# Can you help? Analog Polarity switch problem.

Discussion in 'General Electronics Chat' started by medonno, Feb 21, 2009.

1. ### medonno Thread Starter New Member

Feb 21, 2009
2
0
Hi! Anything that I learnt in college about electronics evaporated already.
Now I can't even sort this little problem out. I am trying to build a switch that changes polarity every time an object travelling on a rotor of a motor crosses light beam of a photo sensor. This should be an analog switch with no mechanical parts, something like MAX303, but should be able to handle continuous current of up to 10A DC and voltage of 12v DC to 36v DC and be able to switch tens of cycles per second. Probably it will make use of power transistors.
I am sure units like that are being manufactured, I just don't know where to look. May be that you know the answer? I would much appreciate your advice.

2. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
For that kind of power, you will need to look into an H bridge. I assume those are reversals per second - an H bridge can handle switching into the tens of thousands of Hz.

3. ### medonno Thread Starter New Member

Feb 21, 2009
2
0
Many thanks! This was the answer I needed. An H bridge using chip such as TC4424 feeding power MOSFETs will do nicely. I was stuck and you enlightened me. Thanks once more.

4. ### eblc1388 Senior Member

Nov 28, 2008
1,542
102
Switching a H-Bridge with high frequency means chopping the current and is vastly different to driving a motor rotor to reverse rotation 30 times a second. The H-Bridge does its job OK but this does not means the motor will rotate as desired.

Because of the mechanical inertia of the rotor, the motion pattern requires high starting and braking torque, high current and definitely not an easy task to achieve.

With this high rate of direction changes, the rotor would just vibrate instead of rotating in the desired direction.

Please post back with your findings on the actual motor performance.