h-bridge and large motors

Hi guys,
Let's say I have a small h-bridge driver like a TC4427 or a Tilden bridge built up from small transistors and I need to drive a larger
motor than the bridge can handle current-wise. Could I not just run the outputs of the bridge through a couple of non-inverting amplifiers or even let them invert, but let the software take care of direction control?
What would the circuit look like or would I have been better off building a beefier h-bridge in the first place? I'm looking to add a power transistor to each output to sink the current of the motor. I'm thinking that this would also add another layer of protection to the MCU.
What do you think?
Eljin
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Eljin wrote:

Well, first of all driving an H-Bridge with an h-brigde seems like a poor choice. For high current go with an H-Bridge made from two p-channel and 2 n-channel high current MOSFET transistors. There are a ton of schematics for this layout, and FETs don't rely on current based beta gain of a bipolar transistor, you can often drive them with CMOS logic circuits.
Make sure you use high speed flyback diodes because FETs are very vulnerable to the reverse polarity spikes from an inductive load. Make sure you use a small capacitor at the motor to clamp the really high spikes.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
mlw wrote:

I wasn't going to drive an h-bridge with an h-bridge. I just wanted to know if I could simply amplify the out put from a low current h-bridge to get the current needed to drive the motors.
I want to send the PWM pulse train through some kind of amplifier and the forward reverse line through a voltage ramp, probably the same type of amplifier, and attach that to my motor.
I'm trying to lower the parts count on the motor driver to make it smaller.
I was told I could probably do this with a couple of op-amps.
Eljin
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Eljin wrote:

Isn't that driving an H-Bright with an H-Bridge?

If you use FETs and CMOS logic, you need 2 AND gates, 2 inverters, the 2 p-channel and 2 n-channel transistors, a small cap for the motor, and 4 high speed/current switching diodes.

Opamps are great, but tend to be pretty slow. You probably won't be creating a high efficiency amplifier, so your frequencies will be in the low audio range, but still, something a long the lines of a fast opamp (TL092) or something.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.