First, what is the rate of change of that coil current? And what is the purpose of the pulsing??? Slowing the falll time will reduce that pulse voltage quite a lot.So that might reduce the problem.

This circuit is a coil gun, so the purpose of pulsing is to launch a metal projectile. The fall time of the mosfet is pretty much at the best it can be, mosfet driver circuit, plus low value gate resistor, ect.

 

Hi E76.
Coil guns are not allowed on AAC.. This Thread is Closed.


Moderation