Threshold Pot doesn't work

[waltr]

Ok, good going.

[h9361]

Damping resistor power dissipation will double if you double the pulse rate.

Design a better audio driver. For example, you could use an LM386.

Hello
Dear Carl.
Can you suggest me some MOSFETs for Q3 (IRF740) which can be able to tolerate higher temperature?

[Carl-NC]

If you use a MOSFET with a higher breakdown voltage (600V, 800V, etc) it will not get as hot.

[h9361]

If you use a MOSFET with a higher breakdown voltage (600V, 800V, etc) it will not get as hot.

thanks.
Do you think the K2611/2SK2611 (900V, 9A) works in HHD?

[h9361]

Or the FQA11N90 ?
It's fast swithcing, 900V-11.4A

http://www.farnell.com/datasheets/17022.pdf

[kt315]

MOSFET with a higher breakdown voltage has more Rds. that's rule.

[Altra]

How about a heat sink?

[h9361]

Thank you all for your help.
Unfortunately, heat sink gets very hot because i'm using high pulse with for my HHD+GB.
I checked RDs of FQA11N90, it's like IRF840. I already used IRF840, it worked.
Do you think it works if i use on my HHd?
Thanks.
http://www.farnell.com/datasheets/17022.pdf

[Altra]

Try a larger heat sink. The FQA11N90 uses a T0-3P case which is larger than a IRF740 (T0-220 case). It may not fit your PCB.

[Carl-NC]

I have found that the performance of MOSFET switches is difficult to gauge by the data sheet, you have to buy & try.

There are 2 mechanisms that create power in the switch. First is the turn-on time, for that you want low RDS, especially if you are using a wide pulse width. Second is the flyback region if the MOSFET breaks down so to avoid that you want a high BVDSS. In most PI designs the avalanche is the biggest heat generator which is why I said to get a higher breakdown. But you should also pay attention to RDS, it's pretty easy to calculate what that power will be. Remember to include the coil resistance.

[h9361]

I have found that the performance of MOSFET switches is difficult to gauge by the data sheet, you have to buy & try.

There are 2 mechanisms that create power in the switch. First is the turn-on time, for that you want low RDS, especially if you are using a wide pulse width. Second is the flyback region if the MOSFET breaks down so to avoid that you want a high BVDSS. In most PI designs the avalanche is the biggest heat generator which is why I said to get a higher breakdown. But you should also pay attention to RDS, it's pretty easy to calculate what that power will be. Remember to include the coil resistance.

Hello
Dear Carl.
Yesterday, i received the MOSFET and tested over my HHD.
It works but has a problem. Since its current is high, i can not set frequency of my machine to 1KHz because my BAT LED will turn up.
So, i have to decrease frequency near to 850Hz. I prefer to obey Mr. Altra's advice, using larger heat sink for IRF740/840.

As you know, i added GB to my HHD and set its delay to 8us. I built a coil that is able to work at the delay (Teflon-AWG22-silver, it's wire of TDI Coil), i didn't used any spacer. The Coil works vey nice at the delay in a fixed state without movement so that its sensitivity is vey excellent (My TP4 form is clear). For shielding (Faraday Shielding ), i used a vey very thin copper foil, but i have a problem. Unfortunately, my machine will have action as soon as moving coil (left/right or up/down). This is only at the low delay, not at high delay.

Do you think this is because of changing coil capacitance? Do you have any suggestion for eliminating this effect?
I think i should use a thicker foil. Some people told me i must use only Graphite Spray!
Do you have any suggestion?
Thanks.

[MartinB]

Hello
Dear Carl.
Yesterday, i received the MOSFET and tested over my HHD.
It works but has a problem. Since its current is high, i can not set frequency of my machine to 1KHz because my BAT LED will turn up.
So, i have to decrease frequency near to 850Hz. I prefer to obey Mr. Altra's advice, using larger heat sink for IRF740/840.

As you know, i added GB to my HHD and set its delay to 8us. I built a coil that is able to work at the delay (Teflon-AWG22-silver, it's wire of TDI Coil), i didn't used any spacer. The Coil works vey nice at the delay in a fixed state without movement so that its sensitivity is vey excellent (My TP4 form is clear). For shielding (Faraday Shielding ), i used a vey very thin copper foil, but i have a problem. Unfortunately, my machine will have action as soon as moving coil (left/right or up/down). This is only at the low delay, not at high delay.

Do you think this is because of changing coil capacitance? Do you have any suggestion for eliminating this effect?
I think i should use a thicker foil. Some people told me i must use only Graphite Spray!
Do you have any suggestion?
Thanks.

Have you tried Scotch 24 mesh. This gives a lower capacitance than copper foil.

[h9361]

Have you tried Scotch 24 mesh. This gives a lower capacitance than copper foil.

Unfortunately, it is not at my country.

[Carl-NC]

Does you get falsing when moving the coil in air, or only close to the ground?
Is the coil is a rigid housing or embedded in epoxy?

[h9361]

Does you get falsing when moving the coil in air, or only close to the ground?
Is the coil is a rigid housing or embedded in epoxy?

I tested with/without epoxy, both of them has the problem.
In Air and close ground has false signal.