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Which MOSFET / IGBT can afford 5A current normal operation and 40A current at 1-2 seconds?

E

Electronic Swear

Jan 1, 1970
0
I am considering to use a transister to be a switch for over current
cut-off. It is controlling a 220AC(rectified)DC motor and monitoring
it go over current or not. At normal operation, motor current is 5A.
However, if it is over current, it maybe rise to 40A at 1-2 seconds
and transistor will be cut-off.

Which MOSFET / IGBT can afford 5A current normal operation and 40A
current at 1-2 seconds and VDS need > 400V ? Of course, price is one
of the most important parameter for me. But I think functionable is
the most important part.
 
W

Winfield Hill

Jan 1, 1970
0
Electronic Swear wrote...
I am considering to use a transister to be a switch for over current
cut-off. It is controlling a 220AC(rectified)DC motor and monitoring
it go over current or not. At normal operation, motor current is 5A.
However, if it is over current, it maybe rise to 40A at 1-2 seconds
and transistor will be cut-off.

Which MOSFET / IGBT can afford 5A current normal operation and 40A
current at 1-2 seconds and VDS need > 400V ? Of course, price is one
of the most important parameter for me. But I think functionable is
the most important part.

There are many candidates for a job like that, but if you can get
a pair in a SOT-227B power case, with insulated heat-sink plates,
that would be good. Fairchild's 600V 40 IGBT, HGT1N40N60A4D, is a
good example, http://www.fairchildsemi.com/pf/HG/HGT1N40N60A4D.html
It's actually a bit better than you need. It will drop 1.4V at 5A,
rising to 2.1V at 40A, disspating only 84 of its rated 300 watts.

To make a AC switch you'll need to drive two such IGBTs back-to-back
(with sources and gates connected) using a floating drive circuit.
 
F

Fritz Schlunder

Jan 1, 1970
0
Electronic Swear said:
I am considering to use a transister to be a switch for over current
cut-off. It is controlling a 220AC(rectified)DC motor and monitoring
it go over current or not. At normal operation, motor current is 5A.
However, if it is over current, it maybe rise to 40A at 1-2 seconds
and transistor will be cut-off.

Which MOSFET / IGBT can afford 5A current normal operation and 40A
current at 1-2 seconds and VDS need > 400V ? Of course, price is one
of the most important parameter for me. But I think functionable is
the most important part.


Greetings.

There are many ways to skin this cat. If you can tolerate a "live" heatsink
(or in this case more of a heatspreader), then I think I might suggest
paralleling three or perhaps four IRFP460P MOSFETs:

http://www.irf.com/product-info/datasheets/data/irfp460p.pdf

For some reason these are surprisingly cheap and offer quite decent bang for
the buck (at least compared to a number of other Digikey offerings). They
are TO-247 parts rated at 500V, 0.27 Ohm on resistance, and 280W power
dissipation. The novelty of this solution (compared to IGBT solutions) is
that the normal power dissipation at 5A will be quite minimal. Of course,
you will still need a nice heatsink/heatspreader with minimal thermal
resistance between the TO-247 case and heatsink to safely handle the 40A
fault current.
 
E

Electronic Swear

Jan 1, 1970
0
Thank you for your suggestion.

Basically, I have tried to use IRFP450 before. Of course there is
a heatsink behind the body of the transistor. However, it is also
failure in that operation. At 40A current 1-2 seconds, the transistor
cannot switch to cut-off. Then the transistor finally burnt out with
short the junction.

If I use for the IRFP460, what size of heatsink should I need for?
Topically, the IRFP460 is not much affordable a higher current then
IRFP450. So, is it also afford that high current at 40A?
 
W

Winfield Hill

Jan 1, 1970
0
Electronic Swear wrote...
Thank you for your suggestion.

Basically, I have tried to use IRFP450 before. Of course there is
a heatsink behind the body of the transistor. However, it is also
failure in that operation. At 40A current 1-2 seconds, the transistor
cannot switch to cut-off. Then the transistor finally burnt out with
short the junction.

Of course the usual answer, and not a bad one, is to use a mechanical
switch, such as a contactor. But if you must use an electronic switch
for some reason, you might consider the parallel combination of a FET
and a high-current IGBT (but perhaps a smaller one than I suggested).
This can give you the best of both worlds. (At higher AC currents one
can consider using a large GTO (gate-turn-off) thyristor.)
If I use for the IRFP460, what size of heatsink should I need for?
Topically, the IRFP460 is not much affordable a higher current then
IRFP450. So, is it also afford that high current at 40A?

As you know, the IRF450 is a 0.4-ohm FET, and the IRF460 is a 0.27-ohm
part. So a '450 will heat 50% more than a '460, which is significant.

Back to a '460, we know its 0.27-ohm Ron will be increased by 2.3x for
a hot die temp. Consider P=I^2R for 40A with 0.27*2.3 ohms = 933 watts.
Even though we have some thermal mass working in our favor, we can see
that a '460 FET, through an insulator to a cool heatsink, can still get
us into serious trouble during a several-seconds long event. (A quick
examination of the Effective Transient Thermal Impedance plot shows the
benefit of the FET die's thermal mass is gone well before two seconds.)
 
E

Electronic Swear

Jan 1, 1970
0
You are right.
Initially, I want to use relay as a switch.
When the current up to 40A, my control circuit try to
switch-off the relay, however, it cannot be switch-off
even there are a control signal to trigger.

The problem is if I want to control a relay the switch-off
from 40A current, the relay cannot be switch-off because of
the high attractive force by high current.

I don't know why there are such kind of problems. I use a
10A relay, but the problem still happen. When I change to
use a very large size AC relay, then it can trip-off. It
is not possible for me to choose large side component for
built-in my product.
 
T

Tony Williams

Jan 1, 1970
0
Winfield Hill said:
Of course the usual answer, and not a bad one, is to use a
mechanical switch, such as a contactor.
[snip]

Yes, the more usual solution would be a motor-rated
AC circuit breaker upstream of the rectifying bridge.

See Farnell 717-5670, at GBP 9 pounds.

This is an ABB circuit breaker which will carry 6Arms
permanently without tripping, and will allow 48-72Arms
to flow for about one second before tripping.

For a single phase rectifier without capacitive smoothing
divide those AC currents by 1.1 to get the approx DC. So
that would be 5.5Adc carry-current, tripping after one
second at 44 to 65Adc.
 
F

Fritz Schlunder

Jan 1, 1970
0
Electronic Swear said:
Thank you for your suggestion.

Basically, I have tried to use IRFP450 before. Of course there is
a heatsink behind the body of the transistor. However, it is also
failure in that operation. At 40A current 1-2 seconds, the transistor
cannot switch to cut-off. Then the transistor finally burnt out with
short the junction.

If I use for the IRFP460, what size of heatsink should I need for?
Topically, the IRFP460 is not much affordable a higher current then
IRFP450. So, is it also afford that high current at 40A?


A single IRFP450 device will not be adequate, regardless of the size of
heatsink. Although better, a single IRFP460 will also be inadequate. You
will likely need to use at least three IRFP460 devices in parallel all
mounted to a single or three separate heat sinks. I'll provide the link to
the IRFP460P datasheet again for reference:

http://www.irf.com/product-info/datasheets/data/irfp460p.pdf

We notice from figure 11 in the datasheet (transient thermal impedance
curves) that for a two second event we will receive no benefit from the
thermal inertia of the IRFP460 die. Therefore we will need to parallel
enough IRFP460 devices such that they could handle 40A of current
indefinitely (provided they had enough heatsinking).

So lets assume we use three IRFP460P devices in parallel for your solution.
How big should the heat sink be?

First find the steady state dissipation at 5A. I^2 * R at 25 deg. C with
three devices in parallel will be around 2.25 Watts. Each of the three
devices would therefore be dissipating around 750mW of heat. Giving this is
a fairly small number, and we will need a heatsink anyway (for it's thermal
inertia), we will make the approximate assumption that the MOSFET dies will
be operating at say 50 deg. C prior to an overcurrent event. This is a
fairly arbitrary assumption, but it gives us a starting point to work with.

We will therefore also assume the heatsink temperature is around 50 deg. C
prior to an overcurrent event. Since the ultimate objective of these
calculations it to insure a design that will keep the MOSFET die
temperatures at or below 150 deg. C (their rated maximum), we will need to
know the thermal resistance of the MOSFET dies to heat sink. From the
IRFP460P datasheet the thermal resistance should be (without electrically
isolating thermal pad, but with a flat heatsink that has been greased and
appropriately torqued) around 0.45 + 0.24 deg. C/W = ~0.7 deg. C/W.

So now how much heat must the MOSFETs dissipate at the end of the 40A
overcurrent event? Let us assume we allow them to reach the maximum die
temperature allowed (150 deg. C) after two seconds. This means their on
resistance will be around 0.27*2.5 (from figure 4) = 0.675 Ohms. For three
in parallel the total MOSFET set resistance is 0.225 Ohms. So I^2 * R at
40A and 150 deg. C is 360W. Each device must dissipate one third of this or
120W.

Now we can approximate the thermal rise due to the thermal resistance
between die and heatsink. 120W * (0.7 deg. C/W) = 84 deg. C. So 150 deg.
C - 84 deg. C = 66 deg. C. Since we assumed the heatsink would start at a
temperature of 50 deg. C (mainly due to ambient heat), this means we have
66 - 50 = 16 deg. C heatsink temperature rise to work with. So we need to
select a heatsink with enough thermal mass so as not to rise more than 16
deg. C given our anticipated total energy lost during the overcurrent event.

During the overcurrent event we assumed the MOSFET set is dissipating 360W
(given a die temperature of 150 deg. C, which is probably fairly accurate
since the MOSFET dies will heat up to near 150 deg. C very quickly compared
to the two second event since most of the thermal rise will occur between
die and heatsink). Since the overcurrent event can last up to two seconds,
the total energy dissipated should be no more than about 360 W * 2 s = 720
Joules. So we need a heat sink capable of taking 720 Joules with only a 16
deg. C temperature rise.

Assume we select aluminum as our heatsink material. Aluminum has a specific
heat of 900 J/(kg*K). Solving for the heat sink mass (720 J) * (kg*K/900 J)
* (1/16 K) = 0.05 kg. Since aluminum has a density of 2700 kg/m^3, we need
a heatsink that has a volume of at least 18.5 cm^3 and mass of 0.05kg. You
could use either one heatsink of 18.5 cm^3 or three heatsinks of 6.2 cm^3.
The optimal heatsink shape in this case would not have large fins, but be
one large rectangular block, since a solid block would have less thermal
resistance between the TO-247 contact point and the rest of its thermal
mass.

The heat sink/spreader does not need to dissipate much steady state heat, so
you could pot the whole heatsink or cover it with something electrically
insulating if desired to increase technician safety (and/or comply with
possible safety organization specifications). Unfortunately when using only
three IRFP460P devices you will not be able to use electrically isolating
thermal pads (unless they are extremely good) since they will increase the
thermal resistance from package to heatsink too much. SOT-227 packaged
devices are usually extremely expensive, but it does have the very novel
feature that you get an electrically isolated heat sink tab.

So does this help answer your questions?
 
F

Fritz Schlunder

Jan 1, 1970
0
Hmm... The TO-247 package has a mass around 6 grams. If we assume the
package has a specific heat around that of copper of 385 J/(kg*K), then by
my calculations you should be able to safely handle the overcurrent
condition if you simply parallel five or more IRFP460P devices with no heat
sink necessary. Someone want to double check me?

I recommend you use this strategy. Digikey sells the IRFP460P device in ten
unit quantities for US $1.386 each. So a full solution of five IRFP460P
devices with no heat sinks (or heat sink grease, screws, safety issues of
"live" heatsink, mounting torque reliability problems, etc.) would only cost
$6.93 if they were purchased in ten unit quantities from Digikey.

Oh yeah, make sure to read this first:

http://www.irf.com/technical-info/appnotes/an-941.pdf

Try to keep the parasitic components well balanced across all devices, and
use separate gate drive resistors.
 
E

Electronic Swear

Jan 1, 1970
0
If I go to use 3-5 pieces of IRFP460, I cannot afford that high
costing as I just want to complete it within US$1-2.

Is there any cheaper method to do the same job?
Of course, there are some IGBTs can handle high current rating.
However, the cost is still very expensive.

May I know that any mechanical device can do as a switch to avoid
over current?
 
W

Winfield Hill

Jan 1, 1970
0
Electronic Swear wrote...
If I go to use 3-5 pieces of IRFP460, I cannot afford that
high costing as I just want to complete it within US$1-2.

Is this is a mass-production design? Thousand-piece quantities
or higher? How much are you paying for the motor?
Of course, there are some IGBTs can handle high current rating.
However, the cost is still very expensive.

I may have misled you by mentioning Fairchild's very capable
HGT1N40N60A4D 600V 40 IGBT. Smaller low-cost parts can handle
40A for a few seconds, with a suitable heatsink. For example
a Fairchild HGTG20N60B3 costs about $2 each qty 1k. It drops
under 1.5V at 5A, dissipating less than 7.5 watts.

You start by keeping the case temp down with a moderate-sized
heat sink. This allows the IGBT junction to increase by 75 to
125C during a short 40A event, as the heat spreads to the tab
and some adjacent aluminum. The HGTG20N60 will drop about 2.3V
at 40A at the beginning (junction at 40C), which is 92 watts,
increasing to about 2.8V (112 watts) as the junction heats up.
This is well within the rating of the IGBT (165 watts 25C case)
if you directly bolt on a slab of aluminum with a small amount
of grease but _without_ an insulator, before some insulation to
the rest of your finned heatsink.

I assume you're making the on/off signals? You'll have to be
sure to shutoff the IGBT after only 2 to 3 seconds at 40A.

Tell us some detail about what you're working on.
Is there any cheaper method to do the same job?

If you're rectifying 220 AC for your DC motor, you can use two
triacs in the bridge, in place of diodes, each conducting 5A (or
40A) for every other half cycle. Low-cost TO-220 commodity 25A
triacs can conservatively handle the task with a modest heatsink.
You'll need gate triggers each half cycle, or a continuous drive.

For example, Philips' BTA225-600B costs $0.75 qty 500 at Future,
ST's BTB08-600B is $1.15 qty 1.5k at Future, Teccor Littlefuse's
Q6025L6 is $1.69 qty 1k at DigiKey. Some types have insulated
tabs, but you'd have to examine their thermal-resistance ratings.
 
E

Electronic Swear

Jan 1, 1970
0
Thank you for your opinion.

Basically, I am doing over current protection when the motor is going
to lock rotor. I am not monitoring the current but monitoring the speed
of the motor. I use the power Mosfet /IGBT to be a switch for cut-off.

Of course, in normal operation, motor is running and the transistor need
to handle 5-6A current. However, if there are rotor locking, the current
will rise to 40A. When circuit detect the speed is zero, it will trigger
the transistor to cut-off.

I am quite interested on using triac to cut-off. However, I still not
catch your point on where to place the triac on the bridge recifier side.
Can you give me a more clear schematic on it?

Thanks~
 
W

Winfield Hill

Jan 1, 1970
0
Electronic Swear wrote...
Basically, I am doing over current protection when the motor is going
to lock rotor. I am not monitoring the current but monitoring the speed
of the motor. I use the power Mosfet /IGBT to be a switch for cut-off.

Of course, in normal operation, motor is running and the transistor need
to handle 5-6A current. However, if there are rotor locking, the current
will rise to 40A. When circuit detect the speed is zero, it will trigger
the transistor to cut-off.

I am quite interested on using triac to cut-off. However, I still not
catch your point on where to place the triac on the bridge recifier side.
Can you give me a more clear schematic on it?

Winfield Hill wrote ...

Any answers for us here?

[Well, I guess you can see how top-posting messes up a conversation.]

I haven't used this configuration myself, but I've seen others do it.
Here's the basic idea:

.. H ----------------,
.. SCR1 |
.. ,--A-|>|-K--o--o----|>|---,
.. | \ G | D1 |
.. | '--xx--' |
.. N ----| -------, |
.. | SCR2 | D2 |
.. o---|>|--o-----o----|>|---+--o-----------,
.. | \ | | snubber |
.. | '--xx--' _|_ cap DC +
.. | SCR gate --- MOTOR
.. | transformers | | -
.. '----------------------------o-----------'

You are using unfiltered rectified AC for your DC motor, right? If
you want to use this scheme with large DC filter capacitors, series
inductance must be added. In any event, snubber caps are needed.

I was mistaken, SCRs are used instead of triacs. This saves a few
pennies, an MCR25M costs $1.31 qty 10 at DigiKey, and $0.71 qty 1k.

If you use delayed-phase switching, you can control the motor power.

You can also switch on the high side of the dc output line,

.. AC line _____
.. H --------------, G-------| |
.. | |/ | direct
.. ,---|>|---o---A-|>|-K--, | gate
.. | D1 SCR1 | | control
.. | ,--|----|_____|
.. | D2 |/ | |
.. o---|>|---o-----|>|----o---o---o----,
.. | | SCR2 _|_ | +
.. N ----|---------' --- MOTOR
.. | snubber | | -
.. '--------------------------o--------'

Either form is similar using gate trigger transformers, but high-side
switching allows you to use convenient direct gate-drive connections.
However, this requires the control circuits to ride on the high-side
of the switched voltage, which can be VERY DANGEROUS during testing.

In testing direct ac control it's required that you NEVER connect your
scope ground to the logic ground, etc., and you must take exceptional
safety precautions. It's required for Hot switching, but if you use
a form of Neutral line switching, you should still absolutely _not_
count on the ac line being properly wired.

Perhaps others who have more experience with 1 HP motors will comment
further about SCR motor control.
 
N

Nico Coesel

Jan 1, 1970
0
Thank you for your opinion.

Basically, I am doing over current protection when the motor is going
to lock rotor. I am not monitoring the current but monitoring the speed
of the motor. I use the power Mosfet /IGBT to be a switch for cut-off.

Of course, in normal operation, motor is running and the transistor need
to handle 5-6A current. However, if there are rotor locking, the current
will rise to 40A. When circuit detect the speed is zero, it will trigger
the transistor to cut-off.

I think this is not very reliable, because you assume the motor will
be running at a certain speed in a few seconds after switching it on.
Why not use a small series resistor and sense the current? If it goes
over a specific current, you shut the circuit down or turn the
transistor off for 1 AC cycle. The latter also provides a crude
soft-start mechanism.
Also, you might be able to get away with 1 FET or IGBT because you can
determine the current handling limits of the transistor more
precisely.
 
W

Winfield Hill

Jan 1, 1970
0
Nico Coesel wrote...
I think this is not very reliable, because you assume the motor will
be running at a certain speed in a few seconds after switching it on.
Why not use a small series resistor and sense the current? If it goes
over a specific current, you shut the circuit down or turn the
transistor off for 1 AC cycle. The latter also provides a crude
soft-start mechanism.
Also, you might be able to get away with 1 FET or IGBT because you
can determine the current handling limits of the transistor more
precisely.

This is correct, because allowing the condition to exist for several
seconds forces one to use 40 to 50A parts, or a pair of 25A parts.
On the other hand, if the over-current condition was limited to say
6 cycles, or 0.1 sec, a single low-cost 10 to 12A IGBT could be used.
The savings would more than compensate for the added power resistor.
 
W

Winfield Hill

Jan 1, 1970
0
Winfield Hill wrote...
Electronic Swear wrote...
Basically, I am doing over current protection when the motor is going
to lock rotor. I am not monitoring the current but monitoring the speed
of the motor. I use the power Mosfet /IGBT to be a switch for cut-off.

Of course, in normal operation, motor is running and the transistor need
to handle 5-6A current. However, if there are rotor locking, the current
will rise to 40A. When circuit detect the speed is zero, it will trigger
the transistor to cut-off.

I am quite interested on using triac to cut-off. However, I still not
catch your point on where to place the triac on the bridge recifier side.
Can you give me a more clear schematic on it?

[Well, I guess you can see how top-posting messes up a conversation.]

I haven't used this configuration myself, but I've seen others do it.
Here's the basic idea: [ snip ]

You are using unfiltered rectified AC for your DC motor, right? If
you want to use this scheme with large DC filter capacitors, series
inductance must be added. In any event, snubber caps are needed.

I was mistaken, SCRs are used instead of triacs. This saves a few
pennies, an MCR25M costs $1.31 qty 10 at DigiKey, and $0.71 qty 1k.

If you use delayed-phase switching, you can control the motor power.

You can also switch on the high side of the dc output line,

. AC line _____
. H --------------, G-------| |
. | |/ | direct
. ,---|>|---o---A-|>|-K--, | gate
. | D1 SCR1 | | control
. | ,--|----|_____|
. | D2 |/ | |
. o---|>|---o-----|>|----o---o---o----,
. | | SCR2 _|_ | +
. N ----|---------' --- MOTOR
. | snubber | | -
. '--------------------------o--------'

Either form is similar using gate trigger transformers, but high-side
switching allows you to use convenient direct gate-drive connections.
However, this requires the control circuits to ride on the high-side
of the switched voltage, which can be VERY DANGEROUS during testing.

In testing direct ac control it's required that you NEVER connect your
scope ground to the logic ground, etc., and you must take exceptional
safety precautions. It's required for Hot switching, but if you use
a form of Neutral line switching, you should still absolutely _not_
count on the ac line being properly wired.

You could save money using lower-cost 8A jelly-bean SCRs, if you can
limit the overcurrent time to 0.1s or less, using a sense resistor.
You'd also benefit from a reduced heat-sink thermal-mass requirement.

.. AC line _________
.. H --------------, G------| |
.. | |/ | direct | with overcurrent
.. ,---|>|---o---A-|>|-K--, | gate | sense resistor
.. | D1 SCR1 | | control | for stalled motor
.. | ,--|---|_________| shutdown
.. | D2 |/ | | |
.. o---|>|---o-----|>|----o-----o-/\/-o--o--------,
.. | | SCR2 sense _|_ | +
.. N ----|---------' --- MOTOR
.. | snubber | | -
.. '-------------------------------------o--------'
 
R

Rich Grise

Jan 1, 1970
0
Winfield Hill wrote... ....
....

You could save money using lower-cost 8A jelly-bean SCRs, if you can
limit the overcurrent time to 0.1s or less, using a sense resistor.
You'd also benefit from a reduced heat-sink thermal-mass requirement.

. AC line _________
. H --------------, G------| |
. | |/ | direct | with overcurrent
. ,---|>|---o---A-|>|-K--, | gate | sense resistor
. | D1 SCR1 | | control | for stalled motor
. | ,--|---|_________| shutdown
. | D2 |/ | | |
. o---|>|---o-----|>|----o-----o-/\/-o--o--------,
. | | SCR2 sense _|_ | +
. N ----|---------' --- MOTOR
. | snubber | | -
. '-------------------------------------o--------'

And here, I was going to say, "How about a 10A slow-blow fuse?"

Or is this rotor-locking condition a regular occurrence, in which case it
should be written into the control algorithm?

Thanks,
Rich
 
R

Rich Grise

Jan 1, 1970
0
Nico Coesel wrote... ....
This is correct, because allowing the condition to exist for several
seconds forces one to use 40 to 50A parts, or a pair of 25A parts.
On the other hand, if the over-current condition was limited to say
6 cycles, or 0.1 sec, a single low-cost 10 to 12A IGBT could be used.
The savings would more than compensate for the added power resistor.

I think the guy's overreacting. How big can a 5A motor be? Did he say
how many volts? At 120, a 5A is a modest vacuum cleaner motor. What kind
of process is he controlling that a vacuum cleaner motor routinely stalls?
And what is it about that stage of the process such that the stall occurs
at that time? Figure out what you're trying to accomplish, and design the
process around that.

If it stalls unpredictably at random times, then obviously the motor is
undersized for the application, and he's trying to apply band-aids to
cover up the fact that they don't like to replace the fuse every time they
forget to clear the pinch roller.

Good Luck!
Rich
 
E

Electronic Swear

Jan 1, 1970
0
The DC motor is operated at (rectified) 220Vac.
It is for food juicer. We don't want to use current
sensing because the motor start-up current is very large.
Similiar to what the current at lock rotor. As a result,
current monitoring is not a very good method. Even the motor
will be over-loading for a short moment when the user is putting
a very hard / big food for juicing at the beginning.
The current will be very large at the beginning but will drop
to a suitable value. However, we cannot cut-off the motor source
because of over-current. We will allow the motor operating at a
very high current for a short time, several seconds.

The motor is for masss production and look for safety protection
as well. If use fuse on protection, it is very inconvenient for
exchange. We want some active protection rather than passive components.

I will try for using the SCRs at the bridge rectifying.
However, the current rating of the SCR just 25A is enough or not?
And any detail on snubber capacitor?
 
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