# Low voltage H bridge

Discussion in 'General Electronics Chat' started by Navarr0, Feb 24, 2015.

1. ### Navarr0 Thread Starter New Member

Oct 10, 2013
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0
Hello, please, I need help. I have MCU with LED display, both powered from two AA batteries with DC 5V converter. Now I need control little DC motor (1.5-3V and current max 500mA). So I wanna build H bridge controled with 5V voltage from MCU. Can you tell me, if this circuit will work? http://www.electro-tech-online.com/i.../3304-idea.JPG. H bridge must be powered directly from two AA (cca 3.2V when new). I wanna use four n-channel mosfet TSM2302CX with Vgs(th)=0.95V. For low side nfet there is Vgs=5V without problem. But for high side nfet there is 5V-3.2V when open =1.8V, so it's still good? Thanks for response.

2. ### MikeML AAC Fanatic!

Oct 2, 2009
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No. Use low-threshold NFETs for the bottom pair, and low-threshold PFETs for the top pair.

3. ### Navarr0 Thread Starter New Member

Oct 10, 2013
4
0
Thank you. Mosfets with the lowest threshold voltage what I can get are NFET TSM2302CX with Vth=1.2V(max) and PFET TSM2301CX with Vth=0.95V(max). Do you think that't enough?

4. ### MikeML AAC Fanatic!

Oct 2, 2009
5,451
1,071
I would write your program so as to use four port pins to control the four FETS. A high turns on the NFETS. A low turns on the PFETs. Put a delay so that you write a low to the opposite PFET after you write a high to the NFET. Put a delay so that you write a high to the PFET before you write a low to the NFET.

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5. ### Navarr0 Thread Starter New Member

Oct 10, 2013
4
0
Ok that's clear, thank you very much .

6. ### MikeML AAC Fanatic!

Oct 2, 2009
5,451
1,071

The resting state (motor freewheeling or not running) is two lows to the NFETs; two highs to the PFETS.

To brake the motor, both NFETs high, both PFETs high.

But never turn on both the NFET and PFET on either side of the h-Bridge at the same time!