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    hbridge control from mcu

    For implementing an hbridge, In the past I've connected an arduino to mosfets as in the fig. Click image for larger version. 

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    One mostet is a lowside switch and the other pmos is controlled by another nmos allowing the arduino
    to run it from 0-5V tho the power supply may be 20V for instance. (only one side of the hbridge is shown , other side is connected similarly)

    But i was wondering if I cant dispense with the extra nmos running the pmos by running the arduino output as an input which has high impedance - when in that
    state the pmos gate will go high , and when run as output at 0V the gate can be brought low.

    Click image for larger version. 

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    So far so good
    But the arduino input can only handle up to 5V, if connected as such the 20V will hit the arduino and cause trouble.
    I have the feeling there is some way to pull this off, can any one figure it out??

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    Re: hbridge control from mcu

    Use a diode, a transistor, a mosfet or a gate driver - your choice



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    Re: hbridge control from mcu

    Quote Originally Posted by summitville View Post
    Use a diode, a transistor, a mosfet or a gate driver - your choice
    On further thought ...
    The passive Diode does not allow for +5 Arduino and 12 volts on the Gate.
    So use a transistor, a mosfet or a gate driver - your choice

    Also consider,
    a) Minimum Dead-Time
    b) Gate drive current

    The Arduino forum has many threads regarding H-Bridges.



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    Re: hbridge control from mcu

    Thkx for your reply.
    My starting point was use of another transistor, which I had hoped to avoid with e.g. a diode or resistor network in some clever configuration.
    This may be impossible considering that I am looking for a ckt that drops 20V at 0A and drops ~0V at e.g. 1mA coming from the pullup - ie has a 'negative resistance', something only a transistor can do.



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    Re: hbridge control from mcu

    Hi,

    in some clever configuration.
    If there was a clever, cheaper, simpler ... solution ..... it surely is used by the big H-bridge manufacturers and you may find the circuit in the internet..

    There are many threads from hobbyists here that try to find/use simplified solutions....Most of them result in the use of known circuits.

    This doesn't mean that one should not look for clever solutions.. but from my experience it is rather seldom with a circuit like an H-bridge that is already usued billion times all over the world..


    Klaus
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    Re: hbridge control from mcu

    Some features that you usually want to achieve with a H-bridge gate driver
    - sufficient gate voltage to turn a standard MOSFET fully on, e.g. 8 - 12V
    - keep Vgs maximum ratings with varying supply voltage
    - source and sink sufficient gate current for fast switching

    Gate driver ICs are often an appropriate way to achieve this (least part count and lowest total cost) but discrete transistors are an option. Suitable circuits have been frequently posted at Edaboard.



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    Re: hbridge control from mcu

    I blv I have solved it , see fig below
    Click image for larger version. 

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    Quote Originally Posted by KlausST View Post
    Hi,


    If there was a clever, cheaper, simpler ... solution ..... it surely is used by the big H-bridge manufacturers and you may find the circuit in the internet..

    There are many threads from hobbyists here that try to find/use simplified solutions....Most of them result in the use of known circuits.

    This doesn't mean that one should not look for clever solutions.. but from my experience it is rather seldom with a circuit like an H-bridge that is already usued billion times all over the world..


    Klaus



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    Re: hbridge control from mcu

    Hi,

    There are free simulation software tools. Use them.

    Klaus
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    Re: hbridge control from mcu

    Here is my auto-biasing arrangement.
    H-bridge with 20 VDC supply, clock signal consists of 5v pulses biasing N-devices (low side).
    The P-devices (high side) receive bias signal from the opposite node of the H-bridge.
    Thus when a low-side N-device turns on, it pulls the opposite high-side bias low, turning it on. This sends full supply V to the opposite high-side bias, shutting it off. The load receives AC.

    Click image for larger version. 

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    Attention must be paid to make sure the nodes are close to 0V during one half of the cycle, and close to supply V during the other half of the cycle. If the nodes drift toward some midway voltage instead, then shoot-through may start to occur at higher current levels.

    Transistors are likely to work better because they start to turn on at 0.6V bias voltage.



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    Re: hbridge control from mcu

    unfortunately Mr Rutman, the simple ckt you propose will have shoot thru issues at every transition - at least you can turn this one off ...



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    Re: hbridge control from mcu

    Brad your circuit is similar, it looks like I have stumbled onto the known concept of autobiasing. Easypeasy I am not clear what you mean by shoot through, I blv. I need only keep both mcu lines off for some short time before turning any one on to prevent any transition issues.

    Extra credit - control both 'on' directions as well as 'off' using a single line.



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  12. #12
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    Re: hbridge control from mcu

    I blv I have solved it , see fig below
    A number of suggestions for appropriate gate driver circuit have been made in thread, you seem to try hard to ignore all of them.

    I am not clear what you mean by shoot through, I blv. I need only keep both mcu lines off for some short time before turning any one on to prevent any transition issues.
    Shoot through is a clear technical term, I believe. I understand that you only want bidirectional on/off switching, no pwm control. But did you verify that turning on a low side transistor doesn't cause temporary turn on of an unwanted path?

    Furthermore you still have insufficient gate voltage for the low side transistors and possible exceeding of Vgs,max for the high side.



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    Re: hbridge control from mcu

    5V is quite enough to drive the low side gates, actually, and in my case the 12V supply will not exceed the 20V max for Vgs on my pmos.
    I have seen no shoot through on a scope and the circuit works nicely.
    Thank you all those who took the time to reply !



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    Re: hbridge control from mcu

    I was referring to your provided info saying IRF540 and 20V supply.



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