Hi,
I need to drive a DC 1/8 HP DC motor via PWM using a 16c74.My problem is
which transistors I should use to do this and how to trigger them.I have read
something on IGBT being used in power inverters,but I have also been told
they are somewhat more complicated to trigger than a regular MOSFET.
Could someone tell me what's my best choice?
Thanks.
> Hi,
> I need to drive a DC 1/8 HP DC motor via PWM using a 16c74.My problem is
> which transistors I should use to do this and how to trigger them.I have read
> something on IGBT being used in power inverters,but I have also been told
> they are somewhat more complicated to trigger than a regular MOSFET.
> Could someone tell me what's my best choice?
What's the current? I would personally go with MOSFETs (thanks to
all who helped me with this last month), because driving a MOSFET is
pretty trivial, with one caveat: the load, looking into the gate is
capacitive, so it draws virtually no current at steady state, but can draw
(or sink) a much larger amount during turn-on and turn-off (when dI/dt is
large). That said, IRF carries a full range of power MOSFETs, some with
absolutely ridiculously low on-resistance.
Pierce Nichols
"I have a work order for the immediate demolition of your reality tunnel."
<<
Hi,
I need to drive a DC 1/8 HP DC motor via PWM using a 16c74.My problem is
which transistors I should use to do this and how to trigger them.I have
read
something on IGBT being used in power inverters,but I have also been told
they are somewhat more complicated to trigger than a regular MOSFET.
Could someone tell me what's my best choice?
Thanks.
>>
What is the voltage you need to drive it from ?
The higher the DC voltage the lower the current.
To drive Lager IGBT look out the siliconex SI9910DJ Mosfet driver IC It comes
complete with desaturation protection. You will need to add a PNP transistor
to turn off the IGBT as it can take sevrel amps to discharge the Miller
capacitor. The whole circuit works from 15V and this can be derived from a
single supply using a fast diode for the High side driver dont forget the
opto couplers that drive these will have to be reasnoably fast we use H11
units with smhidt but most fast ones are ok. If you are worried about DIY
drivers look at Semikron SKHI200 this is a universal twin output driver which
will drive IGBT's up to 400A and 1200V.
At 16:06 10/11/97 -0500, you wrote:
>On Mon, 10 Nov 1997, Walter Markiw wrote:
>
>> Hi,
>> I need to drive a DC 1/8 HP DC motor via PWM using a 16c74.My problem is
>> which transistors I should use to do this and how to trigger them.I have read
>> something on IGBT being used in power inverters,but I have also been told
>> they are somewhat more complicated to trigger than a regular MOSFET.
>> Could someone tell me what's my best choice?
>
> What's the current? I would personally go with MOSFETs (thanks to
>all who helped me with this last month), because driving a MOSFET is
>pretty trivial, with one caveat: the load, looking into the gate is
>capacitive, so it draws virtually no current at steady state, but can draw
>(or sink) a much larger amount during turn-on and turn-off (when dI/dt is
>large). That said, IRF carries a full range of power MOSFETs, some with
>absolutely ridiculously low on-resistance.
>
Thanks a lot for having answered so fast,Pierce.
The current shouldn't go further than 2 amp.,or 10 amp.considering the
start (nominal current X 5)(220 v DC).I have been told about IRF P350
transistors, 400 v,15 amp.,125w dissipation.However,I found that I can't
push PWM duty cycle further than 75 % of the period (I am using a 10 khz
PWM,which gives a 100 us period),what means that for some obscure reason -to me-
the transistor is not able to turn off and on again in less than 25 us.Should
that be that way,or is there something I'm missing -which is undoubtably truth-
about triggering those mosfets?
Anyhow,I would like to learn something on triggering IGBTs,if anyone outthere
could show me how to trigger them,I would be thankful.
>In a message dated 10/11/97 21:05:51, you write:
>
><<
> Hi,
> I need to drive a DC 1/8 HP DC motor via PWM using a 16c74.My problem is
> which transistors I should use to do this and how to trigger them.I have
>read
> something on IGBT being used in power inverters,but I have also been told
> they are somewhat more complicated to trigger than a regular MOSFET.
> Could someone tell me what's my best choice?
> Thanks.
> >>
>What is the voltage you need to drive it from ?
>The higher the DC voltage the lower the current.
>
>To drive Lager IGBT look out the siliconex SI9910DJ Mosfet driver IC It comes
>complete with desaturation protection. You will need to add a PNP transistor
>to turn off the IGBT as it can take sevrel amps to discharge the Miller
>capacitor. The whole circuit works from 15V and this can be derived from a
>single supply using a fast diode for the High side driver dont forget the
>opto couplers that drive these will have to be reasnoably fast we use H11
>units with smhidt but most fast ones are ok. If you are worried about DIY
>drivers look at Semikron SKHI200 this is a universal twin output driver which
>will drive IGBT's up to 400A and 1200V.
>
>Cheers Steve.....
>
>
Voltage is 220 volts.How I can trigger an IGBT using a pic,without a
dedicated driver?Have you ever tried that?I don't need much current,since
at 220 volt,1/4 HP (aprox 190 w) would be less than 1 amp.Even when starting
the motor shouldn't take more than 5 amps.
> > What's the current? I would personally go with MOSFETs (thanks to
> >all who helped me with this last month), because driving a MOSFET is
> >pretty trivial, with one caveat: the load, looking into the gate is
> >capacitive, so it draws virtually no current at steady state, but can draw
> >(or sink) a much larger amount during turn-on and turn-off (when dI/dt is
A small mistake here -- dI(gate)/dt is proportional to
dV(gate)/dt.
> The current shouldn't go further than 2 amp.,or 10 amp.considering the
> start (nominal current X 5)(220 v DC).I have been told about IRF P350
> transistors, 400 v,15 amp.,125w dissipation.However,I found that I can't
> push PWM duty cycle further than 75 % of the period (I am using a 10 khz
> PWM,which gives a 100 us period),what means that for some obscure reason -to
me-
> the transistor is not able to turn off and on again in less than 25 us.Should
> that be that way,or is there something I'm missing -which is undoubtably
truth-
> about triggering those mosfets?
It prob. means you need to be able to supply more current into the
gate of the mosfet on turn-on and sink more on turn-off. There is another
limit, but the one imposed by the gate (Miller) capacitance is the one
that's prob. getting you. Out of curiosity, what source/sink current can
you put on the gate of the MOSFET?
Pierce
"I have a work order for the immediate demolition of your reality tunnel."
> Voltage is 220 volts.How I can trigger an IGBT using a pic,without a
> dedicated driver?Have you ever tried that?I don't need much current,since
> at 220 volt,1/4 HP (aprox 190 w) would be less than 1 amp.Even when starting
> the motor shouldn't take more than 5 amps.
You're going to need a driver for either one -- power MOSFETs
generally have a threshold of around 5V, and to get full conduction, you
need more like 12V-15V on the gate. They also source/sink a *lot* of
current when switching state -- the faster the transition, the more
current. It's just the typical voltage current relation for a capacitance,
tho, b/c the gate is a capacitive load.
Pierce
"I have a work order for the immediate demolition of your reality tunnel."
At 07:29 PM 11/10/97 -0500, you wrote:
>On Mon, 10 Nov 1997, Walter Markiw wrote:
>
>> > What's the current? I would personally go with MOSFETs (thanks to
>> >all who helped me with this last month), because driving a MOSFET is
>> >pretty trivial, with one caveat: the load, looking into the gate is
>> >capacitive, so it draws virtually no current at steady state, but can draw
>> >(or sink) a much larger amount during turn-on and turn-off (when dI/dt is
>
> A small mistake here -- dI(gate)/dt is proportional to
>dV(gate)/dt.
Don't you mean I(gate) is proportional to dV(gate)/dt?
For a cap. load:
Q=CV
differentiate both sides:
dQ/dt = C dV/dt
dQ/dt = I
therefore:
I = C dV/dt
I am curious about one thing: What are the major differences between IGBTs
and MOSFETS? Lower Rds(on)?
Sean
Sean Breheny,KA3YXM
Electrical Engineering Student
Walter! how timely. I just finished a DC motor speed controller for a client
and
they rejected it. I met all of the design goals, and my downfall was a very
slight ripple on the voltage on the motor. So slight that you could not see the
variation in shaft motor. The motors were Japanese, though, and not rated
horsepower. I designed for two motors, a 45 volt and a 21 volt (same
controller). I did a bang up job of controlling torque by monitoring back EMF
on
the motor and comparing to command signal. I used PI (skipped D) to perform
feedback. I actually used a MOSFET, and when a very heavy load was put on the
motor, the controller shot current so high that I burnt paint off of the PCB. I
had to use a lower RDSon FET and implement current limitting. The answer to
your
question is International Rectifier part IRF3710. And 100 mil traces through
the
current path.
There are other details, but I'll let you in on the biggest revelation. You
must
sample the motor voltage just before you begin your PWM on phase. This way the
voltage has settled to as close to free wheel EMF as possible. And you must PWM
much slower than the built in PWM so that this settling takes place. I found 60
to 120 Hz to be ideal.
Best of luck, need any more advice I'll throw in what I know.
Chris Eddy
Pioneer Microsystems, Inc.
Pittsburgh, PA
Walter Markiw wrote:
> Hi,
> I need to drive a DC 1/8 HP DC motor via PWM using a 16c74.My problem is
> which transistors I should use to do this and how to trigger them.I have read
> something on IGBT being used in power inverters,but I have also been told
> they are somewhat more complicated to trigger than a regular MOSFET.
> Could someone tell me what's my best choice?
> Thanks.
>I am curious about one thing: What are the major differences between IGBTs
>and MOSFETS? Lower Rds(on)?
>
>Sean
Yes, very low Rds on - minimizes heat-sink requirements.
Postive temp coefficient (turns OFF as it gets hotter, rather than the
other way around ala Bipolar, so avoids thermal runaway).
Almost infinite power gain at low switching rates.
Extremely fast turn-on and turn-off at hi currents, maximizes switching
power supply efficiency.
But -- exceed the maximim gate-source voltage for a nanosecond and kiss it
goodby.
On Mon, 10 Nov 1997 20:20:53 -0800 Ron Fial <spam_OUTronTakeThisOuTFIAL.COM> writes:
>>I am curious about one thing: What are the major differences between
>IGBTs
>>and MOSFETS? Lower Rds(on)?
>>
>>Sean
>
>Yes, very low Rds on - minimizes heat-sink requirements.
>Postive temp coefficient (turns OFF as it gets hotter, rather than the
> other way around ala Bipolar, so avoids thermal runaway).
As I understand it, an IGBT consists of a MOSFET driving a bipolar in a
Darlington configuration:
C
||-----|
NFET|| |
B---||-| | /c
--| NPN
\ | \e
Res/ |
\---|
E
Power FETs that can withstand higher Vds (off) voltage are hard to make
without increasing Rds (on) a lot. Thus they don't have much current
capacity. For high-voltage, high-current circuits, the IGBT was
designed. The NPN acts as a current booster, so the FET only has to
handle a small proportion of the total current being switched. The input
to an IGBT has the same large capacitance, zero DC current
characteristics of a FET (since it is a FET). The same driver circuit can
be used. The configuration also prevents the bipolar from going into
full saturation, allowing it to turn off quickly. I think a resistor is
integrated as I've drawn it to help the bipolar switch off.
But the IGBT has an unavoidable on-state saturation voltage of a couple
of volts (VBE of the bipolar plus the resistance loss in the FET). This
voltage is relatively independent of the drain/ collector current. In a
circuit using hundreds or thousands of volts, a couple of volts switching
loss isn't too bad. But at low voltages, a regular FET will do better,
since the silicon can be designed for low on-resistance. Conduction loss
in the FET circuit is easy to analyze by assuming the switched-on device
is a resistor. The IGBT is more complicated and nonlinear.
I've been looking for a way to get around the saturation voltage
of triacs and have considered FETs and IGBTs for AC switching. It SEEMS
to me that the saturation voltage on an IGBT is going to be higher than
that of a FET. I view an IGBT as a sort of darlington with an FET as the
first transistor. Is this correct? If so, the input FET can go to a
source-drain short and we still need 700 mV or so on the collector to
turn on the base. Seems that directly driving the gate of a FET would
give us lower voltage drop (just due to Rds on).
In AC applications, I've thought of putting two FETs in series
and using the intrinisic diodes to steer the current into the appropriate
FET. Again, we'll lose about 700 mV across the diode of the FET that is
being bypassed. It seems that the voltage drop will be approaching that
of a triac, and we have increased circuit conplexity to boot!
Walter Markiw wrote:
>
> Hi,
> I need to drive a DC 1/8 HP DC motor via PWM using a 16c74.My problem is
> which transistors I should use to do this and how to trigger them.I have read
> something on IGBT being used in power inverters,but I have also been told
> they are somewhat more complicated to trigger than a regular MOSFET.
> Could someone tell me what's my best choice?
> Thanks.
I used logic level mosfet worked fine with 5k pwm.
Doesn't answer all your questions, but International Rectifier App note
AN-983 gives a good explanation of how an IGBT works
(http://www.irf.com/search/).
Ron
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Ron Kreymborg Computer Systems Manager
Monash University CRC for Southern Hemisphere Meteorology
Wellington Road
Clayton, VIC 3168 Phone : 061-3-9905-9671
Australia Fax : 061-3-9905-9689
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> I've been looking for a way to get around the saturation voltage
> of triacs and have considered FETs and IGBTs for AC switching. It SEEMS
> to me that the saturation voltage on an IGBT is going to be higher than
> that of a FET. I view an IGBT as a sort of darlington with an FET as the
> first transistor. Is this correct? If so, the input FET can go to a
> source-drain short and we still need 700 mV or so on the collector to
> turn on the base. Seems that directly driving the gate of a FET would
> give us lower voltage drop (just due to Rds on).
> In AC applications, I've thought of putting two FETs in series
> and using the intrinisic diodes to steer the current into the appropriate
> FET. Again, we'll lose about 700 mV across the diode of the FET that is
> being bypassed. It seems that the voltage drop will be approaching that
> of a triac, and we have increased circuit conplexity to boot!
>
> Harold
>
>I am curious about one thing: What are the major differences between IGBTs
>and MOSFETS? Lower Rds(on)?
In on state, MOSFET behaves like a resistor: Uds=I*Ron, P=Uds*I=Ron*I^2.
At the other hand, IGBT is like a saturated transistor, Uce is almost
independent of colector current: Uce=const, P=const*I. The advantage of IGBT
shows at very high current (talking hundreds of amps), and it can also
withstand higher voltages in off state.
Pioneer Microsystems wrote:
>
> Walter! how timely. I just finished a DC motor speed controller for a client
> and
> they rejected it. I met all of the design goals, and my downfall was a very
> slight ripple on the voltage on the motor. So slight that you could not see
the {Quote hidden}
> variation in shaft motor. The motors were Japanese, though, and not rated
> horsepower. I designed for two motors, a 45 volt and a 21 volt (same
> controller). I did a bang up job of controlling torque by monitoring back EMF
> on
> the motor and comparing to command signal. I used PI (skipped D) to perform
> feedback. I actually used a MOSFET, and when a very heavy load was put on the
> motor, the controller shot current so high that I burnt paint off of the PCB.
I
> had to use a lower RDSon FET and implement current limitting. The answer to
> your
> question is International Rectifier part IRF3710. And 100 mil traces through
> the
> current path.
>
> There are other details, but I'll let you in on the biggest revelation. You
> must
> sample the motor voltage just before you begin your PWM on phase. This way
the
> voltage has settled to as close to free wheel EMF as possible. And you must
PWM
> much slower than the built in PWM so that this settling takes place. I found
60
> to 120 Hz to be ideal.
>
> Best of luck, need any more advice I'll throw in what I know.
>
> Chris Eddy
> Pioneer Microsystems, Inc.
> Pittsburgh, PA
>
Chris it's a bit late I know but I saved this thread to look at closely
when I had time (which is now)
I am about to start on a dc motor speed controler
for an 150 watt x 15 Volt motor
the motor draws about 10 amps working continuously
up to 8 Hours and 60 Amps stall which happens often
A slow pmw rate would not be a problem.
Monitoring back EMF would be overkill in this
application (though I would like to know how it's done)
I will monitor the current instead( the wires to the motor
are at least 5 Meters ) using the voltage drop on one
of the motor wires using three core replacing the existing
two core cable.
The third wire can then also be used to start/stop the motor
and change the speed
I intend to use a 16x84
using cap charge time to measure the cable(and maybe fet)
drop voltage drop ( > 8 amps is all I need, mostly over current
shutdown/foldback )
Any help on what fet's
how best to drive them
any other advice
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