looking for some feedback to what i am seeing on my scope. let me set the scene.
its a driver circuit for driving fuel injectors. i made a bunch of dummy injectors which match exactly that of a real injector, yields 14.4ohms(dc) and 5.6mH inductance (two 27ohm wirewounds in parallel, then in series with the inductor). this driver gets its drive signal from a external source and will conduct current when the signal goes to ground. some parts from the scope was exactly what i was expecting, but other parts i am not yet sure of and will require me to do further investigating, but just wanted some feedback 1st to help steer my investigation. in this test i drive the circuit using my freq gen 60Hz @ 50% duty. voltage supply is 14.4v to ground. my signal drives a small npn and i tap off the collector to get the ground signal i need. this npn turns on/off very well into 300kHz range, so i dont see this causing any switching issues..... my application only runs from 0-60Hz. the pics stay the same regardless of drive frequency (other than their period of on/off, etc).
(click pics for bigger pic)
this 1st pic shows the switching. red is the signal driving my circuit. yellow is the wire coming from the fuel injector to the fet. fuel injector always has supply voltage on it on one side and i simply switch a nFet of the other side to control the current. as red goes low the fet conducts and current flows. when red goes high things turn off and i get a flyback spike clipped by 34v zeners.
this next pic shows some timing events
t1= 0.22ms, i dont know why the injector is still conducting current (or is it??). this may be because of the 1st drive stage i have using a pFET. the pFET may not turn off as fast as it turns on. as you can see in the above pic things turn on real fast.
t2= 0.116ms, simply looks like the magnetic field starting to collapse and voltage is generated until it reaches zener voltage.
t3= 0.2ms, looks like the time it takes for inductor mag field to decay.
t4= 1.54ms, a period of some ringing. not really sure what exactly is ringing down to supply voltage.
here's the ring up close. rings at 30.3kHz. hmmm, osciallation, but from where? perhaps some C in the inductor? not really sure.
its a driver circuit for driving fuel injectors. i made a bunch of dummy injectors which match exactly that of a real injector, yields 14.4ohms(dc) and 5.6mH inductance (two 27ohm wirewounds in parallel, then in series with the inductor). this driver gets its drive signal from a external source and will conduct current when the signal goes to ground. some parts from the scope was exactly what i was expecting, but other parts i am not yet sure of and will require me to do further investigating, but just wanted some feedback 1st to help steer my investigation. in this test i drive the circuit using my freq gen 60Hz @ 50% duty. voltage supply is 14.4v to ground. my signal drives a small npn and i tap off the collector to get the ground signal i need. this npn turns on/off very well into 300kHz range, so i dont see this causing any switching issues..... my application only runs from 0-60Hz. the pics stay the same regardless of drive frequency (other than their period of on/off, etc).
(click pics for bigger pic)
this 1st pic shows the switching. red is the signal driving my circuit. yellow is the wire coming from the fuel injector to the fet. fuel injector always has supply voltage on it on one side and i simply switch a nFet of the other side to control the current. as red goes low the fet conducts and current flows. when red goes high things turn off and i get a flyback spike clipped by 34v zeners.
this next pic shows some timing events
t1= 0.22ms, i dont know why the injector is still conducting current (or is it??). this may be because of the 1st drive stage i have using a pFET. the pFET may not turn off as fast as it turns on. as you can see in the above pic things turn on real fast.
t2= 0.116ms, simply looks like the magnetic field starting to collapse and voltage is generated until it reaches zener voltage.
t3= 0.2ms, looks like the time it takes for inductor mag field to decay.
t4= 1.54ms, a period of some ringing. not really sure what exactly is ringing down to supply voltage.
here's the ring up close. rings at 30.3kHz. hmmm, osciallation, but from where? perhaps some C in the inductor? not really sure.
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