Heavy Duty Mosfet switching circuit..........
Started by unknown · · 19 posts · last reply 22 April 2013
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#1 ·
Could someone point me to a good opto-isolated mosfet switching circuit. I`m looking for something that will afford a little more protection than just switching a fet. I have seen in the past elaborate circuits with snubber diodes, caps,resistors,est. Maybe someone makes a prefab module ? I need to switch 200vdc at around 5 amps in the 40,000khz range. -
#2 ·
Bob Boyce's HD circuitry. -
#3 ·
I study everything Bob Boyce. I don`t know what you mean. -
#4 ·
Did you ever get a look at his heavy duty version?
His circuits all have external input ports.I cant remember the FET's he used for that one , the FETS I have are IRFPS3810, those were for one of his boards but I cant remember wich one....Ive been looking every where for any of his schematics past rev.c and cant find nutjing but express pcb files.Ive been busting my non electronics ass for over a month now trying to find a good simple variable frequency triangle wave ,negative ramp and sawtooth circuits but have consinstantly failed and am at witts end with just those simple frickin circuits.ANY help with a simple constant amplitude triangle wave and a negative ramp circuit will be much appreciated and I will most deffinately share the resulting circuitry and wave form I think alot of us will be interested in. -
#5 · date not recorded
i use igbt rated at 96 amps 600v i don~t remember the name now... and its not really important for you becasuse probably it won~t be available...
you must get the list of your local suplier to chose the better one or your tests, theres no one fits all solution but the greatest is the voltage and amps the better... -
#6 · date not recorded
I was looking for something opto-isolated to afford a little more protection for a freq. generator I cherish a lot. Maybe you could sketch something up for me ? -
#7 · date not recorded
Bobs boards are opto-isolated, the last version i had used the pcp116 opotos. -
#8 ·
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. -
#9 ·
they put out supply voltage with external inputs dont they? -
#10 ·
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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#11 · date not recorded
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. -
#12 ·
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.
attachment_12409 waveform.JPG
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#13 ·
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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#14 ·
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
PWM3fshc.pdf FQA8N100C.pdf auirgdc0250.pdf
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#15 ·
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. -
#16 ·
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. -
#17 ·
Sorry newguy, Link won`t work but you can find it on Hydrogen Garage site. I can provide a component list with corresponding locations on the board. Best I can do. Hope this helps. -
#18 ·
Thats cool Nick,ive got his schematics and stuff on an old computer but its been down for a while
but i do have em ill eventually figure some of my problems out ... rite now my biggest problem is figuring out why Im loosing 20 volts off transformer when i put the gate of the hexfet on it.
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#19 ·
hey Nick finally found what i needed to look at to help make my circuit a more robust circuit as Bobs ... it mayhelp you decide what all parts you may want to change to heavy duty your version ...
Here's a schematic of what all i have so far of the circuit im workin on:
attachment_12427 attachment_12429 post1.JPG post.JPG
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