Potentiometer for critical damping tool

[Qiaozhi]

Qiaozhi has wrong.
Min resistance is 181 not 118 Ohms

Sorry guys, that was a typo. Of course, Geo is correct. See ITMD Edition 2 - page 155.

[homefire]

As we are only Damping the Coil Circuit not Sinking a load you really do not need a high watt pot. The total Current going to and returning from the coil is not transversing the test set up. The Two Watt Pot I'm using seems to be working just fine. The majority of power is just going to Ground via the coils main circuit path. Without doing the math I'm sure the 2w 750volt Pot won't do the Chernobyl thing.

[Altra]

...i just use a resistor and a mosfet. 100 ohm resistor on drain of nmosfet and then vary voltage on gate. Resistor value will depend on type of mosfet. Works with p or n mosfets and later you can control it using cpu.
Pots are too noisy / expensive / etc.

How do you handle the mosfet's intrinsic diode? I've wanted to try this for awhile, after reading Nelson's patent.

[moodz]

.. basically if you are have a positive flyback with the Resistor on the drain of a N mosfet then the body diode wont conduct unless the flyback swings negative ..
.... for negative flyback use a P type mosfet.

[Altra]

Okay for the high voltage flyback. But what about the low voltage energizing pulse, won't the current bypass the mosfet through the diode? During on time you would have a 100ohm in series with a forward biased diode that parallels the coil. This is why some preamp gating schemes use two fets in series the first blocks the high voltage and second the energizing pulse. Maybe I am looking at it wrong.

Thanks