New H-Bridge Design

Discussion in 'The Projects Forum' started by MatheusLPS, Sep 22, 2012.

  1. MatheusLPS

    Thread Starter Member

    Jul 16, 2011
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    So, I am desing one H-bridge from scratch because I have powerfull motors..

    So I tring to do something similar to it:

    http://www.mcmanis.com/chuck/Robotics/tutorial/h-bridge/bjt-circuit.html

    On that design the guy used just 3 pins to control the H-bridge.

    But I do not have those optcouples at home and I am trying top do something diferent.

    Please rate:

    [​IMG]

    On the simulation it is working...

    Thanks
     
  2. Audioguru

    New Member

    Dec 20, 2007
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    If you look at the datasheets for the darlington transistors, they already have R9, R10, R11 and R12 built-in.
     
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  3. ScottWang

    Moderator

    Aug 23, 2012
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    About the all Bjt H-Bridge circuit.
    If you like then you can combine Sw1,Sw2 become only one Sw1, you just add another PNP circuit as Q1 structure, connect the input of PNP circuit to forward pin, connect the C of PNP to backward pin, connect E of PNP to 5V.

    And then you just use one Sw1 to control the motor to move forward or backward.
     
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  4. MatheusLPS

    Thread Starter Member

    Jul 16, 2011
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    Thanks. I checked and on the first page of the datasheet I saw this. Less four resistors.. nice.

    @ScottWang

    I tried to do what you said, but i do not understand very well.

    May you draw it for me? Can be on paint :D.

    thanks
     
  5. ScottWang

    Moderator

    Aug 23, 2012
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    The Q9 PNP circuit added in the new circuit diagram.
     
  6. MatheusLPS

    Thread Starter Member

    Jul 16, 2011
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    ow ScottWang, thank's a lot! :D

    I do not know why, but the mod you posted do not worked _on the simulation_. But I changed the PNP with a NPN transistor and folowed your tip. It worked.

    With this circuit I can use a very small uC. Just 2 pins. Really nice.

    The final circuito with BJTs:

    [​IMG]

    Now, i wil try to adapt tis bridge to use with FET's..

    EDIT:

    Just make the mod here. Now it seems that work with FETs.

    Nice?

    [​IMG]

    bye
     
    Last edited: Sep 23, 2012
  7. ScottWang

    Moderator

    Aug 23, 2012
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    In the beginning, I want to use one PNP and one NPN, PNP for Hi, NPN for Lo, and I think only use PNP maybe will OK, but I forgot the Q8 still need a Lo level as GND, the 10K is too much, if use 300 ohm, probably it will work, but it still need to try, like you used NPN, that is what I want to use in the beginning, it just replace the original Sw2 function and connect to GND, the R10(10K) just replace the PNP function.
     
    Last edited: Sep 23, 2012
  8. ScottWang

    Moderator

    Aug 23, 2012
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    Many Rb(1K) are too small, you need to increase the value. (4.7K~10K)
    You lost some RB resistor at some B poles of transistors.
    The C resistors of Q5,Q7,Q9,Q11, I think you can use them up to 10K.
     
  9. MatheusLPS

    Thread Starter Member

    Jul 16, 2011
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    Thanks again ScottWang, I changed the values and it seems that is working.

    First I will mount the BJT bridge and when I got the FET's, I wil try the other.

    Ahhhh... before I forgot, look that I have +24V to feed the gate of the FET's. I wil show I little trick to transform +12V into +24V:

    [​IMG]

    With the doubler circuit this is easily accomplished.

    bye
     
  10. ScottWang

    Moderator

    Aug 23, 2012
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    The most application, We will use Vgs≦Vdd, so you used 24V for Vgs is unnecessary.

    IRF3205 datasheet.
    page 1
    VGS Gate-to-Source Voltage ±20 V ← this is the max voltage for Vgs

    page 2
    VGS(th) Gate Threshold Voltage 2.0~4.0 V ← This is the smallest Voltage for Vgs.
    http://www.datasheetcatalog.org/datasheet/irf/irf3205.pdf
     
  11. Audioguru

    New Member

    Dec 20, 2007
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  12. ScottWang

    Moderator

    Aug 23, 2012
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    Thanks for your Supplement.
    I posted the input voltage range of MOSFET, that just to tell MatheusLPS the Vgs is too high, and it's unnecessary.

    If you see that #8 I told MatheusLPS to reduce the input voltage, the voltage almost equal to the volage of motor(12V).
     
  13. help_mum

    New Member

    Sep 13, 2012
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    If you use I^RF389 HEXFETS you would only need 2, as you drive neg and pos. If I remember they are 30v 4to5 amps neg and up to 7.5 pos as gate drivers ROHM make twin NPN Transistors the last time I used them I tryed Hseries that have 4.5k internal resistors on the base pins but MX1 worked better. I would need to go back through my old Schematics. I think they were running at 1k
    Just a thought if you try this post the spice Specs on them please I would like to see how well they worked.

    HM
    Beginner
     
  14. MatheusLPS

    Thread Starter Member

    Jul 16, 2011
    34
    0
    Agreed. To solve this problem with the +24V I can feed the 555 with +6V and in the end it will be +12V.

    I am a bit confused with mosfets. I know that in the saturation mode:

    VGS > Vth and VDS > ( VGS – Vth )

    If I have this:

    VCC --> LED --> resistor --> Drain --> Sorce --> VSS.

    If VCC = 12V, Resistor = 470 ohms. And VGS is 10V.

    So 10V > 4V and VDS (?) > 6.

    In this case, how much is VDS?

    bye
     
  15. Audioguru

    New Member

    Dec 20, 2007
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    VDS is almost 0V (a turned on switch) when the VGS is 10V.

    EDIT: Don't even think about Vth since that is when the Mosfet is barely on and is almost turned off.
     
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