LM311 H-Bridge driver

Spike Maul Mar 9, 2019

  1. Spike Maul

    Spike Maul TrainBoard Member

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    Hi Folks. I've designed an H-bridge driver using LM311's. It works well
    with dcc++ and jmri. I've made KICAD files and produced PC boards
    and the circuit has been used with straight transistor drivers for
    a programming track buffer, power darlingtons as a booster, and
    "external" discrete device darlington outputs and they all have worked
    nicely. I've also tested the board with Dani's loko-net (sic) arduino
    code and it likewise works well. I've a short writeup here:

    https://dcc.wraith.sf.ca.us//

    Spike Maul
     
    bocabob likes this.
  2. bocabob

    bocabob TrainBoard Member

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    Spike, very interesting. How much of this depends on 5v signals. I'm heading down the 3.3v ESP32 path, so while I can provide 5v VCC, the signal pin max is 3.3v. Also, I was googling the various transistors you note in your write-up, if I wanted the 8A 2n6041/2n6044 where would they go on the board? I'm an ME, not a EE, so am a bit limited in my electronic knowlege :)
     
  3. Spike Maul

    Spike Maul TrainBoard Member

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    Hello bocabob--the H-bridge "should" be ok with 3.3v PWM and enable signals.
    I've not tested it but the inputs are simple 2n2222's, not logic gates, so there should
    be no problem. "should, cough"

    The output transistors should be selected for their power rating. That "8 amp" rating
    of the 6041/44's will not be possible in a 15volt circuit, since it exceeds the power
    rating of the devices. I rate that pair as good for 5 amps/15 volts. Another set
    might be tip100/tip105. The devices were laid out at the edge of the board
    so that I could more easily provide adequate heat sinking.

    Especially, power darlingtons do heat up.

    INSURE ADEQUATE HEATSINKS.

    A small fan, such as out of a scrapped AT power supply, or an old computer
    case fan, should be part of an installation of this board with high power transistors.

    Installing output transistors: With the input connector close to you, the left side
    has (reading up) bce/bce and the right side ecb/ecb (always double check).
    The power input are the right two vias in the center top, and the track output
    are the left two vias. I've installed a couple of the screw terminals to do testing,
    but I prefer to "hard solder" if I have a choice.

    I've been learning these lessons since the 70's so sometimes I take knowledge
    for granted.

    Spike Maul
     
  4. bocabob

    bocabob TrainBoard Member

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    Spike, got it, watts on the power dissipation rating.

    I take it from your post that the power rating (which I assume is for the pair) is the rating for the 4 transistor bridge and is not the sum of the two pairs?

    so Tip 100/105 is 80W which is about 5A for a 15V HO track
    Tip 110/115 is 50W, ~3A @ 15V
    Tip 120/125 is 65W, ~4A @ 15V
    Tip 140/145 is 125W, ~8A @ 15V

    Yes, I think a fan header would be a required addition to the board!
     
  5. bocabob

    bocabob TrainBoard Member

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    In looking at the BOM to build this, could you provide ratings for the below?
    Ref Qnty Value
    C101, C102 2 47
    C103, C104 2 .1
    C105 1 .22
    D101, D102, D103, D104 4 DIODE Device:D Diode
    R101, R102, R103, R104, R105, R106 6 620
    R107 1 .1
    R108, R109 2 300K
    R110, R113 2 510
    R111, R112 2 39K
    R114, R115 2 15K
    R116 1 1K
    R117, R118 2 4K7
    R119, R120 2 470

    sorry about the formatting but all my efforts to do a table have failed
     
  6. Spike Maul

    Spike Maul TrainBoard Member

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    The c101/102 take a beating in the thor circuit. They should be low ESR aluminum electrolytic
    of 2000 microfarad, 25 volts, 105C rating. The 85C rating will "work" I suppose.
    I used the 47uF/35v solid tantalum in the '6041/44 darlington and they got warm.
    At first I had 22uF tantalum in there, and they got quite hot. Finally I piggybacked
    some 2200uF/25V low ESR aluminums in there and that made the power circuit purr.
    BTW I powered it up with *no* capacitors there, and all the decoders laughed out loud.
    Literally, they all blinked their headlights.

    The .22 and .1 capacitors should be 50v. Resistors 1/4w 5%.
    Current sense resistor .025 ohms several watts non-inductive for the power driver.
    As for the diodes, a set of 1n5403's worked for me. I also used mr851's. Freewheeling diodes,
    peak forward current surge 100 amps. Use of 1n400x devices is not recommended.
    Spike Maul
     
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  7. Spike Maul

    Spike Maul TrainBoard Member

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    Last night I had a power darlington block under test. This unit was built up with just a
    1/4 watt resistor lead as the "current sense" "resistor." When I opened up a "display
    dcc++ traffic" window in jmri, I noticed that good current sense readings were being
    sent to jmri from the arduino dcc++ software. Using the two amp brake sled as a load,
    I was seeing dcc++ deliver a "15/1024" reading to jmri.

    Looks like the higher current versions of the lm311 H-bridge driver could simply use
    a jumper for the sense point.

    BTW the "track current" window in jmri has not worked for me since jmri4.10.something.
    Spike Maul
     
  8. Atani

    Atani TrainBoard Member

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    There is likely a bug in JMRI for this, what sort of issue are you seeing though?
     

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