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Topic: Alternative to a MOSFET ? (Read 2514 times) previous topic - next topic

Gadget999

I am using this mosfet to PWM a 12V motor

IRF540 - http://www.maplin.co.uk/mos-fets-33843?ordercode=N10AH

it is mounted on a heat sink - and i am getting it HOT

hot enough to melt the solder !

i need something with a higher current rating

any suggestions ?

do i need to use an IGBT ?

James C4S

It isn't possible to recommend anything with only knowing the voltage rating of the load.  You need to tell us what the characteristics of your motor are in order to answer the question.  
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

Gadget999

#2
Jul 29, 2011, 04:08 pm Last Edit: Jul 29, 2011, 04:15 pm by Gadget999 Reason: 1
hi guys

The motor is being switched from a 12v car battery
the heatsink is only slightly larger than the mosfet (supplied by maplins)
the motor is from an electric battery drill - i do not know its spec
the arduino is providing the pwm

the current the motor pulls i guess is down to how hard it is working

can you take a look at this mosfet - http://www.irf.com/product-info/datasheets/data/irl2203n.pdf

rated at 116 Amps at 10V or 400 Amps pulsed !!

is this one any good ? - http://www.ebay.co.uk/itm/New-1pcs-G80N60RUFD-G80N60-80N60-80A-600V-TO-3P-IGBT-/190508662045?pt=LH_DefaultDomain_0&hash=item2c5b337d1d

MarkT

#3
Jul 29, 2011, 04:54 pm Last Edit: Jul 29, 2011, 04:57 pm by MarkT Reason: 1
The IRF540 is not logic-level, its not suitable for driving from 5V as it won't be fully on. Logic level MOSFETs have Ron characterised at Vgs=4.5V, not 10V. The vast majority of TO220 GETs are _not_ logic-level, note
[ I won't respond to messages, use the forum please ]

Erni



An example of a logic level MOSFET could be RFP30N06

http://www.sparkfun.com/datasheets/Components/General/RFP30N06LE.pdf

See sparkfun

http://www.sparkfun.com/products/10213

Gadget999

Thanks for the advice. So i need a logic level mosfet that is fully on at 5v. I am thinking i may go for one with a higher current rating to be safe. Are any of the ones I posted earlier suitable?

CrossRoads

Or try installing a driver before the MOSFET so that its Gate can switch fully on & off.
Say an NPN transistor driven by arduino thru a base resistor. Collector pulled high with 10K resister, connected to the gate.
Emitter to ground.  When NPN base is High, MOSFET will be turned off, and NPN base is low, MOSFET will be turned on.
Maybe use 2 so that PWM signal is not inverted.
Or use an open collector logic gate, like 7406, to do the same.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

JetIgniter2k

Quote
the heat sink is only slightly larger than the mosfet (supplied by maplins)


Much bigger!! if it's getting that hot.

http://www.changpuak.ch/electronics/calc_23.php

Determine how many watts you need to dissipate, and it will tell you what size heat sink you need.  Then you can go to newark or digikey to see what will work, the smaller the value the bigger the heat sink.  You can get away with a smaller one if you cool it with a fan. 

Grumpy_Mike

Quote
I am thinking i may go for one with a higher current rating to be safe.

More current rating will not make it any safer, it is the on resistance that together with the current determines the heat generated in the FET.

That FET is fine if you turn it on with a voltage in excess of 10V. The 12V supply you have is a good voltage to pull up to, with a transistor pulling it down to turn it off and protecting the arduino. Just like CrossRoads said.

CrossRoads

Non-inverting motor drive with 2 NPNs and N-Channel MOSFET
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

MarkT

In general the specified current for a MOSFET is the current at which it will be running at full power with large heatsink.  Ignore the current rating and calculate the power dissipation from I-squared-R.  In general you won't be taking the device to anything like its 'current rating'.  A 0.01ohm 170A MOSFET is good for 5 to 10A for instance - unless you bolt it to a water-cooled 200W heatsink - in which case you might get 100A through it OK.

For high current _pulses_ however the current rating is very useful - you need to know the bonding wires won't melt.
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