MOSFET + H-Bridge for ultra low power

Forum 2005-2010 (read only) Hardware Interfacing
1

I'm using an SN754410 to control a DC latching solenoid. I'm sleeping the Arduino, wake on ext interrupt, pulse the solenoid open then close, then back to sleep. The solenoid is wired like a bi-dir motor to pins 3 & 6. http://itp.nyu.edu/physcomp/images/labs/hbridge_labpinout.jpg

All is good but the idle/standby/quiescent/leakage current of the hbridge VCC1 (pin16) is around 10mA, so too much for something I want to go at least a year b4 changing batts.

My lil noob brain thinks a MOSFET could be used to control power to VCC2 so it only draws current when pin enabled by the 'duino. I just can't see how to wire it in.

Any help would be appreciated.

thx

sorry, i don't see an upload button to show my schematic :frowning:

2

So I figured out how to use the enable pins to shut the h-bridge down. Now my challenge is to boost the 3.3v arduino mini signals up to 5V so the logic levels on the h-bridge can be toggled. I've tried using the MOSFET but it's NPN and inverts the signal. I've also tried a PNP BJT but no joy.

Any ideas?

3

This board:

uses a TI 74LCX245 chip to do the level shifting. I'm sure there are others that would work, too.

There's an interegsting blog posting here on the same subject, but for bi-directional level shifting:

http://www.rocketnumbernine.com/2009/04/10/5v-33v-bidirectional-level-converter/

4

Thanks AC! The gravitech item is slick.
I'd been doing some digging and also found the same app note. The good thing is that I found the following after noodling about how to wire the bi-dir shifter up.

5

Anachro: that blog posting references a Phillips app note (http://www.nxp.com/acrobat_download/applicationnotes/AN97055.pdf) which is worth reading because it's pretty slick.

6

@AC: So I built a proto using an STB24NF10 NPN MOSFET just to try. It works but I can only get 2.5V into the h-bridge. Could the current draw for the h-bridge plus the 10k resistors be dropping the voltage? Do you think smaller resistors are worth trying?

7

Hard to say. If you have smaller resistors, I suppose it'd be worth trying.