Victor 884 output decoding / General question

[Al Skierkiewicz]

Jacob,
I am not sure I understand your application fully. Are you using a standard PWM signal as an input? If so, the PWM does not change polarity. The pulse width relates to a 256 step decode where 0 is full throttle in one direction and 255 is full throttle in the other direction with 127 decoded as stop. The current Victor design decodes this PWM signal after some input signal conditioning and then uses the data to produce a proportional PWM output at a repetition rate of 120 Hz. The IFI website has some great discussion on the operating parameters and input PWM and decoded output.


If you are trying to perform a similar function with a custom controller then your circuit might work. If you are able to send PWM to one pin for forward and another pin for reverse that would simplify things a little. I see a few things as not needed and few things missing. The diodes would not be needed for instance since a FWD or REV signal would feed a dedicated input. You will need some input conditioning to insure that the device is getting reliable signals, a little low pass filter for RF protection and a few zeners to ground if there is a distance between your control and the drivers. The FETs need some resistors on the gates to make sure they turn on and off and so you don't blow them up, so check on FET design and applications. You need some way to determine "off" and could easily decode that from an absence of signal on either input pin. Then you want to make sure that the FET you use has some reverse voltage protection for when the motor is running with no drive signals. The FET the 884 uses has a reverse diode built in. Don't forget a little power supply filtering to prevent false operation and I think you would be close.