IGBT vs. MOSFET

Gentlemen,

I want to build an experimental test rig for controlling a 5 cylinder diesel engine. Obviously no ignition circuitry is required; it's just the fuel injector pulsing I need to worry about. The injector solenoids in question are very low DC resistance (~0.3 ohms!) and suck about 30A through current-limiting resistors when actuated. Now, the duty cycle is very, very small. A firing event only occurs every two revolutions (per cylinder) and typically lasts just a few milliseconds. The range of RPM is from 700 to 4000 in this case. So, which active device would make the best driver? This is strictly a one-off experiment so there are no production/cost considerations to worry about, BTW.

Reply to
Cursitor Doom
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Haven't done one of those, but I think the main issue is the voltage "kick" on turn-off... IIRC a "catcher" diode can't be used because it slows the turn-off. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

Yes, I have heard something like that, Jim. Could prove a PITA. :(

Reply to
Cursitor Doom

Solenoid driving can become mean. Once pulled in the inductance is higher :-( ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

Is it the diode capacitance that's the issue here? Would using a fast recovery diode for snubbing help at all? (I guess not or you would have said so).

Reply to
Cursitor Doom

The turn off time is limited by the reverse voltage. A catcher diode limits the reverse voltage to the supply voltage.

I've used active catching in relay-driver CMOS chips, mostly because on-chip diodes can't be used due to parasitic device action, but also because I can set the reverse voltage. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

This might be of use to me:

formatting link
solenoid-driving

I've not read it through yet as I have to go out now for a few hours, but will certainly examine it for tips later....

Reply to
Cursitor Doom

Good link. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

t

worse than that, a diode limits the reverse voltage across the solenoid to a diode voltage

common way to driver an injector is a low side mosfet with a zener/diode from drain to gate so the fet does the flyback clamping, you could use an a valanche rated fet but I guess the clamping as less defined

-Lasse

Reply to
Lasse Langwadt Christensen

My oopsy ;-)

That's the way my relay-driver chips work, except I don't use a zener, I do a reference loop to accurately set the clamp voltage. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

See...

NMOS_RelayDriver.pdf

and

RelayDriverClamped.pdf

on the S.E.D/Schematics page of my website. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

A diode will keep the solenoid current running (through the diode) when the switching element turns off. This is not a parasitic effect, it is the intended effect of the diode. But it delays the release of the solenoid.

Reply to
Rob

Putting the diode outside the current-limiting resistor loop will speed things up.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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Reply to
John Larkin

IGBTs make sense over 200 V, and they are slow. MOSFETs are great in the lower voltage range. You might need to accommodate 100V or more on the turn-off of the coil, depending on how fast the field needs to be collapsed. it might make sense to set up a PWM circuit rather than use current limiting resistors. A current sense resistor and a comparator could pulse the FET gate when the desired current is reached.

You will likely need a fast diode and a resistor to allow the controlled collapse of the magnetic field, while protecting the FET from excessive voltage.

I use the IRFB260N FET and the IR2110S and IR2181S gate drivers in some servo amps, they are reasonably fast (you can turn them on and off in 200 ns or so). It is a 56 A 200 V transistor, so should be quite good in your app.

Jon

Reply to
Jon Elson

Traditionally, SCRs are used for high current, low frequency switching. Because your load is inductive, the dI/dt limit is not going to be a problem. The high-speed-switch capabilities of a MOSFET would be wasted here, and bipolar transistors are very pricey if you want 30A peaks.

Something like 2N6395 would work (don't bother looking at the AVERAGE current rating, rather the 'repetitive peak' ).

Reply to
whit3rd

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ON for a few millisecond, how do you intend to do that with an scr?

-Lasse

Reply to
Lasse Langwadt Christensen

whit3rd magic ?>:-} ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

A TVS diode should be fast enough, though (transient voltage suppression). That would be the simplest solution IIRC.

Reply to
Gunther Heiko Hagen

Experiments with driving relays suggest that if the TVS clamping voltage is about 5 x the supply voltage the slowdown will be negligible.

John

Reply to
jrwalliker

IGBTs are used for ignition, because of the high voltage standoff required.

A solenoid will turn off acceptably quick with a (bidirectional) TVS or damping resistor across it. MOSFET all the way!

Tim

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Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
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Reply to
Tim Williams

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