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Burnit

Wed Nov 12 2008, 12:42AM

Registered Member #1801 Joined: Fri Nov 07 2008, 01:51AM
Location:
Posts: 5

Hi All,

New to the Forum & a novice at electronics & just learning, i have been playing around with some coil driver circuits, 555timer, IRFP450A Mosfets etc, 12v Dc power source..

I need to change the output signal of the driver to a Sine wave.

I have found the "Circuit 1" Attachment on the Net, my driver naturally has a + & - output terminals which i assume connect to the + & - as shown on the Schematic.
On the Mosfets in the schematic i have marked 1 & 2, where do these pins connect to??

In Attachment "Circuit 2", where do i connect the output from my driver, it shows a 320v connection & an earth connection & then the same pins on the Mosfets as above?

Thanks

Arcstarter

Wed Nov 12 2008, 03:20AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Well, on the first schematic, the + and - is actually the input (from power supply) and the two other pins on the mosfet are the 'gates' Which when you send a pulse through it, it turns the mosfet on(to where it conducts).

On the second schematic, the 320 volts is your positive dc input, and the earth is your common ground, or negative. The output is in between the two mosfets and in between the two capacitors. It is called a halfbridge. The mosfets gate will have to be driven with what is called a 'gate drive transformer' also known as gdt. The reason for that is because you want one mosfet to turn on while the other is off, and then when the first one turns off you want the other one on. The gdt is an easy approach to get the mosfets to turn on oppositely. You could just drive number one with a non-inverting driver(ucc37322) and mosfet two with an inverting driver(ucc37321), but the gdt gives extra protection.

You are just going to have to read up on this stuff until you get it, which could take years. It took me about a year or two to understand what i just told you.

Oh, and before i said any of that i should have first said, the output from a 555 is a squarewave, and the mosfets will not turn it into a sinewave. I don't know how to turn a 555 output into a sinewave or even if you can(i am sure there is something crazy out there that you can do).

So basically, just read up on it for many years before trying it.

rp181

Wed Nov 12 2008, 03:30AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
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those circuits take alternating inputs into the gate, creating AC power. It is not however a sine wave.

uzzors2k

Wed Nov 12 2008, 09:00PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

What do you need the sine wave for? Those two circuits will actually turn a square wave into a sine wave at the tank circuit, how practical it is is another question. (Where'd you get mine from btw, it's missing some text?) What Arcstarter told you is true, these are not complete circuits by any means. They just illustrate the principle of resonant induction heater circuits.

Arcstarter

Wed Nov 12 2008, 09:19PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Uzzors wrote ...

What do you need the sine wave for? Those two circuits will actually turn a square wave into a sine wave at the tank circuit, how practical it is is another question. (Where'd you get mine from btw, it's missing some text?) What Arcstarter told you is true, these are not complete circuits by any means. They just illustrate the principle of resonant induction heater circuits.

Yea, it is more of the power section, that requires some sort of driver, whether it is simple 555 or a more sophisticated driver. The driver hence the name 'driver' just sends the pulse to the mosfets to drive them. You could actually make a flyback driver, with higher frequency(you would have to tweak it) that uses the 555 and make a gate driver like a ucc37322 and ucc37321 and a gate drive transformer and feed that into the halfbridge. Use steve wards simple schematic:

You can just change c1(the 2n capacitor) until you get the frequency you need.

Burnit

Mon Nov 17 2008, 10:13PM

Registered Member #1801 Joined: Fri Nov 07 2008, 01:51AM
Location:
Posts: 5

Thanks Arcstarter & everybody for the advise.

Uzzors: Not sure what schematic is yours, both were suggested by someone else?

I have just had a look at your site & your Induction Heater project & i now noticed the same schematic.

While on the induction heater, how much heat can be applied to a 30-40mm diameter x 75-100mm long round solid section of steel at 120watts & 240 Watts if the steel section was insulated from the ambient temperature.

Would you get it to glow dull or bright red at 120 Watts or 240W, looks like a good project, can i get some assistance if i give it a go?

I need to heat some small pices of steel mentioned aboved & have been using an oxy torch for years, this looks like a great little project.

Dago

Mon Nov 17 2008, 10:53PM

Registered Member #538 Joined: Sun Feb 18 2007, 08:33PM
Location: Finland
Posts: 181

Burnit wrote ...

While on the induction heater, how much heat can be applied to a 30-40mm diameter x 75-100mm long round solid section of steel at 120watts & 240 Watts if the steel section was insulated from the ambient temperature.

If it was ideally insulated from ambient temperature it would reach infinite temperature, the power would only affect the speed of the heating. Practically it is harder to say.

uzzors2k

Tue Nov 18 2008, 04:03PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Bingo. It's just a matter of physics, in fact I think high school physics are enough to determine the equilibrium temperature at a given input power. I'll look into it. Getting metal to glow dull red can be done with many different kinds of induction heater circuits. Look up ZVS induction heaters for the simplest kind. Even a 555 driver is sufficient.

Burnit

Tue Nov 18 2008, 09:53PM

Registered Member #1801 Joined: Fri Nov 07 2008, 01:51AM
Location:
Posts: 5

I just knocked up the circuit suggested from Penguin's lab, he has a 390pf cap in the circuit, what type of caps are used for this?
Does this circuit require a transformer etc or does it drive the work coil directly from the circuit??

uzzors2k

Wed Nov 19 2008, 11:17AM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

The 390pF cap is part of the 555 timing components. I don't think he's using a resonant tank circuit, just the spool of wire shown as a work coil. Just wind something similar and change the 555 timing components to get a range of 200 to 400 kHz.

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