> Date: Fri, 09 Oct 2015 23:08:27 -0400 > From: Neil >=20 > James, >=20 > I haven't measured, but inductance for these peak-and-hold injectors=20 > seem to be around 3mH to 5mH. >=20 > As far as I've found, PWM is a popular method for the hold phase -- once= =20 > the peak current has been reached, the hold phase is PWM'ed to get an=20 > average of the required hold current. IME, most ECU's use=20 > high-impedance injectors, so there's no hold phase. Is that possibly=20 > why you've not seen this? Or have you actually tinkered with ECU's that= =20 > drive P&H injectors? I'm curious to know what else they do for P&H=20 > injectors. >=20 > I am planning to measure the current dynamically, and I do have a=20 > 0.5-ohm sense resistor in place right now, and next up is handling the=20 > measurement/feedback part of the design, but I'm debating if a PIC A/D=20 > will be able to measure quickly enough, or if I should use a=20 > comparator. And if I should average the current during the PWM hold=20 > phase with an op-amp and then feed that to the comparator or A/D. I=20 > need to go tinker some more... >=20 > Cheers, > -Neil. >=20 I read a lot about PWM being used for Peak-Hold injectors but most people s= eem to be quoting the same source without doing any real research and I've = seen articles describing how PWM is used on certain ECUs that I know use cu= rrent feedback. I've tinkered with a good few P&H ECUs and worked on P&H in= jector designs for an OEM. The PIC A/D is likely to be too slow, particularly if its servicing a lot o= f other channels, a comparator based circuit is the usual method with a sin= gle comparator for the peak detect and a window comparator to maintain the = hold current within fixed limits. 0.5R seems quite high, I was working on a= n ECU today that uses a 0.27R resistor and its a 5W ceramic; the injector o= n that one is 1.5mH 1R at room temperature. James =20 --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .