4g63 "Unipolar" stepper IAC(6 wire stepper)

[devojet]

PNP's can be used to switch to ground. Basically BJT transistors operate on current flow. PNP's switch when current is pulled from the base and NPNs switch when current flows into the base. This is a very basic disciption and there is a lot more to it.

Anyway back to the IAC topic, Off hand you could use a TIP125 with a 2.4Kohm resistor. This might be overkill though as the tip125 can handle up to 5A and is a TO220 package device. Any PNP with a high enough current rating can be used. You just need to calculate the resistor size based on the current gain of the transistor or send me a data sheet and I will let you know if it's suitable and what resistor to try.

Cheers

Daniel

[arkadi]

I think just two diodes may work, see attached picture.
What you think? When driver reverses polarity, another half of the winding will be grounded, like in factory setup. No need to disconnect center tap. And you get better torque because of higher current.
Even the diodes are not required, the current won't flow from +12 to +12 until there is a voltage offset.
The rationale behind this is:
- If you open the block diagram of bipolar driver (UDN2116) and unipolar driver (NJM3517) you'll see that unipolar driver is just half of bipolar.
- The two halfs of (unipolar motor) stator winding are wound in the same "place" but in opposite directions. The missing logic for voltage reversal is solved by connecting oppositly positioned taps (but pictured as single center tap) of "half-winding" to the battery permanently. Half of the winding is wasted in unipolar motor.
More on http://en.wikipedia.org/wiki/Stepper_motor and its' External links section.

[devojet]

You correct that would probably work without the diodes. The reason we were talking about adding transistors was that there were doubts if the IAC chip could drive enough current for some stepper motors.

Cheers

Daniel

[arkadi]

The reason we were talking about adding transistors was that there were doubts if the IAC chip could drive enough current for some stepper motors.

By no means I'm an electrical engineer, but:
- I believe you should first try with "center" tap connected. This will not half your magnetic field, because its strength depends on the current, not how much you invest in winding wires.
- UDN 2916 has PWM for over-current protection and can sustain 750mA which is pretty much enough for an IAC stepper.
- Adding transistor can actually harm because the driver can't sense the output and because of non-linear natures of motors (inductivity) and fast polarity reversal the actual current can be more than acceptable.

[Peter Florance]

The reason we were talking about adding transistors was that there were doubts if the IAC chip could drive enough current for some stepper motors.

By no means I'm an electrical engineer, but:
- I believe you should first try with "center" tap connected. This will not half your magnetic field, because its strength depends on the current, not how much you invest in winding wires.
- UDN 2916 has PWM for over-current protection and can sustain 750mA which is pretty much enough for an IAC stepper.
- Adding transistor can actually harm because the driver can't sense the output and because of non-linear natures of motors (inductivity) and fast polarity reversal the actual current can be more than acceptable.

I suspect the current will be cut in half, but driving that way will probably work anyway as long as the valve is in good condition and clean.

[md95]

I really haven't tried anything else with the stepper, because, well, it's been working fine 100% for quite a while now. I still have that not going to cranking steps issue though at cranking sometimes..thats a "commanded" issue, not a IAC stepper moving issue though. Haven't had much time to figure that one out yet. I have an idea or two, just need to try it. It works fine on the bench, but in the car it gives the issue. Strangest thing i've ever seen.