Which MOSFET / IGBT can afford 5A current normal operation a

[Electronic Swear]

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.

 

[Winfield Hill]

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.


--
Thanks,
- Win

 

[Tony Williams]

In article <co3hpd06tq@drn.newsguy.com>,
Winfield Hill <hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote:

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.

--
Tony Williams.

 

[Electronic Swear]

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?









"Fritz Schlunder" <me@privacy.net> wrote in message news:<30mqr0F321ahfU1@uni-berlin.de>...

"Fritz Schlunder" <me@privacy.net> wrote in message
news:30mkf5F327n2aU1@uni-berlin.de...

"Electronic Swear" <swear_terence@hotmail.com> wrote in message
news:910532f6.0411241718.75622eea@posting.google.com...
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?



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.

 

[Winfield Hill]

Winfield Hill wrote...

In any event, snubber caps are needed.

http://www.onsemi.com/pub/Collateral/AN1048-D.PDF


--
Thanks,
- Win

 

[Winfield Hill]

Fritz Schlunder wrote...

If this is a consumer product I should imagine if you let the
motor draw 40A for two seconds in a lot of instances it will
trip the household circuit breaker...

Perhaps it isn't at 40A for the entire 2 seconds... Or...
Hmm, if the machine is straining, wihch the user can tell,
I think 2 seconds is a rather long time... Try it out.


--
Thanks,
- Win

 

[Electronic Swear]

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?














nico@puntnl.niks (Nico Coesel) wrote in message news:<41a8862e.308874387@news.planet.nl>...

swear_terence@hotmail.com (Electronic Swear) wrote:

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.