low voltage h-bridge. - Page 1
Forum section: electronics / projects

author: Vgkid
author_rank: Super Contributor
timestamp: October 23, 2016, 08:44:57 pm
content: Would it be possible to switch either in an H bridge configuration , or half bridge. A voltage ranging from 1 volt to to severall hundred millivolts. The current will be up to 20A. I have seen H-bridge circuits for 1v and up. The drive voltage is not limited.

author: Zero999
author_rank: Super Contributor
timestamp: October 23, 2016, 08:59:20 pm
content: Yes. Use N-channel MOSFETs for both the high and low side.

author: Zero999
author_rank: Super Contributor
timestamp: October 23, 2016, 09:26:01 pm
content: MOSFETs are available nowadays with a very low on resistance below 1mUse the IRFS7430 which is guaranteed to have an on resistance of less than 0.75m, giving a voltage drop of under 30mV for two in series, if driven from 12V. If the resistance of the PCB is a problem, then mount them on thick copper bus bars.http://uk.rs-online.com/webdocs/13c7/0900766b813c79c2.pdf

author: grifftech
author_rank: Frequent Contributor
timestamp: October 24, 2016, 03:04:29 pm
content: relay

author: leeatljs
author_rank: Contributor
timestamp: October 24, 2016, 03:18:51 pm
content: As noted, at these currents, mosfet voltage drop is significant.You could increase the output current of an op amp by buffering its output with mosfets, a quick google search turned this uphttp://www.allaboutcircuits.com/technical-articles/how-to-buffer-an-op-amp-output-for-higher-current-part-2/The op amp would then compensate for mosfet voltage drops.What sort of speed are you switching the output?

author: Siwastaja
author_rank: Super Contributor
timestamp: October 24, 2016, 03:35:53 pm
content: Relays are easily much more resistive than MOSFETs, so it's not a good suggestion. Low contact resistance relays are big and expensive. A big, beefy MOSFET is the way to go; you can directly solder it on the copper busbar, minimizing extra contact resistance. Look for MOSFETs with as low Vdsmax as possible, the one given as an example above was 40V, which increases gate capacitance and requires higher gate voltage, for no benefit whatsoever. 20V rated MOSFETs give smaller resistance per price as well as per gate charge.And you can always parallel the mosfets.Make your own busbars from copper sheets, directly solder the FET. If you do this, the important question becomes:What are you driving with this bridge and how you are going to physically connect it? In many cases, integrating the thing you are driving to the same copper busbars would make sense, if possible.

author: Zero999
author_rank: Super Contributor
timestamp: October 24, 2016, 03:43:23 pm
content: Quote from: Siwastaja on October 24, 2016, 03:35:53 pmYes, you're right. No doubt there are MOSFETs around with a lower on resistance. I just searched RS Components with the filter set for MOSFETs with the lowest on resistance. Better parts will be available from other distributors and do make sure you use a decent supplier, not just off eBay as there are lots of fakes about.

author: Vgkid
author_rank: Super Contributor
timestamp: October 24, 2016, 06:16:15 pm
content: The other idea I had was to create an amplifier set up for unity gain, but acting as a high current buffer.