12 channel injector module - VNS14NV04

[AndreyB]

This board is an older brother of 6 channel injector module

[AndreyB]

Q: what is we change to 'open drain' pin output? This would give us 5v on the MOSFET control pin.
A: this would raise the issue that the default would be ON, so we will get injectors open while the MCU is starting

[AndreyB]

@ is suggesting different MOSFETs because these are much cheaper and much more available in RU
Injector configuration: IRF7470 + TVS diode P6KE30A (0.9$ + 0.25$ in RU)
Solenoid configuration: IRF7413Z + SF22 (0.33$ + 0.10$ in RU)
Relay configuration: just IRF7413Z

I believe this requires a diode to +12 in addition to exiting GND diode. I am asking the Russians to adjust the board accordingly but you know these Russians...

[kb1gtt]

This board had some vias where a diode can be added. I'm a bit concerned about it thermally but haven't checked to see if it's an issue or not. If the MOSFET fits the pads, and the diode fits, it's easy enough to try it out and see what happens.

[kb1gtt]

I expect the inductive energy absorbed by a 40V OVP MOSFET (or zener style diode) to be about 3watts perhaps as much as 5 watts per channel. From my analysis found here http://code.google.com/p/daecu/wiki/Injector_driver_theory I got the snippet below. (sorry it's still poorly wirtten)

Lets look at this another way to double check that the decay seems about right. From here http://en.wikipedia.org/wiki/Inductor#Stored_energy we get .5(.035H)(1A^2)= .0175j. Then from here http://en.wikipedia.org/wiki/Watt#Definition and assuming we dissipate at a constant 20 watts, the decay time would be .0175j / 20W = .0008S. Which is about what I expected and see in the simulation.

At 9kRPM that would mean if the injectors are injecting on a per rev basis, it would rotate/pulse 150 times in 1 second. So it would be in OVP decay for 150cycle/second x .001seconds/cycle=.15 seconds per one second of rotation. So 15% of the OVP heat is dissipated on average. 15% of 20W is about 3 watts total heat caused by the OVP MOSFET decay per injector channel.

I measured that 35uH injector from a reasonably small injector. Other injectors may have more uH which would cause more energy dissipated in the OVP diode. The datasheet for the P6KE30A notes a min of 20C/W from junction to leads. I don't know the resistance from the leads to ambient. I'd guess 50C/W to 100C/W is in the ball park. I'll assume 50C/W. Which means the 3W's dissipated will raise the temperature by 150C. This can be a problem for the ambient temperature as the diode junction needs to stay under 150C. I think the diode needs to have a better thermal path to the heat sink. Either that or less energy to be absorbed.

I like the IRF7413Z, it's a 30V OVP MOSFET, with good switching times and it has the same pin out as the chips we have been using. This chip claims it can handle 32mJ, and as noted above and in my analysis some time ago, the injector I measured was 17.5mJ. I wonder why they don't advertise it as automotive. Perhaps they simply didn't follow some automotive standard. I know many automotive grade parts have testing that ensures a 0% failure rate. As far as I can tell from the datasheet, it holds all the critical physical specs required. All that for $0.44 in qty 1, how can you beat it?

[AndreyB]

From http://open5xxxecu.org/viewtopic.php?f=44&t=72&p=892#p892

[kb1gtt]

Cool and good to hear it's being used for a flow bench.

[AndreyB]

I like the IRF7413Z, it's a 30V OVP MOSFET, with good switching times and it has the same pin out as the chips we have been using. This chip claims it can handle 32mJ, and as noted above and in my analysis some time ago, the injector I measured was 17.5mJ. I wonder why they don't advertise it as automotive. Perhaps they simply didn't follow some automotive standard. I know many automotive grade parts have testing that ensures a 0% failure rate. As far as I can tell from the datasheet, it holds all the critical physical specs required. All that for $0.44 in qty 1, how can you beat it?

Would IRF7413Z require a diode for injector control?

Would IRF7413Z require a diode for relay control?

[kb1gtt]

IRF7413Z may need some protection on the gate as ripple might go upstream to the STM32. However the STM32's rail clamping diodes are probably good enough for this. Small unknown, but it's probably OK with out added diodes for relay or injectors.

[AndreyB]

Sounds like I should take one of the older boards and modify it to use IRF7413Z

[AndreyB]

VNS14NV04PTR-E not in stock anywhere anymore? I am not sure if they are replacing it with some other part or if it has simply fallen out of favor?

[AndreyB]

How acceptable would VNS3NV04PTR-E be? http://www.st.com/resource/en/datasheet/vnn3nv04p-e.pdf
Rds=120 mΩ
lim=3.5 A

[Rhinoman]

I have doubts about the choice of these FETs, the protection circuit cutting in is going to lift the gate voltage, the datasheet states 8V maximum. The drive voltage is labelled at 5V but as far as I can see its a 3V drive direct from the micro through a 20R resistor which gives (8-3)/20 = 250mA. It seems like the FET is protected but the micro isn't; even in normal use if its avalanching then it could be spiking the micro. I'm not at home so I can't test that, I don't see anything in the datasheet that says that it disconnects the gate except during over temperature shut down.

[nagyOUT]

From http://open5xxxecu.org/viewtopic.php?f=44&t=72&p=892#p892

Wow blast from the past! Glad to see you found my photos from that other forum

We didn't end up using this as the controller for the flow bench due to doing alot more low imp injectors than high imp.. Just ended up using an Haltech for the task.