It is part of the voltage divider that sets the gate DC voltage on the VFET and in turn controls the current flowing through it. But the 10k resistor only sets the minimum voltage and here you need quite a lot of volts on the gate. So, even 27k would be fine—it would just lower the adjustment range on the low end, which is most likely not needed.
The mosfet current source controls the current through the VFET. So the current is more or less constant. The VFET gate voltage, as part of Vgs, controls the drain-source on-resistance of the VFET, which sets the VFET drain voltage relative to the source voltage (Vds).
Since VFETs are quite variable from sample to sample, a trim pot in series with the R8 form a voltage divider, as mentioned by ra7, is used to supply an adjustable voltage to the VFET gate so that the design VFET Vds can be dialed in.
Since VFETs are quite variable from sample to sample, a trim pot in series with the R8 form a voltage divider, as mentioned by ra7, is used to supply an adjustable voltage to the VFET gate so that the design VFET Vds can be dialed in.
My problem too.Thanks guys as I've got a whole lot to learn, now if only I could find the time.
very good！谢谢大家，因为我有很多东西要学，现在只要我能找到时间。（我的意思是当我没有被妻子和女孩消耗时，我可以为自己争取的宝贵时间做的事情）
I bought from Mouser (I don’t have the VFET chassis, so not confirmed)
806-KPJX-PM-4S-S. (Power jack)
629-GRS-4021-0022. (Switch)
these have been mentioned in the threads somewhere. I looked them up on my orders
BTW, I confirmed that I did properly order one of the special VFET cases. I guess they are trickling out slowly, or shipping staged to different countries. I still have not heard about mine.
806-KPJX-PM-4S-S. (Power jack)
629-GRS-4021-0022. (Switch)
these have been mentioned in the threads somewhere. I looked them up on my orders
BTW, I confirmed that I did properly order one of the special VFET cases. I guess they are trickling out slowly, or shipping staged to different countries. I still have not heard about mine.
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My VFET special edition case did ship last night. I hope to get a lot done with that build next week (long weekend )
I have not installed the VFET and MosFet yet, wanting to fit the T bracket to the case before putting that all together. Not sure I will go as far as ZM did, but I will try to make it fit well. Well, and find my thermal grease tube.
)I have not installed the VFET and MosFet yet, wanting to fit the T bracket to the case before putting that all together. Not sure I will go as far as ZM did, but I will try to make it fit well. Well, and find my thermal grease tube.
Hi,
Can someone tell me if the TO-3 screws to mount the Sony P-Vfet and IRF250 will need to be conductivity isolated from the channel bracket when mounting these devices.
I see that only 8 nylon inserts are provided for the two channels in the round 3 output kit from the DIY store with the TO-3 and IRF250 4 thermal pads.
Please excuse me for my ignorance, but I presume that the outer TO-3 case for the Sony P-Vfet is uncoupled from the rest of the electrical circuit and sees no voltage.
Also, is it advisable to apply a non-conductive mica/thermal grease to both sides of the thermal pads when mounting the Vfet and IRF250?
TIA
Kind regards,
Benjisan
Yes, you need to use plastic bushing to isolate the screw because TO-3 body is collector. You may say VFET is uncoupled, but you will not afford to risk such precious VFET in case the bracket/HS/chassis accidentally connects to PS ground or negative.
The plastic bushings are for keeping the 2 leads (which go through the T bar to the circuit board), separate from the T Bar. There are 2 leads x 4 devices = 8 bushings.
As far as I can see, the "nut" end of the bolt/nut assembly grounds the "can" of the device to the circuit board. The device should be separated from the T Bar by the thermal pad.
Thermal pad - the silicone pad / Keratherm type pad don't need thermal grease. If you are using Mica sheet, or a ceramic thermal pad, then yes, non conductive grease on both sides.
As far as I can see, the "nut" end of the bolt/nut assembly grounds the "can" of the device to the circuit board. The device should be separated from the T Bar by the thermal pad.
Thermal pad - the silicone pad / Keratherm type pad don't need thermal grease. If you are using Mica sheet, or a ceramic thermal pad, then yes, non conductive grease on both sides.
So the poly tubes go in the bolt holes, not the ones where the VFET leads are. Man, I am glad this was brought up. The original VFET OS came pre-built, and I did not realize that those were to protect the bolt from the T-Bar. I have some ceramic pads. Does it matter if the nuts touch the solder pads on the circuit boards, or are those not connected to anything?
My VFET case arrives tomorrow, and I hope to construct the Part One P-Channel VFET amp this holiday weekend, with the boards you sent. I was planning to check the fitment of the T-Bar on the heatsinks before mounting the circuit board, and VFet/Mosfet, to the T-Bar.
I also want to dry fit the TUBA and Bulwark cards in the case to avoid impingement issues.
My VFET case arrives tomorrow, and I hope to construct the Part One P-Channel VFET amp this holiday weekend, with the boards you sent. I was planning to check the fitment of the T-Bar on the heatsinks before mounting the circuit board, and VFet/Mosfet, to the T-Bar.
I also want to dry fit the TUBA and Bulwark cards in the case to avoid impingement issues.