Author Topic: Heavy Duty Mosfet switching circuit..........  (Read 7501 times)

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Re: Heavy Duty Mosfet switching circuit..........
« Reply #8 on: April 13, 2013, 05:44:17 am »
they put out supply voltage with external inputs dont they?

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Re: Heavy Duty Mosfet switching circuit..........
« Reply #9 on: April 14, 2013, 10:27:20 am »
Yes Bob`s boards are opto-isolated. I have them all but the hex controller. Problem is they output about 12vdc. I want to pulse 200+ vdc, 5amps at around 42,000khz.

Dear Nick,

I think i can help here with your 12v output issue.
In stead of hooking the end fets up to the 12v powersupply, you can choose to hook them up to another powersupply with higher voltage range. Make sure that your fets can handle the higher voltage and that the negatives of all powersupplys are connected with each other.

If you have a drawing of your current setup, then please mail or post it here, so i can make adjustments to it, if you like.

Best regards
Steve

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Re: Heavy Duty Mosfet switching circuit..........
« Reply #10 on: April 14, 2013, 23:23:40 pm »
Steve , I actually thought about this and wondered if it could work. It is a Boyce G board I want to use. This board is able to reach a wide range of freq. and duty cycles. The  IRP540Z fets switch fast and sharp. It is already optoisolated. Its only downfall is a duty cycle over 35 - 40 % on time will heat up the fets and burn them up. No schematics are available for the G board, but a detail view of the board itself, top and bottom can be viewed at the Hydrogen Garage site. You might swap out the fets and isolate the input from the rest of the board but that might be beyond what I know how to do.

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Re: Heavy Duty Mosfet switching circuit..........
« Reply #11 on: April 15, 2013, 05:49:08 am »
Im getting closer to what i want to do finally....  this signal is comeing out of a 555 into a small audio transformer and into a MOSFET  and this waveform is the result of that... now i have to get that into an AC waveform...I cant believe how perfect this part of the waveform is after sveral weeks of tinkering :) My major problem is getting an undistorted AC current waveform of this type :/ may take me years.....i thinl wat i may try to do is get the down slope to oscillate...notsure yet.
« Last Edit: April 15, 2013, 19:10:02 pm by newguy »

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Re: Heavy Duty Mosfet switching circuit..........
« Reply #12 on: April 16, 2013, 01:02:16 am »
Im getting closer to what i want to do finally....  this signal is comeing out of a 555 into a small audio transformer and into a MOSFET  and this waveform is the result of that... now i have to get that into an AC waveform...I cant believe how perfect this part of the waveform is after sveral weeks of tinkering :) My major problem is getting an undistorted AC current waveform of this type :/ may take me years.....i thinl wat i may try to do is get the down slope to oscillate...notsure yet.

Have you ever tried a transformer with two input coils?

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Re: Heavy Duty Mosfet switching circuit..........
« Reply #13 on: April 16, 2013, 01:32:06 am »
Steve , I actually thought about this and wondered if it could work. It is a Boyce G board I want to use. This board is able to reach a wide range of freq. and duty cycles. The  IRP540Z fets switch fast and sharp. It is already optoisolated. Its only downfall is a duty cycle over 35 - 40 % on time will heat up the fets and burn them up. No schematics are available for the G board, but a detail view of the board itself, top and bottom can be viewed at the Hydrogen Garage site. You might swap out the fets and isolate the input from the rest of the board but that might be beyond what I know how to do.

Hi Nickranger,

I had a look for you on the Boyce schematics.

Please read what the current wire description is:

TB2 has 3 connections as follows;

Output 1 is connected to the cold side of primary 1.
Output 2 is connected to the cold side of primary 2.
Output 3 is connected to the cold side of primary 3.

The hot sides of primaries 1, 2, and 3 are brought together, and connected to
the 13.8 VDC power supply positive connection via heavy guage wire, through a 20 Amp fuse or DC circuit breaker, the contacts of a heavy duty (20 Amp or more rated) power switching relay, and a heavy duty choke.

------------------------------------
My comments:
If you use the IRF540Z mosfets, then you can go up to max 100V.
A 1000V with same specs for amps like the irf540, is difficult. Options are possible within the IRF range mosfets, like the IRF840 (500V by 8 amps)
or the FQA8N100C which does 1000V by 8 amps.
All can be put into your BB board.

Now, in stead of connecting the hot sides of primaries 1,2,3 to the 13,8v powersupply, you hook them up to the 1000V powersupply. Just make sure that the negative of that 1000V powersupply is also connected to J3 pin 1.

Thats all.

Steve

http://hydrogengarage.com/pwm3g/pwm3g.htm






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Re: Heavy Duty Mosfet switching circuit..........
« Reply #14 on: April 17, 2013, 02:35:32 am »
Hey Nick, could you draw up one channle of his G board and post a pik of it?  I need so much help with making my 555 circuit a proper circuit its pitiful.

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Re: Heavy Duty Mosfet switching circuit..........
« Reply #15 on: April 17, 2013, 03:38:30 am »
Newguy, Love to help you out, but drawing up a channel is slightly over my head. Thats why I`m asking for help. If you can follow it there is very good pics of the G board front and back here: http://stores.homestead.com/hydrogengarage/-strse-31/PWM3f%2C-pulsed-width-modifier%2C/Detail.bok       I can provide a component list with corresponding  placement on the board if that will help. Best I can do.