Re: PWM

[Subscuba <Subscuba@aol.com>]

Brian,

If I understand your question correctly, all you want is ON/OFF switches to
interface between your 5 volt logic and the motor including reversing.

I would suggest a  full bridge also called a H bridge of four MOSFETs. You
could use two P channel FETs for the upper devices and two N channel FETs for
the lower devices. The P channels could be International Rectifier IRF4905-ND.
The lower FETs  IRFZ46N-ND. The power dissipation would be about 3 watts per
FET when the FET is on and carrying 10 amperes. Heat sinks would be required.
The devices can be purchased from Digi-Key at 1-800-4539. This assumes that
you are not using PWM techniques and that you would only switch the motor on
or off. This also permits you to use the body diodes in the FETs for the motor
inductance flyback (a sometimes risky thing to do due to body diode reverse
recovery). Take a look at the Unitrode 1997 applications manual note U-102
Figure 8 page 3-73 for an example of the H bridge topology. The UC1637 could
be used to do what you want with some interface circuits. This application
note would prove useful to you and shows a PWM technique with current limit.
Unitrode has a website you can download from and you should be able to find
this application note (http://www.unitrode.com). As you are aware don't take
application notes too seriously, they are primarily sales oriented and have
disclaimers.

Be aware that the di/dt of modern MOSFETs can exceed the di/dt of Emitter
Coupled Logic (ECL) by 100 times so layout is critical. Lead lengths to the
motor is not very critical but to the power source is. Local bypassing with
low Q capacitors is usually required.

I am also a EE. Shayne, you might also be interested in the application note.

Brian, copy to Psubs when you send messages to me. Thanks!

Good Luck,

Ken Martindale