Best and most off-the-shelf way to drive a MOSFET from 3.3V

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daqq
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Posted by daqq: Tue. Jan 1, 2013 - 12:49 PM
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Hi guys,

I'm trying to drive a MOSFET by an AVR running at 3.3V for a upward DC DC converter. What would you recommend as the best solution for driving it? It should be as available as possible.

I'm thinking of a MAX232 (or one of its 1Mbps siblings) might do the trick. The charge pump should provide sufficient voltage, but I'm worried about the negative voltage on the gate. Could it do anything bad?

The FET in question is http://www.thierry-lequeu.fr/dat... (or similar).
The control signal should be a 10 kHz PWM signal.

Thank you,

David

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alexan_e
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Posted by alexan_e: Tue. Jan 1, 2013 - 01:01 PM
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Do you have any voltage higher than 3v3 available?
If you do then you could use a mosfet driver like TC4427 http://ww1.microchip.com/downloa...

How exactly is the mosfet wired, is it a low side switch?

Alex

"For every effect there is a root cause. Find and address the root cause rather than try to fix the effect, as there is no end to the latter."
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Torby
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Posted by Torby: Tue. Jan 1, 2013 - 04:30 PM
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Another mosfet with a "logic level" threshold and a resistor usually works for me.

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glitch
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Posted by glitch: Tue. Jan 1, 2013 - 08:45 PM
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we need to see the circuit. as it makes a difference if it is a N or P fet, and high-side or low-side switching.

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ka7ehk
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Posted by ka7ehk: Tue. Jan 1, 2013 - 09:05 PM
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Use a charge-pump doubler to create the higher voltage needed for gate drive? Example: the venerable (ICL/LMC/...)7660,

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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daqq
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Posted by daqq: Tue. Jan 1, 2013 - 10:21 PM
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Hi guys,

thank you for the replies.

The FET in question is on the low side and is an N FET, the link to the datasheet is: http://www.thierry-lequeu.fr/dat... , see attached schematic (note: values in the schematic are just preliminary, will change, even the FET is different than in the schematic as I've noticed later!).

Quote:
Use a charge-pump doubler to create the higher voltage needed for gate drive? Example: the venerable (ICL/LMC/...)7660,
Yup, that's exactly what I had in mind with the MAX232 or similar, with the added function of a logic level translator and being very common.

The output voltage for the converter should be around 50V, the input is anywhere from 3V to around 24V. I'd love to use the input voltage, however, the low part of the range might not open the gate enough.

Quote:
Another mosfet with a "logic level" threshold and a resistor usually works for me.
I thought about that, but there's a nasty power consumption when I want better edges. I might use it, but first I'd like to explore the other options.

Attachment(s): 

Image icon Untitled.gif

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Torby
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Posted by Torby: Tue. Jan 1, 2013 - 11:38 PM
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You could always use a pfet 'stead of a resistor.

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alexan_e
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Posted by alexan_e: Wed. Jan 2, 2013 - 12:21 AM
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Quote:
the input is anywhere from 3V to around 24V

Is this the same source that feeds the AVR?
What king of regulation are you using to get a steady Vcc?
Can that Vcc also be used for a charge pump circuit or it would have to work from a variable 3-25v supply?

This driver can achieve a low consumption and good performance compared to the single transistor/resistor driver.

If you want a faster switching performance you can also add a totem pole to the output.

As a charge pump you could use a discrete circuit like the following driven by the AVR

The supply voltages for all these is still an issue.

Alex

Attachment(s): 

Image icon discrete charge pump
Image icon mosfet driver

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daqq
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Posted by daqq: Wed. Jan 2, 2013 - 08:21 AM
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@Alex: Thanks! I'll look into these, they look very promising!

There are pointy haired bald people.
Time flies when you have a bad prescaler selected.

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