Hello all, I have a 24VDC 1A brushed DC motor, but I have a 28V power supply. I was wondering if I could use zener diodes to regulate the voltage down to 24V. This seems doable until I consider changing the polarity to switch the motor direction. Does anyone know of a creative design that uses zeners that would allow me to still switch motor direction?
Any help would be great.. Thanks, Lucas.
You could put 4 diodes and a bridge in series with the motor: (view with fixed-width font)
+---+ | | .-----. | V A -|~ +|---+ - B -|~ -|---+ | '-----' | | | V | - | | | | | V | - | | | | | V | - +---+Diode rating depends on the motor specifications (including stall conditions).
Or put a zener (or a TL431) where you have the four diodes.
...Jim Thompson
See figure 21 for how to boost a TL431A to a few Amps ;-)
3.1 3.1 motor --->Z---Z
28V supply ---> Zener ----> reversing switch -----> motor
Thanks for the replies, the issue we're having is that the polarity switching must happen "before" the voltage step down. So the circuitry must be able to work independent of the polarity. See below
______________________ | | ________ (+28)------| |-----(+24)-----| | | Voltage Regulation | | Motor | CW Rotation (Gnd)------| |-----(Gnd)-----|-------| | | ----------------------
______________________ | | ________ (Gnd)------| |-----(Gnd)-----| | | Voltage Regulation | | Motor | CCW Rotation (+28)------| |-----(+24)-----|-------|
We need to place the voltage regulation circuit "between" the 28V and the motor knowing that the 28V may switch in order to switch the direction of the motor. Does this make sense?
Again, any idea would be great. We're trying to keep the number of parts to a minumum (due to PCB size requirements) thats why I thought zeners would be the easiest.
Thanks again, Lucas.
A requirements change this late in the project is going to cost you.
You'll have to use two zeners, two diode strings, etc.
Hey! It's the standard 780x/PMP booster circuit, sideways! ;-)
Cheers! Rich
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