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Winfield Hill
Guest
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 Posted:
Tue Feb 08, 2005 7:33 pm Post subject:
Re: Digital dimmer: Triac vs MOSFET in a circuit? |
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Jim Thompson wrote...
| Quote: |
Win, Did you ever get anywhere with comparing the MOSFET models?
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Thanks for the reminder.
--
Thanks,
- Win
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Winfield Hill
Guest
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| Posted:
Tue Feb 08, 2005 8:45 pm Post subject:
Re: Digital dimmer: Triac vs MOSFET in a circuit? |
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Andrew Gabriel wrote...
| Quote: |
Winfield Hill writes:
Andrew Gabriel wrote...
Winfield Hill wrote...
What kind of FET did you use?
Don't seem to be able to locate my design notes at the moment, but
looking back at my purchase orders for 1998 when I designed and
built this, it looks like I choose Motorola MTW24N40E TMOS power
FETs (400V, 24A). (ISTR the problem choosing a high voltage/current
MOSFET was finding one that anyone stocked and would supply in
small numbers.)
Pretty good. With a 160m-ohm Rdss(on), at 10A that would only be
16W dissipation.
You have to add the forward voltage drop of the integral reverse
polarity bypass diode too, which probably takes it nearer 25W
total, but it was easily dissipated with only a small fan running
silently at low speed.
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I assume you used the standard back-to-back series connection with
both sources tied together and both gates tied together. In this
preferred configuration, both FETs are on, with one conducting
"backwards" shorting out its source-drain diode, and you end up
with twice the power dissipation of a single FET. Of course, if
the voltage drop across the FET rises to more than the diode drop,
as in your case (see below), then these mechanisms work together
sharing the load current.
| Quote: | What was your peak load current for 1kW average
power?
I'd have to work it out... Actual rating of the pan was
1050W @ 120V = 13.7 ohm. ISTR the phase angle at cutoff was 43º
(a bastard to work out;-). 240VAC * sqrt(2) = 339V peak
339 * sin(43º) = 231V at cutoff. 231 / 13.7 = 16.9A
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OK, 17A^2 * 0.16 ohms = 46 watts peak for the forward FET. It's
a bit painful to calculate the RMS power, say about 15-20 watts.
The reverse FET, with its diode helping, would be a little lower.
| Quote: | Did you consider IGBTs instead?
No, mainly because they weren't around when I learned electronics
so I don't know much about their characteristics or have any real
life experience using them.
I'll find a good one for comparison.
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The reason IGBTs are attractive for applications like this is that
for a smaller part with similar or less silicon area to a FET, it
enjoys a smaller voltage drop at high currents. Your MTW24N40E FET
drops up to 2.7V at 17A, which a smaller IGBT can easily beat. For
example, a TO-220 600V 12A Fairchild HGTP12N60C3D IGBT drops 1.7V
at 17A. And Fairchild's HGTG30N60B3D, a 30A IGBT with a slightly
smaller die size than your big FET (rated at 208W compared to the
FET's 250W), drops only about 1.0 volt. That's a big improvement.
http://www.fairchildsemi.com/pf/HG/HGTP12N60C3D.html
http://www.fairchildsemi.com/pf/HG/HGTG30N60B3.html
--
Thanks,
- Win |
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ArdentGuy
Guest
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| Posted:
Thu Feb 24, 2005 9:05 pm Post subject:
Re: Digital dimmer: Triac vs MOSFET in a circuit? |
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Hi,
In response to "Do you have a dimmer circuit with MOSFET to suggest?"
Tomi responded with "CMOS gate implement
s reverse phase control - this circuit implements a
"reverse" phase control, using only a single CMOS 4001 quad NOR gate,
conduction begins at the zero crossing of the ac sine wave and the
turn-off timing is adjusted based on dimmer setting
http://www.e-insite.net/ednmag/archives/1998/052198/11DI.htm#CMOS%20gate%20implements"
I'm interested! I can get to the article but the circuit diagram (figure
1) is supposedly stored in a .PDF file...that will not come up. Has
anybody got another source for this circuit? Or is it just me who can't
get to the .PDF file?
Thanks,
John
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Tomi Holger Engdahl
Guest
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| Posted:
Fri Feb 25, 2005 4:23 pm Post subject:
Re: Digital dimmer: Triac vs MOSFET in a circuit? |
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"ArdentGuy" <jts@att.net> writes:
| Quote: | Hi,
In response to "Do you have a dimmer circuit with MOSFET to suggest?"
Tomi responded with "CMOS gate implement
s reverse phase control - this circuit implements a
"reverse" phase control, using only a single CMOS 4001 quad NOR gate,
conduction begins at the zero crossing of the ac sine wave and the
turn-off timing is adjusted based on dimmer setting
http://www.e-insite.net/ednmag/archives/1998/052198/11DI.htm#CMOS%20gate%20implements"
I'm interested! I can get to the article but the circuit diagram (figure
1) is supposedly stored in a .PDF file...that will not come up. Has
anybody got another source for this circuit? Or is it just me who can't
get to the .PDF file?
|
Downloading the PDF did not work for me either :-(
I has link to this ciruit, and posted the address whe I saw that
circuit page to work... Did not test the download of all parts..
EDN magazine seems to change their archive every now and them...
Result beuing that links tend to break down every now and them.
It is now not the particular link on the t circuit, every PDF
link on that page seems to be broken because of their new system..
One idea would be to contact the webmaster of that site
to report of the problem and ask to correct it.
I might have that circuit printed on paper somewhere, maybe
even electronic copy...
--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/ |
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ArdentGuy
Guest
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| Posted:
Mon Feb 28, 2005 6:16 pm Post subject:
Re: Digital dimmer: Triac vs MOSFET in a circuit? |
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Tom,
Yep....every single link on the page seems to be busted. I sent an e-mail
to the webmaster right after I posted here four days ago. I haven't
gotten a response yet....but then again, it's Monday morning!
If you can reproduce the circuit, that would be a great help!
Thanks,
John |
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