I'm attempting to emulate a variable reluctance sensor on an engine. I know I need to produce a 600hz-6000hz zero-crossing +/-12volt waveform. The engine management controller's input measures 20okhm.
My first attempt used a Bourns SM-LP-5001 1:1 audio transformer for isolation. My LM2904 went into current limiting mode when I fed it any waveform on CKP1/CKP2. My assumption is that I mismatched something causing the current to exceed the LM2904's capacity. VIN is nominal automotive 12VDC, I am using 13.9VDC for my bench supply.
Here's what I'm thinking for my next attempt, but I need some understanding how to specify what transformer I need.
I found a Xicon 42TM018-RC audio transformer that has 1:1 10k CT winding and 550 ohms DCR on it's primary.
- Since the ECM measured 20kohm at it's inputs with my DMM, does my transformer need to match 20kohm primary impedance?
- Or will this circuit fail for a different reason?
- Is there another approach that would work better?