IRF 9640 QUESTION

[daverave]

I know the irf 9640 clamps at 200V so can i still increase the tx pulse width and get more depth even though the 200v clamping has reached its max voltage ?????

[Davor]

With adequate snubber - yes.

[daverave]

pls can you explain what a snubber is and how it go's into the circuit ????

[Davor]

There are various snubbers in use. their common feature is that they clamp high voltage spikes through an appropriate resistor, so that you get precisely what you are after. Their main use is in industry where flybacks must be tamed.
Just put "snubber circuits" in google and be amazed.
I'm toying with a simple circuit right now, but with some other devious ideas on my mind

[daverave]

is there any diagrams on this site of snubber circuit for surf pi ???

[Davor]

I don't think so, but I may play with it in a day or two.
Are you familiar with LTspice?

[daverave]

i know nothing about LT spice....is it a simulator program ???

[Davor]

It is, and a popular one.
I'll try something in a day or two.

[Silver Dollar]

daverave look here to see a snubber circuit
http://www.geotech1.com/forums/attac...7&d=1405692077

It's a diode coupled RC type of thing...

[daverave]

have you tried this yet as in diagram ?????

[Silver Dollar]

Not me. I am still trying to figure out if snubbing is the way to go or allowing a big flyback voltage....

[Davor]

Avalanche is noisy, so yeah, I'm for snubbers.
The diagram in #9 is for a negative side n-channel drive, while Surf has positive side p-channel drive, so a diode in snubber must be reversed. Most probably you don't need to do anything about it.

[daverave]

are all the components in the diagram required to reduce flyback voltage....im not sure if snubber is required for IRF 740/840 as they are rated at 400 volts

[Davor]

Yes and no. Depends on what you want to achieve. My intention is to measure subtle changes in coil inductance by means of constant current drive, and measuring voltage changes on a snubber. E.g. I wish to get X component directly, and thus have ferrous discrimination.

[daverave]

sounds very interesting if you can measure ferrous in this way !!! one of the best discrimination methods i saw somebody do some years ago was something called pivot point discrimination where each type of metal had its own pivot point so you could tell say a ring from a bottle top or whatever metal and each would have its own tone...and it worked !!!! but hard to impliment and the engineer didnt see the project through whi ch was a shame.