I'm wondering what people are doing to use IGBTs for AC line switching
(phase control, reverse phase control, and PWM for sine wave chopping). I
see a couple ways of doing it, but have not seen any ap notes on it (maybe
a list member can direct me to some). One method would be to use a single
IGBT with a diode bridge. Another would be to use a pair of IGBTs with
steering diodes. Then there's the issue of driving the gates of the IGBTs.
I'm used to triac drive using an MOC3020 or similar. The MOC pulls the
gate towards MT2 to fire the triac. Once fired, the voltage across the
triac is 1.5V or so. It doesn't seem that a similar gate drive scheme
could be used with an IGBT (pulling the gate to the collector) without
getting a relatively high voltage across the IGBT due to the gate
threshhold voltage. It seems the alternatives are the use of a separate
floating gate drive power supply or a pulse transformer to drive the gate.
What is typically being used?
One clever thing he suggests that is safest and cheapest (<$8.00USD) is
to use an in-line cadmium sulfide controlled AC light controller.
(a.k.a. "Twilight" light socket). The Radio Shack part number is
apparently defunct, but an image of it still exists on the RS website here:
I tried bring up how to do PWM for sine wave chopping a few months ago
(AKA PWM AC phase control). But certain people on the list server seen
it as their duty to promote SMPS topologies as the absolute only way to
do it (the thread went downhill from there), instead of actually
discussing how to make a circuit that could modify the magnitude of a
50/60hz AC pure sine wave with either a Mosfet or IGBT (i.e., sine wave
into circuit, sine wave out at lower RMS voltage). I ran into the same
technical problem you apparently have. I'd be happy to discuss that
particular design option with you (preferably offlist).
>I'm wondering what people are doing to use IGBTs for AC line switching
>(phase control, reverse phase control, and PWM for sine wave chopping). I
>see a couple ways of doing it, but have not seen any ap notes on it (maybe
>a list member can direct me to some). One method would be to use a single
>IGBT with a diode bridge. Another would be to use a pair of IGBTs with
>steering diodes. Then there's the issue of driving the gates of the IGBTs.
>I'm used to triac drive using an MOC3020 or similar. The MOC pulls the
>gate towards MT2 to fire the triac. Once fired, the voltage across the
>triac is 1.5V or so. It doesn't seem that a similar gate drive scheme
>could be used with an IGBT (pulling the gate to the collector) without
>getting a relatively high voltage across the IGBT due to the gate
>threshhold voltage. It seems the alternatives are the use of a separate
>floating gate drive power supply or a pulse transformer to drive the gate.
>What is typically being used?
>
>THANKS!
>
>Harold
>
>
>
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>-----Original Message-----
>From: spam_OUTpiclist-bouncesTakeThisOuTmit.edu [.....piclist-bouncesKILLspam@spam@mit.edu]
>Sent: 28 June 2005 18:11
>To: Microcontroller discussion list - Public.
>Subject: Re: [EE] IGBT for AC line switching?
>
>
>Hi Harold,
>
>I tried bring up how to do PWM for sine wave chopping a few months ago
>(AKA PWM AC phase control).
Out of interest, how does PWM relate to 'phase control' which AFAIK is what dimmer switches use? I'm (probably naively) thinking that sine wave chopping is simply turning on and off an AC current with a PWM driven switch. Does it have to be locked to the phase of the AC supply?
Regards
Mike
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At 11:10 AM 6/28/2005, Bob S. wrote:
>Hi Harold,
>
>I tried bring up how to do PWM for sine wave chopping a few months ago
>(AKA PWM AC phase control). But certain people on the list server seen it
>as their duty to promote SMPS topologies as the absolute only way to do it
>(the thread went downhill from there), instead of actually discussing how
>to make a circuit that could modify the magnitude of a 50/60hz AC pure
>sine wave with either a Mosfet or IGBT (i.e., sine wave into circuit, sine
>wave out at lower RMS voltage). I ran into the same technical problem you
>apparently have. I'd be happy to discuss that particular design option
>with you (preferably offlist).
>
>Harold Hallikainen wrote:
>
>>I'm wondering what people are doing to use IGBTs for AC line switching
>>(phase control, reverse phase control, and PWM for sine wave chopping).
<snip>
Why not keep it on-list? Yeah - there is added noise but hidden in some
that noise might - just might - be something worth exploring.
And *if* the topic starts to head off in the wrong direction, ignore those
messages and steer the topic back to where it should be.
Celebrating 21 years of Engineering Innovation (1984 - 2005)
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For the light dimmer I made I detected the zero cross point to start my
timing then turned a traic on after x amount of time to give the
required amount of brightness.
So yes this was PWM in sync with the mains and I would also say it is
phase control but not in the sense of altering the incoming phase of the
mains to some other phase angle or frequency.
_______________________________________
Roy
Tauranga
New Zealand
_______________________________________
> >I tried bring up how to do PWM for sine wave chopping a few months ago
> >(AKA PWM AC phase control).
>
>Out of interest, how does PWM relate to 'phase control' which AFAIK is
>what dimmer switches use? I'm (probably naively) thinking that sine wave
>chopping is simply turning on and off an AC current with a PWM driven
>switch. Does it have to be locked to the phase of the AC supply?
Ignore that the power supply is a sine wave. Now apply high frequency PWM
to the input, then filter out the PWM components. The output is a smaller
version of the input.
If the PWM frequency is high enough, the fact that the input is a sine wave
doesn't matter. The net result is that the output can be varied by
changing the PWM duty cycle - even though the output is still a mains
frequency sine wave.
Celebrating 21 years of Engineering Innovation (1984 - 2005)
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piclist-bounces@mit.edu wrote:
>> I tried bring up how to do PWM for sine wave chopping a few months
>> ago (AKA PWM AC phase control).
>
> Out of interest, how does PWM relate to 'phase control' which AFAIK
> is what dimmer switches use? I'm (probably naively) thinking that
> sine wave chopping is simply turning on and off an AC current with a
> PWM driven switch. Does it have to be locked to the phase of the AC
> supply?
missed the discussion & original post, but maybe the OP is talking about
something like PWM-VSI (voltage source inverter), which uses
uncontrolled dc input (eg just the diodes & capacitor, no voltage
control) and then electronic switches like MOSFETS or IGBT to control
an induction motor. At high switching frequency would look like an
essentially sinusoidal current to the motor (plus a small ripple, of
course).
As for the original question:
>I'm wondering what people are doing to use IGBTs for AC line switching
>(phase control, reverse phase control, and PWM for sine wave chopping). I
>see a couple ways of doing it, but have not seen any ap notes on it (maybe
>a list member can direct me to some)
you might try International Rectifier's AN-937, but I'm not sure about
the implications of AC switching.
>-----Original Message-----
>From: EraseMEpiclist-bouncesspam_OUTTakeThisOuTmit.edu [piclist-bouncesspam_OUTmit.edu]
>Sent: 28 June 2005 20:02
>To: Microcontroller discussion list - Public.
>Subject: RE: [EE] IGBT for AC line switching?
>
>
>At 11:45 AM 6/28/2005, Michael Rigby-Jones wrote:
>
>> >I tried bring up how to do PWM for sine wave chopping a few months
>> >ago (AKA PWM AC phase control).
>>
>>Out of interest, how does PWM relate to 'phase control' which AFAIK is
>>what dimmer switches use? I'm (probably naively) thinking
>that sine wave
>>chopping is simply turning on and off an AC current with a PWM driven
>>switch. Does it have to be locked to the phase of the AC supply?
>
>Ignore that the power supply is a sine wave. Now apply high
>frequency PWM
>to the input, then filter out the PWM components. The output
>is a smaller
>version of the input.
>
>If the PWM frequency is high enough, the fact that the input
>is a sine wave
>doesn't matter. The net result is that the output can be varied by
>changing the PWM duty cycle - even though the output is still a mains
>frequency sine wave.
>
>dwayne
Right, that's exactly what I thought was the theory of operation. However, I can see how this relates in any way to "phase control"?
Regards
Mike
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Hopkins wrote:
> For the light dimmer I made I detected the zero cross point to start my
> timing then turned a traic on after x amount of time to give the
> required amount of brightness.
>
> So yes this was PWM in sync with the mains and I would also say it is
> phase control but not in the sense of altering the incoming phase of the
> mains to some other phase angle or frequency.
What you are doing is commonly called "phase control" because the control is
based on the phase of the AC line. This used to be common in light dimmers
from neolithic times. Back then most lights were incandescent, and there
was a lot less attention to conducted and radiated emissions. This control
scheme only came about because it was easy to implement with triacs or SCRs.
Now we have flourescent lights, tighter emission requirements, and
components that can do high speed (much faster than the AC line frequency)
PWM. Phase control and its nasty spikes is now mostly a historical
footnote.
*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com
Bob S. wrote:
> Hi Harold,
>
> I tried bring up how to do PWM for sine wave chopping a few months ago
> (AKA PWM AC phase control). But certain people on the list server seen
> it as their duty to promote SMPS topologies as the absolute only way to
> do it (the thread went downhill from there)
Maybe because these were your requirements:
Bob S. wrote:
> To put it "simply", here are the basic specs.
>
> 1) Able to generate voltages from 0.3 to 2 volts RMS (AC or DC, I
> don't Care) in at least 256 distinct steps in the output range.
>
> 2) Able to generate over 25 amperes on the output at the top end of
> the range.
>
> 3) Line voltage compensation (output is same for a given setting, no
> matter what the line voltage is reading (90 to 140vac)).
>
> 4) Linear output range (hard to do with AC triac phase control).
>
> 5) It CANNOT generate gobs of heat (again: plastic box, limited sized
> heatsink available, no cooling fans).
>
> 6) It CANNOT generate gobs of RF.
>
> 7) Doesn't have prohibitively high price tag, parts wise.
You gave requirements, many people recommended an SMPS. A 24VAC 2A
transformer rectified & bucked down to your required voltage with
synchronous rectification is the easiest, an offline flyback is the
smallest ... if you merely wanted help with AC phase control you should
have ignored heckling about an SMPS being the best.
OK, since I started the thread long ago and watched it drift off someplace
far away, I'll make a few comments.
We're currently manufacturing triac and SCR (solid state relay) based
light dimmers. They use phase control and have chokes to limit rise time.
I'm looking at alternatives.
#1 is to use FET or IGBT switching and still use phase control or "reverse
phase control" (where we turn the lamp off part way through the AC cycle
intead of turning it on part way through the AC cycle) and varying the
risetime by slowly turning on the FET (resulting in less efficiency, but
we're also dissipating some power in our chokes).
#2 is to use FET or IGBT switching to chop the AC waveform at a high
frequency, then filter out the high frequency. We end up with a sine wave
whose RMS voltage is the incoming RMS voltage times the duty cycle of the
chop voltage.
BOTH of these require the use of one or two IGBTs or FETs to switch the
AC. How are people doing this? Are you using one IGBT or FET and a diode
bridge, or a pair of devices in series with steering diodes around the
"backward" device?
Second, how are the gates being driven? If you use a typical FET driver,
you need a floating power supply for each switched line, which is pretty
complicated. How about pulse transformers to drive the gates? Do you put
clamp circuits to restore the DC component of the drive?
I haven't seen any application notes that describe this.
> >If the PWM frequency is high enough, the fact that the input
> >is a sine wave
> >doesn't matter. The net result is that the output can be varied by
> >changing the PWM duty cycle - even though the output is still a mains
> >frequency sine wave.
>
>Right, that's exactly what I thought was the theory of
>operation. However, I can't see how this relates in any way to "phase
>control"?
Gotcha. Its intended as an alternative to phase control - the idea is that
the high frequency PWM components *might* be a lot easier to filter than
the sharp leading edge caused by phase control.
Celebrating 21 years of Engineering Innovation (1984 - 2005)
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>What you are doing is commonly called "phase control" because the control is
>based on the phase of the AC line. This used to be common in light dimmers
>from neolithic times. Back then most lights were incandescent, and there
>was a lot less attention to conducted and radiated emissions. This control
>scheme only came about because it was easy to implement with triacs or SCRs.
>
>Now we have flourescent lights, tighter emission requirements, and
>components that can do high speed (much faster than the AC line frequency)
>PWM. Phase control and its nasty spikes is now mostly a historical
>footnote.
Hi there, Olin.
I'm not sure if you are speaking "tongue in cheek" but I'm not aware of any
lamp dimmers intended for home use that don't use phase control. Can you
point me towards home-style lamp dimmers that don't use phase control?
Celebrating 21 years of Engineering Innovation (1984 - 2005)
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Dwayne Reid wrote:
> I'm not sure if you are speaking "tongue in cheek" but I'm not aware of
> any lamp dimmers intended for home use that don't use phase control. Can
> you point me towards home-style lamp dimmers that don't use phase
> control?
I don't know about home use. I wasn't referring to existing units in
service either. Do any of those have CE approval? What is the upper power
limit? The industrial AC power designs I've been envolved with in the last
few years have all dealt with high speed switching in there somewhere. Some
have even dealt with power factor correction. The EU maximum power where
you can ignore power factor is well under 100W, something like 70 if I
remember right. If so, a 100W phase controlled dimmed light bulb would
definitely be verboten.
Maybe consumer use phase controlled lamp dimmers are still common here, but
their days must be numbered even so. Florescent lamps often don't deal well
with these kinds of dimmers, or the dimmers don't deal well with the
ballasts. That and the conductive and radiated emissions and I wouldn't
want to invest in new products like that.
*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com
So....using phase control to dim is not the preferred method? Using IGBT for dimming, from what I understand, is more a reverse operation than the standard triac dimming. Not sure. I'd prefer to keep this on the list, as I have an interest in doing dimming using IGBT. Just havent had time to research it.
Olin Lathrop <RemoveMEolin_piclistTakeThisOuTembedinc.com> wrote:
What you are doing is commonly called "phase control" because the control is
based on the phase of the AC line. This used to be common in light dimmers
from neolithic times. Back then most lights were incandescent, and there
was a lot less attention to conducted and radiated emissions. This control
scheme only came about because it was easy to implement with triacs or SCRs.
Now we have flourescent lights, tighter emission requirements, and
components that can do high speed (much faster than the AC line frequency)
PWM. Phase control and its nasty spikes is now mostly a historical
footnote.
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alan smith wrote:
> So....using phase control to dim is not the preferred method? Using
> IGBT for dimming, from what I understand, is more a reverse operation
> than the standard triac dimming.
Triacs are used with phase control only because they rely on the zero
crossings to turn off. Otherwise, whether an IGBT, bipolar, or FET is used
is independent of the control method.
*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com
On Tue, 2005-06-28 at 14:41 -0600, Dwayne Reid wrote:
> At 01:27 PM 6/28/2005, Olin Lathrop wrote:
>
> >What you are doing is commonly called "phase control" because the control is
> >based on the phase of the AC line. This used to be common in light dimmers
> >from neolithic times. Back then most lights were incandescent, and there
> >was a lot less attention to conducted and radiated emissions. This control
> >scheme only came about because it was easy to implement with triacs or SCRs.
> >
> >Now we have flourescent lights, tighter emission requirements, and
> >components that can do high speed (much faster than the AC line frequency)
> >PWM. Phase control and its nasty spikes is now mostly a historical
> >footnote.
>
> Hi there, Olin.
>
> I'm not sure if you are speaking "tongue in cheek" but I'm not aware of any
> lamp dimmers intended for home use that don't use phase control. Can you
> point me towards home-style lamp dimmers that don't use phase control?
Of course that depends on where in the world you are. In NA "phase
control" dimmers are still very common for "smaller" loads (i.e. 250W
and below). With the advent of compact fluorescent lighting they are
getting less popular.
In Europe EMI and power factor regulations are MUCH stricter, I don't
think phase control dimmers are available for anything but the smallest
loads.
At higher power levels phase control is almost completely gone.
However, at the moment, in NA, phase control dimming in residential
smaller power applications is still the big one, and certainly not yet a
"historical footnote".
On Tue, 2005-06-28 at 17:39 -0400, Olin Lathrop wrote:
> Maybe consumer use phase controlled lamp dimmers are still common here, but
> their days must be numbered even so. Florescent lamps often don't deal well
> with these kinds of dimmers, or the dimmers don't deal well with the
> ballasts. That and the conductive and radiated emissions and I wouldn't
> want to invest in new products like that.
Guess you haven't been to your local Home Depot? :)
There are now compact fluorescent models that are compatible with phase
control dimmers! They don't work that well (they only dim a certain
amount), and they are VERY expensive, but they are there, and getting
more common.
And yet, NOBODY has attempted to answer his question(s), which he has
now clarified a bit more. Dwayne Reid "got it", in that this is
intended as an ALTERNATIVE to "Phase control". So stop talking about
phase control, triacs, SMPS's, etc....
So please read Harold's original post, his current post (below), maybe a
few of Dwayne's posts; and then reply if you have something of substance
to offer.
BTW, setting it up with a single IGBT/FET with a diode bridge is
probably easier/better, as you don't have to worry what state (on/off)
your IGBT/FET is in during ZC. I don't "think" you could have a pair of
IGBT/FETS in series setup, and have both of them turned on at the same
time without some problems cropping up. Also, the problem with "reverse
phase control" (#1 method below) is that you can't use it on an
inductive load, where as in the #2 method it doesn't matter. As to
driving the gate(s), that's where I got stumped too....
>OK, since I started the thread long ago and watched it drift off someplace
>far away, I'll make a few comments.
>
>We're currently manufacturing triac and SCR (solid state relay) based
>light dimmers. They use phase control and have chokes to limit rise time.
>I'm looking at alternatives.
>
>#1 is to use FET or IGBT switching and still use phase control or "reverse
>phase control" (where we turn the lamp off part way through the AC cycle
>intead of turning it on part way through the AC cycle) and varying the
>risetime by slowly turning on the FET (resulting in less efficiency, but
>we're also dissipating some power in our chokes).
>
>#2 is to use FET or IGBT switching to chop the AC waveform at a high
>frequency, then filter out the high frequency. We end up with a sine wave
>whose RMS voltage is the incoming RMS voltage times the duty cycle of the
>chop voltage.
>
>BOTH of these require the use of one or two IGBTs or FETs to switch the
>AC. How are people doing this? Are you using one IGBT or FET and a diode
>bridge, or a pair of devices in series with steering diodes around the
>"backward" device?
>
>Second, how are the gates being driven? If you use a typical FET driver,
>you need a floating power supply for each switched line, which is pretty
>complicated. How about pulse transformers to drive the gates? Do you put
>clamp circuits to restore the DC component of the drive?
>
>I haven't seen any application notes that describe this.
>
>THANKS!
>
>Harold
>
>
>
>
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At 11:51 AM 6/29/2005 -0500, you wrote:
>And yet, NOBODY has attempted to answer his question(s), which he has now
>clarified a bit more. Dwayne Reid "got it", in that this is intended as
>an ALTERNATIVE to "Phase control". So stop talking about phase control,
>triacs, SMPS's, etc....
>So please read Harold's original post, his current post (below), maybe a
>few of Dwayne's posts; and then reply if you have something of substance
>to offer.
>
>BTW, setting it up with a single IGBT/FET with a diode bridge is probably
>easier/better, as you don't have to worry what state (on/off) your
>IGBT/FET is in during ZC. I don't "think" you could have a pair of
>IGBT/FETS in series setup, and have both of them turned on at the same
>time without some problems cropping up. Also, the problem with "reverse
>phase control" (#1 method below) is that you can't use it on an inductive
>load, where as in the #2 method it doesn't matter. As to driving the
>gate(s), that's where I got stumped too....
One obvious way is to use (a) photovoltaic optoisolator(s).
> One obvious way is to use (a) photovoltaic optoisolator(s).
I don't they're fast enough and don't have enough output current
capability to quickly drive the gate, especially considering Miller
effect. I could be wrong , though (it's been known to happen).
On 6/29/05, Harold Hallikainen <TakeThisOuTharoldEraseMEspam_OUThallikainen.com> wrote:
>
> > One obvious way is to use (a) photovoltaic optoisolator(s).
>
>
> I don't they're fast enough and don't have enough output current
> capability to quickly drive the gate, especially considering Miller
> effect. I could be wrong , though (it's been known to happen).
>
> Harold
>
Not the old-fashioned optos, but the special purpose ones like
HCPL-3140 work great for this.
Regards,
Mark
markrages
--
You think that it is a secret, but it never has been one.
- fortune cookie
> On 6/29/05, Harold Hallikainen <RemoveMEharoldTakeThisOuThallikainen.com> wrote:
>>
>> > One obvious way is to use (a) photovoltaic optoisolator(s).
>>
>>
>> I don't they're fast enough and don't have enough output current
>> capability to quickly drive the gate, especially considering Miller
>> effect. I could be wrong , though (it's been known to happen).
>>
>> Harold
>>
>
> Not the old-fashioned optos, but the special purpose ones like
> HCPL-3140 work great for this.
>
Thanks!
That doesn't appear to be a photovoltaic in that it requires a DC supply
on the line side of the opto. If we have lots of channels, that's a lot of
floating power supplies. http://cp.literature.agilent.com/litweb/pdf/5989-2138EN.pdf
>Thanks!
>That doesn't appear to be a photovoltaic in that it requires a DC supply
>on the line side of the opto. If we have lots of channels, that's a lot of
>floating power supplies.
>
> > On 6/29/05, Harold Hallikainen <RemoveMEharoldEraseMEEraseMEhallikainen.com> wrote:
> >>
> >> > One obvious way is to use (a) photovoltaic optoisolator(s).
> >>
> >>
> >> I don't they're fast enough and don't have enough output current
> >> capability to quickly drive the gate, especially considering Miller
> >> effect. I could be wrong , though (it's been known to happen).
> >>
> >> Harold
> >>
> >
> > Not the old-fashioned optos, but the special purpose ones like
> > HCPL-3140 work great for this.
> >
>
> Thanks!
> That doesn't appear to be a photovoltaic in that it requires a DC supply
> on the line side of the opto. If we have lots of channels, that's a lot of
> floating power supplies.
> cp.literature.agilent.com/litweb/pdf/5989-2138EN.pdf
>
> Harold
Right. I used a simple resistor+zener supply in my application. (15V
zener, 15k resistor, 0.1 uF across the zener. rectified 117 VAC, 20kHz
PWM, IRF740)
Regards,
Mark
markrages@gmail
--
You think that it is a secret, but it never has been one.
- fortune cookie
> At 11:36 AM 6/29/2005 -0700, you wrote:
>
>
>>Thanks!
>>That doesn't appear to be a photovoltaic in that it requires a DC supply
>>on the line side of the opto. If we have lots of channels, that's a lot
>> of
>>floating power supplies.
>
> Here's a typical one:
>
> http://www.irf.com/product-info/datasheets/data/pvin.pdf
>
> They should be fast enough for reverse phase control, but not for PWM
> at any reasonable speed.
>
Thanks! Short circuit output current is about 17uA. This seems like a
pretty low gate drive for a FET or IGBT switching substantial voltage when
considering Miller effect. Comments?
> On 6/29/05, Harold Hallikainen <RemoveMEharoldspam_OUTKILLspamhallikainen.com> wrote:
>>
>> > On 6/29/05, Harold Hallikainen <RemoveMEharoldTakeThisOuTspamhallikainen.com> wrote:
>> >>
>> >> > One obvious way is to use (a) photovoltaic optoisolator(s).
>> >>
>> >>
>> >> I don't they're fast enough and don't have enough output current
>> >> capability to quickly drive the gate, especially considering Miller
>> >> effect. I could be wrong , though (it's been known to happen).
>> >>
>> >> Harold
>> >>
>> >
>> > Not the old-fashioned optos, but the special purpose ones like
>> > HCPL-3140 work great for this.
>> >
>>
>> Thanks!
>> That doesn't appear to be a photovoltaic in that it requires a DC supply
>> on the line side of the opto. If we have lots of channels, that's a lot
>> of
>> floating power supplies.
>> cp.literature.agilent.com/litweb/pdf/5989-2138EN.pdf
>>
>> Harold
>
> Right. I used a simple resistor+zener supply in my application. (15V
> zener, 15k resistor, 0.1 uF across the zener. rectified 117 VAC, 20kHz
> PWM, IRF740)
>
OK, I see that as a possibility. Did you use a single device and a bridge
rectifier, or two devices with steering diodes?
They're called MGD's or MOS-Gate Drivers, and certain "high side"
versions can be used for Mosfets or IGBT's as driving circuits. Some
versions are designed to be used with current sense IGBTs too.
Let me know if this is what you've been looking for.
>>On 6/29/05, Harold Hallikainen <EraseMEharoldspamspamBeGonehallikainen.com> wrote:
>>
>>
>>>>One obvious way is to use (a) photovoltaic optoisolator(s).
>>>>
>>>>
>>>I don't they're fast enough and don't have enough output current
>>>capability to quickly drive the gate, especially considering Miller
>>>effect. I could be wrong , though (it's been known to happen).
>>>
>>>Harold
>>>
>>>
>>>
>>Not the old-fashioned optos, but the special purpose ones like
>>HCPL-3140 work great for this.
>>
>>
>>
>
>Thanks!
>That doesn't appear to be a photovoltaic in that it requires a DC supply
>on the line side of the opto. If we have lots of channels, that's a lot of
>floating power supplies.
>http://cp.literature.agilent.com/litweb/pdf/5989-2138EN.pdf
>
>Harold
>
>
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On 6/29/05, Harold Hallikainen <RemoveMEharoldKILLspamhallikainen.com> wrote:
>
> >
> > Right. I used a simple resistor+zener supply in my application. (15V
> > zener, 15k resistor, 0.1 uF across the zener. rectified 117 VAC, 20kHz
> > PWM, IRF740)
> >
>
> OK, I see that as a possibility. Did you use a single device and a bridge
> rectifier, or two devices with steering diodes?
>
> Harold
Actually, I was driving a universal motor, so I used a bridge
rectifier and a single device in series with the motor inside the
bridge. This gave me a 160VDC supply. (there was no filter capacitor
on this supply, so it was 120 Hz pulsed "DC".)
Unless your load can take DC, this arrangement is not gonna work for
you. I don't think it would be too hard to modify it to move the load
outside the bridge. I think you'd just need to add a diode to the
resistor+zener.
Regards,
Mark
markrages@gmail
--
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Thanks! The high side drivers are used in H bridge or half bridge DC
switching circuits. In their example circuits, there is a common ground
between the control input and the HV supply. I'm really looking for
something like an IGBT AC solid state relay, similar to the SCR solid
state relays. I apply voltage to an isolated input and the output shorts.
I remove voltage and the output opens. Getting the opto isolation
generally requires a floating supply to drive the gate. As another poster
noted, that supply can possibly be pretty simple (diode, resistor,
capactior, and zener). There's a nice table at the end of the first apnote
(
www.powerdesigners.com/InfoWeb/design_center/Appnotes_Archive/an-978.pdf
) that summarizes driving floating devices. It seems that the pulse
transformer with a clamp to restore DC on the high voltage side could be
used. The "carrier drive" method seems like it'd have slow turn off. The
bootstrap method doesn't seem like it'd work if the duty cycle is 100%.
So... I'm leaning towards a opto isolated FET driver driven powered by a
simple transformerless power supply on the AC line side. It seems simplest
to use a diode bridge between the line and load with the FET or IGBT on
the "DC side" of the bridge. Our voltage drops are starting to accumulate,
though. We've got at least 1.4V across the bridge, plus what, another volt
or two across the IGBT?
On 29 Jun 2005 at 15:03, Harold Hallikainen wrote:
> So... I'm leaning towards a opto isolated FET driver driven powered by a
> simple transformerless power supply on the AC line side. It seems simplest
> to use a diode bridge between the line and load with the FET or IGBT on
> the "DC side" of the bridge. Our voltage drops are starting to accumulate,
> though. We've got at least 1.4V across the bridge, plus what, another volt
> or two across the IGBT?
I have used a very similar circuit with an IRF740 inside a
diode bridge driven by a 4N25 optocoupler. A diode + resistor + 15V zener
+ capacitor made the gate power supply.
At 10kHz the switching was ok, very little heat on the MOSFET at 200W
resistive load.
Take a look at the IR2110 datasheet once, I think that is similar to
what you want. It doesn't require optical isolation, as the driver has
an internal level shifter.
Yea, you loose a couple of volts with an IGBT, but at least that is a
constant no matter what the current draw is, where as a mosfet voltage
drop goes up more and more as you draw more current (an IGBT should be
linear throughout the PWM range).
>Thanks! The high side drivers are used in H bridge or half bridge DC
>switching circuits. In their example circuits, there is a common ground
>between the control input and the HV supply. I'm really looking for
>something like an IGBT AC solid state relay, similar to the SCR solid
>state relays. I apply voltage to an isolated input and the output shorts.
>I remove voltage and the output opens. Getting the opto isolation
>generally requires a floating supply to drive the gate. As another poster
>noted, that supply can possibly be pretty simple (diode, resistor,
>capactior, and zener). There's a nice table at the end of the first apnote
>(
>www.powerdesigners.com/InfoWeb/design_center/Appnotes_Archive/an-978.pdf
>) that summarizes driving floating devices. It seems that the pulse
>transformer with a clamp to restore DC on the high voltage side could be
>used. The "carrier drive" method seems like it'd have slow turn off. The
>bootstrap method doesn't seem like it'd work if the duty cycle is 100%.
>
>So... I'm leaning towards a opto isolated FET driver driven powered by a
>simple transformerless power supply on the AC line side. It seems simplest
>to use a diode bridge between the line and load with the FET or IGBT on
>the "DC side" of the bridge. Our voltage drops are starting to accumulate,
>though. We've got at least 1.4V across the bridge, plus what, another volt
>or two across the IGBT?
>
>Harold
>
>
>
>
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> On 29 Jun 2005 at 15:03, Harold Hallikainen wrote:
>
>> So... I'm leaning towards a opto isolated FET driver driven powered by a
>> simple transformerless power supply on the AC line side. It seems
>> simplest
>> to use a diode bridge between the line and load with the FET or IGBT on
>> the "DC side" of the bridge. Our voltage drops are starting to
>> accumulate,
>> though. We've got at least 1.4V across the bridge, plus what, another
>> volt
>> or two across the IGBT?
>
> I have used a very similar circuit with an IRF740 inside a
> diode bridge driven by a 4N25 optocoupler. A diode + resistor + 15V zener
> + capacitor made the gate power supply.
> At 10kHz the switching was ok, very little heat on the MOSFET at 200W
> resistive load.
>
> Mark Jordan
>
>
>
mit.edu [.....piclist-bouncesKILLspam
