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injectors - [56k beware page 2] 
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LQFP112 - Up with the play
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That depends, do you want something you can buy now..or something you have to buy in bulk??

I think the ones I was looking at the other day were made by ST - part number VND5N07 or something like that. TO 251, 70V clamp, 5A limited. I'de prefer the same but 40V clamp, which I think they produce in a TO-251 also, but if memory serves digikey either didn't have them, or you had to order them in batches of like 3000. hahha, no way. Even the 70V ones you have to order 50 I think, but at about $1 each I'm not too fussed about having to order that many.


Wed Jul 30, 2008 12:10 pm
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0.1 ohm is far too high anyway. And that's assuming you want to use one. The only really valid point for using one is current limiting and that is taken care of internally.

If you did want to use one, a 0.01 ohm 2 watt resistor would be suitable.

The FETs with higher current rating typically have lower RDS and thus dissipate less heat and waste less injector turning on energy. That probably means faster turn on (by some immeasurable amount) assuming the switching characteristics are comparable and all else is equal.

The reasons for going higher (5 is the min practical anyway) are :

Drive heavy accessory loads with the same parts
Have head room under normal conditions
Stay out of current limiting during switch on/off to ensure fast consistent opening

I bought a bunch (30, though i could have bought 1), though the circuit should be tolerant of using a 5amp or 20 amp variant IMO. vnp5n07 is pin out compatible as is vnp20n07 and many many others.

Fred.

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Wed Jul 30, 2008 12:19 pm
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LQFP112 - Up with the play
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Fred wrote:
0.1 ohm is far too high anyway. And that's assuming you want to use one. The only really valid point for using one is current limiting and that is taken care of internally.

If you did want to use one, a 0.01 ohm 2 watt resistor would be suitable.

The FETs with higher current rating typically have lower RDS and thus dissipate less heat and waste less injector turning on energy. That probably means faster turn on (by some immeasurable amount) assuming the switching characteristics are comparable and all else is equal.

The reasons for going higher (5 is the min practical anyway) are :

Drive heavy accessory loads with the same parts
Have head room under normal conditions
Stay out of current limiting during switch on/off to ensure fast consistent opening

I bought a bunch (30, though i could have bought 1), though the circuit should be tolerant of using a 5amp or 20 amp variant IMO. vnp5n07 is pin out compatible as is vnp20n07 and many many others.

Fred.


Resistors on the low side of the FET are also used for current sense - not necessary at all with injectors if you don't want and we've had that discussion. However if you were using them for Solenoid control and trying to set a constant current through the solenoid you would need it - eg transmission control.

4A is all you need for peak and hold low Z injectors. 5A would be better. Nothing I can think of would need more than that (I'm sure someone else will think of something so upon further thinking its probably a good thing anyway.)

Switching characteristics generally have nothing to do with bulk design (what affects Rds ON) and have everything to do with gate design (input capacitance).

I think what will make this project most versatile is that you can use what ever hardware you like. I myself would like to see the driver boards being modular, that way if you want say gearbox control you add the board, if you want LPLPG you can design a board that peaks at 30V 10A and holds at 12V 1A etc etc. Inputs can be changed too if you look at it that way, ie sensor boards could also be modular...with core sensors being standard on the main board and core outputs say 4 ign 4 inj being standard or what ever.


Wed Jul 30, 2008 2:36 pm
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Delta wrote:
4A is all you need for peak and hold low Z injectors. 5A would be better. Nothing I can think of would need more than that (I'm sure someone else will think of something so upon further thinking its probably a good thing anyway.)
Radiator fan control for one :-)
Quote:
Switching characteristics generally have nothing to do with bulk design (what affects Rds ON) and have everything to do with gate design (input capacitance).
Understood, the gate capacitance and current fed to it control the switching time of the FET, but the RDS has some effect (even if small) on the switching time of the injector by allowing more voltage (and therefore current) to make it to the injectors.
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I think what will make this project most versatile is that you can use what ever hardware you like.
Absolutely, but what we need to get the project off the ground is a basic solid setup that works for most people in a simple bare bones kinda way. Hence not keen on current sensing outside the fet and not keen on pwm thermistors and not keen on hall sensed injector outputs and even not keen on on board IGBTs for ignition, though the pads for any of them could be present as I don't have to populate it.

For other stuff I'd like to see jumperable (by solder/wire) connections for pull down, pull up 5v/12v on all GP I/O channels that we configure. We want to avoid jumper wires running around the boards like ms installations always/often have. We want to avoid prototyping area being used for normal stuff. etc.

Once the project has grown wings, there will be enough human resources to generate all kinds of different hardware for the code to run on :-)

Fred.

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Wed Jul 30, 2008 4:08 pm
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