Brushed DC motor driver

[lmcgill2]

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.

 

[Spehro Pefhany]

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).

 

[Spehro Pefhany]

Or put a zener (or a TL431) where you have the four diodes.

...Jim Thompson

http://focus.ti.com/lit/ds/symlink/tl431.pdf

See figure 21 for how to boost a TL431A to a few Amps ;-)

 

[Jasen Betts]

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?

3.1 3.1 motor
--->Z---Z<---[O]---
5W 5W

seems crazy to me.

 

[lmcgill2]

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.

 

[Rich Grise, Plainclothes Hippie]

http://focus.ti.com/lit/ds/symlink/tl431.pdf

See figure 21 for how to boost a TL431A to a few Amps ;-)

Hey! It's the standard 780x/PMP booster circuit, sideways! ;-)

Cheers!
Rich