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Topic: MOSFET + H-Bridge for ultra low power (Read 1 time) previous topic - next topic

Busaboi

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.

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  :(

Busaboi

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?


Anachrocomputer

This board:

http://store.gravitech.us/mi5v3lesh.html

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/

Busaboi

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.

http://www.sparkfun.com/commerce/product_info.php?products_id=8745

rocketgeek

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.

Busaboi

@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?

Anachrocomputer

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

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