This page describes different varieties of FETs (e.g. logic-level, DPAK) used by the VEMS group. It is primarily intended for use by developers.
Vanilla FET -- TO220
Used as cheap/easy to find switching drivers for injectors. Low RDSon requires the use of a FET driver:
non-isolated (forget them)
Logic-Level FETs -- TO220
|FQPF20N06L||15A, 9.5nC, Rds=0.055 logiclevel. Available in the Web Shop. The recommended insulated logic-level FET for the injector drivers and WBO2 heater driver.||http://www.fulcrum.ru/Read/CDROMs/FAIRCHILD/DISK3/PDFs/MOSFETs/TO-220F/N-Channel/FQPF20N06L.pdf|
|IRLI 530 N||(Lomex appr. 1Euro, 50pcs, 2 weeks) logiclevel 30V/116A (130W)|
|IRL2505||50V/10A/logic level FET/TO220|
|IRLIZ24N||TO220 Fullpack (Isolated) vclamp 55v, Rds ON 105mOhm (4.5v Vgs),Rds ON 60mOhm (10v Vgs) Ids 9.9A @ 100C, Total Gate charge= 15nC. Rth Junction to case= 4.8C/W, Rth Junction to ambient 65C/W. Power dissipation 26W.|
|IRLIZ34N||TO220 Fullpack (Isolated) vclamp 55v, Rds ON 60mOhm (4.5v Vgs),Rds ON 35mOhm (10v Vgs) Ids 14A @ 100C, Total Gate charge= 25nC. Rth Junction to case= 4.1C/W, Rth Junction to ambient 65C/W. Power dissipation 31W.|
|IRLIZ44N||TO220 Fullpack (Isolated) vclamp 55v, Rds ON 35mOhm (4.5v Vgs),Rds ON 22mOhm (10v Vgs) Ids 20A @ 100C, Total Gate charge= 48nC. Rth Junction to case= 3.3C/W, Rth Junction to ambient 65C/W. Power dissipation 38W.|
|IRLI2505N||TO220 Fullpack (Isolated) vclamp 55v, Rds ON 13mOhm (4.5v Vgs),Rds ON 8mOhm (10v Vgs) Ids 41A @ 100C, Total Gate charge= 130nC. Rth Junction to case= 2.4C/W, Rth Junction to ambient 65C/W. Power dissipation 63W.||http://ec.irf.com/v6/en/US/adirect/ir?cmd=catProductDetailFrame&productID=IRLI2505|
Note: most of the above are available as SMDs (e.g. TO-252 aka DPAK).
|RFD16N05LSM||16A, 50V, 0.047 Ohm, Logic Level, N-Channel Power MOSFETs DPAK||http://www.fairchildsemi.com/pf/RF/RFD16N05LSM.html|
|HUF76121D3S||Commercial 30 V 20 A 23 mOhm 13 nC 4.5v compatible DPAK|
|HUF76419D3S||Commercial 60 V 20 A 37 mOhm 23 nC 4.5v compatible DPAK|
|HUF76423D3S||Commercial 60 V 20 A 32 mOhm 28 nC 4.5v compatible DPAK|
|HUF76429D3S||Commercial 60 V 20 A 23 mOhm 38 nC 4.5v compatible DPAK|
|HUFA76413D3S||AutoCommercial? 60 V 20 A 49 mOhm 17 nC 4.5v compatible DPAK|
|HUFA76419D3S||AutoCommercial? 60 V 20 A 37 mOhm 23 nC 4.5v compatible DPAK|
|HUFA76423D3S||AutoCommercial? 60 V 20 A 32 mOhm 28 nC 4.5v compatible DPAK|
|HUFA76429D3S||AutoCommercial? 60 V 20 A 23 mOhm 38 nC 4.5v compatible DPAK|
|ISL9N327AD3ST||Commercial 30 V 20 A 27 mOhm 17nC 4.5v compatible DPAK|
Most frequently used (stocked in high quantity) products marked bold. IRLR024N is the mass FET, and HUFA76423D3S where very high current is needed, eg. switching supply for CdiSupply and IonSense. All DPAK of course
These FETs have added protection like:
- Drain to Source clamp when voltage is over a set value.
- Overcurrent protection, usuallly clamped shutdown for low side switches.
- Over Temperature protection through shutdown.
- Smart FET's usually have higher Rds ON compared to vanilla or logic level fets.
|IPS021||150mOhm, Ishutdown 5A, Tshutdown 175C, Vclamp 50v, 3.3nC Total gate charge.||http://www.irf.com/product-info/datasheets/data/ips021.pdf|
|IPS031||60mOhm, Ishutdown 12A, Tshutdown 175C, Vclamp 50v, 11nC Total gate charge. My preferred injection and misc driver (Jörgen).||http://www.irf.com/product-info/datasheets/data/ips031.pdf|
Multiple FETs In One Package
|TPIC6A259||8 * 350 mA (used on v3.x)|
|MC33291||8 * 500 mA (uses SPI, more complex than 259)|
|ULN....||unipolar stepper drivers|
|SN754410 (L293)||4* 1A push-pull like several other bipolar stepper drivers (used on v3.x)|
The FET driver is simple inverting device. If input is above threshold (appr. 2V), the output will be close to 0V, below that threshold output will be close to supply (+12V). The input is 0 or 5V with the AVR driving it. Anything between means PWMing is active.
For lowZ injectors, which switch upto about 16000 times a second if PWM-ing is configured, fast switching is needed to keep dissipation (heat) down.
The FETdrivers do exactly this:
- FETdrivers enable fast switching
- they enable the use of non-logic level FETs
- the MC34151D that's most common (see PWMing kit in WebShop) also inverts the signal (my_make must match this). In the future we'll prefer MC33151D (same footprint, small difference)
For highZ injectors, that only switch max 100 times a second FETdriver is not needed (but it works with installed FETdrivers).
Some scientific discussion on IRC (2004-03-04) about Smart FET vs. Generic FET
issue: lean-condition that can be created at serious errors with smart-switches (even though unlikely).
- <Jorgen> The choice between a vclamped FET with isolated case and a fully protected FET without isolated case isn't easy for me...
- <rich1> What is the worst case scenario for each?
- <Jorgen> Both are vclamped and can live without any other flyback. (not sure if the isolated part is built for it but it has the clamp). The isolated part will fail to a short circuit if there is an overcurrent / overtemperature condition. The Smart FET will just shut down if either happen.
- <rich1> A controlled shut down sounds like a nicer option to me...
- <Jorgen> The Smart fet can cause the injector duty to decrease if driven outside the limits. The other will flood the engine when it fails, or if it's a hard shortcircuit there will be damage to the board and cabling.
- <rich1> What is the downside of the Smart FET then? Higher cost?
- <Jorgen> By choosing the IPS31 smart fet the limits will be very far away from the operation range.
- <Jorgen> Very little difference.
- <rich1> Ok, I see now. So ideal is a smart fet with tighter limits
- <Jorgen> The current needed to charge the smart FET is also much smaller then what's needed for the other FET.
- <Jorgen> No, tight limits can cause problems for us.
- <Jorgen> Imagine that you run your setup with a few large injectors and you cause your injector FET to hit shutdown limit after 70% of the commanded duty. The injector shut's early and you loose the last 30% of fuel.
- <Jorgen> The next injector opening the same thing will happen.
- <rich1> Better a loss of power than frying them
- <rx7turbo> Would that be a big concern if the limit was far away from normal range though?
- <rich1> As long as there is some feedback of a problem, that should be bearable
- <Jorgen> No, if the limit is far away from the normal range it will not be a problem
- <Jorgen> You won't see loss of power, you will see a hole in your pistons...
- <rich1> So if the choice is burned motor vs burnt fet, i know what i'd choose...
- <rich1> Are there any fets with an overload signal as well?
- <Jorgen> We would need to add a diagnosis circuit on the board or switch to a high side switch with a diagnosis signal.
- <Jorgen> The Isolated switch with a fuse sounds good to me.
I suggest low-voltage FlyBack for injector drivers, using S2X (see below) SMB diodes and 0 Ohm 'resistors', or throughole diodes mounted SMD style with a bit art.