IRFP250 MOSFET circuit design help.

[gary350]

I am teaching myself about MOSFET. We called these FET when I was in college.

It looks like I have to design my own Induction heater circuit if I want one that really works.

I have 3 questions.

If I use 120 VAC as my supply voltage X 1.414 = 169 VDC.

How can I limit the current to 5.91 amps to make a 1000 watt induction heater?

How do I build an RF osc to switch the transistor on/off at 200KHz I don't think a 555 timer will operate above 20K?

What about the 45 uh coil? If 6 turns is 1.5 uh then 4 turns is 1 uh and 180 turns is 45 uh.

**broken link removed**

 

[ronv]

They are beasts to build, but here is a pretty good write up.

https://www.richieburnett.co.uk/indheat.html

 

[shortbus=]

@gary350 Someone will correct me if wrong, but in your circuit, when the mosfet is "turned on" it will short circuit the supply! The mosfet should be between the inductor and ground/0V to make it switch at your frequency.

 

[gary350]

@gary350 Someone will correct me if wrong, but in your circuit, when the mosfet is "turned on" it will short circuit the supply! The mosfet should be between the inductor and ground/0V to make it switch at your frequency.

Your right I made a mistake. Ok..... I uploaded a different circuit drawing above.

I wonder if current limiting can be done like this. Connect 2 microwave oven transformers MOT connected together. These are shunt transformers so a 1000 watt transformer will not pull more than 1000 watts even with the output is short circuited. Connect both High Voltage windings together, Input will be 120 VAC and output will be 120 VAC limited to 1000 watts. After the Bridge Rectifier and Filter Capacitor output will be 169.68 VDC at 1000 watts. Only problem with this is the transformers will over heat after several minutes and 2 transformers are very heavy so it won't be very portable.

**broken link removed**

 

[Ubergeek63]

try a https://www.electro-tech-online.com/custompdfs/2012/02/UC3842B.pdf

 

[gary350]

They are beasts to build, but here is a pretty good write up.

https://www.richieburnett.co.uk/indheat.html

Some of that information is not clear to me.

It does not tell how to build the 45 uf matching inductor.

It does not tell how to turn the MOSFET on/off at 200KHz.

It does not tell how to build the work coil. The picture shows 6 turns but no diameter and no length.

 

[ronv]

You can use this calculator to get the inductors.
I think I would use a good Driver like:
https://www.electro-tech-online.com/custompdfs/2012/02/ir2110.pdf
I think I would use a couple of inverters with some delay in between to make sure both FETs are not on at the same time. These you could drive with an adjustable 555 so you could find the resonant peak.
Be careful!

 

[gary350]

You can use this calculator to get the inductors.
I think I would use a good Driver like:
https://www.electro-tech-online.com/custompdfs/2012/02/ir2110.pdf
I think I would use a couple of inverters with some delay in between to make sure both FETs are not on at the same time. These you could drive with an adjustable 555 so you could find the resonant peak.
Be careful!

I don't understand this pdf link. It looks like a driver for the mosfets but what about the work coil, choke coil, current limiting capacitor, and frequency capacitors?

 

[ronv]

Ahh, the missing link.

https://www.daycounter.com/Calculators/Air-Core-Inductor-Calculator.phtml

Let me read the example link again.

 

[ronv]

I think I would try this one attached.

Use this type cap. We will need to model it to see how many of what size to make the parallel resonant one as the current is very high in them.
https://www.electro-tech-online.com/custompdfs/2012/02/940C.pdf

 

[gary350]

I think I would try this one attached.

Use this type cap. We will need to model it to see how many of what size to make the parallel resonant one as the current is very high in them.
https://www.electro-tech-online.com/custompdfs/2012/02/940C.pdf

I don't think that circuit works. If both MOSFETs are ON at the same time it is a short circuit across the power supply. If both MOSFETs go ON/OFF 180 degrees apart the MOSFET on top supplies power to the work coil same thing as my circuit but when the MOSFET on the bottom comes ON it is a short circuits across the work coil and NO power flows because the TOP MOSFET is NOT ON. Without the bottom MOSFET the circuit is identical to mine. Maybe I am missing something maybe the bottom MOSFET to act like points on an ignition coil.

 

[shortbus=]

Gary350 - Others have linked to this page before, but you are going to have to read and understand for yourself what it is saying https://www.richieburnett.co.uk/indheat.html All of the answers are in there, but the answers are formed by more questions, that more research will answer. I don't think you will find an easy solution, this is done on purpose, to protect both you and the author of the page.

Have you seen these links? https://www.neon-john.net/Induction/heater.htm

https://www.electro-tech-online.com/custompdfs/2012/02/schematic.pdf

https://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=40&t=1600

 

[gary350]

MOSFET is smaller than a dime in a T0-247 case, what size heat sink does it need. I don't see how this tiny thing can handle 1000 watts.

https://www.ebay.com/itm/260816297754?_trksid=p5197.c0.m619

 

[shortbus=]

Here is the best write-up on understanding mosfet ratings I've found - http://mcmanis.com/chuck/robotics/projects/esc2/FET-power.html

 

[shortbus=]

Some more links with schematics for you-

http://www.rmcybernetics.com/projects/DIY_Devices/diy-induction-heater.htm

http://www.mindchallenger.com/inductionheater/

**broken link removed**

http://www.neon-john.net/Induction/Roy/Roy.htm

 

[ronv]

I don't think that circuit works. If both MOSFETs are ON at the same time it is a short circuit across the power supply. If both MOSFETs go ON/OFF 180 degrees apart the MOSFET on top supplies power to the work coil same thing as my circuit but when the MOSFET on the bottom comes ON it is a short circuits across the work coil and NO power flows because the TOP MOSFET is NOT ON. Without the bottom MOSFET the circuit is identical to mine. Maybe I am missing something maybe the bottom MOSFET to act like points on an ignition coil.

You need the bottom MOSFET so you have a path to ground on the oposite half cycle.
Use 12 of these caps in parallel for the resonant circuit.
https://www.mouser.com/ProductDetail/Cornell-Dubilier/940C30S47K-F/?qs=gSIQ2CbtXsYGKLy6248XRQ==
Make the matching inductor 50Uh.
You can use a single .47 Ufd of the same type for the second cap.
Try out the calculator for the inductors and let us know what you come up with.

The system is a few hundred watts the fets are a very small part of that power loss.

 

[gary350]

You need the bottom MOSFET so you have a path to ground on the oposite half cycle.
Use 12 of these caps in parallel for the resonant circuit.
https://www.mouser.com/ProductDetail/Cornell-Dubilier/940C30S47K-F/?qs=gSIQ2CbtXsYGKLy6248XRQ==
Make the matching inductor 50Uh.
You can use a single .47 Ufd of the same type for the second cap.
Try out the calculator for the inductors and let us know what you come up with.

The system is a few hundred watts the fets are a very small part of that power loss.

What about the driver circuit. I assume V2 and V3 are the 2 drivers and probably 180 degrees out of phase with each other.

 

[ronv]

Yes, you can use the driver in the link, your FET, and a 555 with adjustment for the signal.

 

[gary350]

What is the best way to make the 50 uh coil?

Online inductor calculator says.

Inductance 0.05 mH
DC Resistance 0.04 Ohms
Wire Gauge 14 AWG
Wire Diameter 64.1 mils (1 mil = .001 in)
Coil Length 1 in
Coil Inner Diameter 1 in
Coil Outer Diameter 1.51 in
Average Turn Diameter 1.14 in
Wire Length 14.92 feet

or

Inductance 0.05 mH
DC Resistance 0.09 Ohms
Wire Gauge 18 AWG
Wire Diameter 40.3 mils (1 mil = .001 in)
Coil Length 1 in
Coil Inner Diameter 1 in
Coil Outer Diameter 1.24 in
Average Turn Diameter 1.05 in
Wire Length 14.51 feet
Copper Weight 0.07 pounds
Turns 53
Levels 2.14
Turns/Level 24.81

or

Inductance 0.05 mH
DC Resistance 0.15 Ohms
Wire Gauge 20 AWG
Wire Diameter 32 mils (1 mil = .001 in)
Coil Length 1 in
Coil Inner Diameter 1 in
Coil Outer Diameter 1.13 in
Average Turn Diameter 1.03 in
Wire Length 14.51 feet
Copper Weight 0.04 pounds
Turns 54
Levels 1.73
Turns/Level 31.25

or

Inductance 0.05 mH
DC Resistance 0.38 Ohms
Wire Gauge 24 AWG
Wire Diameter 20.1 mils (1 mil = .001 in)
Coil Length 1 in
Coil Inner Diameter 1 in
Coil Outer Diameter 1.08 in
Average Turn Diameter 1 in
Wire Length 14.44 feet
Copper Weight 0.02 pounds
Turns 55
Levels 1.11
Turns/Level 49.75


I have 40 lbs of #20 wire and 200 lbs of #24 enamel coated copper wire. I have some misc pieces about 4 ft of #14 and 12 ft of #18 but I can buy anything I needed.

 

[ronv]

The 20 awg should handle the current. The 24 is a little small.