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Low input current Half Bridge driver ... — Parallax Forums

Low input current Half Bridge driver ...

Beau SchwabeBeau Schwabe Posts: 6,568
edited 2010-06-10 08:27 in General Discussion
I wanted to throw this out in the forums for a proper litmus test.


This type of circuit seems to be popular lately ... Something for the EXPO, I needed a relatively low input current (about 1mA) to adequately drive (with at least 150mA) the gates of a couple NMOS and PMOS transistors, and I wanted the high side drive verses the low side drive to be equally balanced or at least close. In simulation I took this up to 25kHz and loaded the gate capacitance of the MOSFETs with 0.01uF ... no problems that I could tell.

If the Input is left floating, the OUTPUT defaults to being driven LOW via the hard wired 100K resistor. For opposite operation wire the 100K to GND instead.

The circuit is designed to accept TTL output where you have a 0.6V buffer on either power rail but it will work with CMOS output also.


Edit: The attached image (The lost art of perf-boarding) shows the circuit minus the MOSFETs

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 6/10/2010 4:32:09 PM GMT
225_0020.JPG
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Comments

  • HollyMinkowskiHollyMinkowski Posts: 1,398
    edited 2010-06-09 09:00
    Perf-boarding is not a lost art!
    I'm keeping it alive..lol
    My projects look really good unless you
    turn the boards over smile.gif
    I just can't justify the cost of a single custom
    board as long as I can make an ugly go of it
    with a piece of cheap perf board.
  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2010-06-09 09:13
    Ok Holly, you asked for it [noparse]:o[/noparse])


    BTW) ...been doing some testing since my original post and this driver has worked out really well

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    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
    Front.JPG
    2304 x 1728 - 465K
    Back.JPG
    2304 x 1728 - 452K
  • HollyMinkowskiHollyMinkowski Posts: 1,398
    edited 2010-06-09 09:22
    LoL smile.gif

    The backside of that board looks really familiar to me.
    It's actually harder to do the rats nest of point-to-point
    wiring beneath a perf board project than it is to do sm
    construction on a custom board.
  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2010-06-10 03:32
    Based on what I have seen on the scope, this circuit should be good for about 650kHz... The weak link is in the falling edge which could be made 'sharper' by lowering the two 10K resistors that form a divider to the base of the 2n3906. Whatever value, they should both be the same value. What happens is that the lower NPN turns 'on' while the upper PNP is still in the process of turning 'off'. The overlap is small, but it is enough to limit the speed. On the other hand, the rising edge is very fast ... upwards of 2MHz.

    In my particular application I won't be going much over 5kHz so this time I will leave it the way it is.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2010-06-10 04:39
    **Finally** pleased with the results of this circuit, but I just realized I need to put together a schematic for this thing ... smilewinkgrin.gif

    You can see where the Half bridge driver is being used, about middle of the Solderless-Bread-Board, and the two MOSFETs to the right.

    Hopefully this will be 1 of about 4 things I want to demonstrate at the EXPO ... we'll see how things go if that will happen or not.

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    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
    MPPT.jpg
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    MPPT.jpg 116.5K
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2010-06-10 08:27
    Beau,

    Is the PMOS transistor symbol flipped in your schematic?

    -Phil
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