Adding diodes in series

Discussion in 'DIY Discussion' started by locky, Jun 20, 2005.

  1. locky

    NRG

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    If we use your existing TX and assuming 10% regulation after rectification you will have approx 35-36v. With Ia peak at 5A your TX needs to be 350Va.

    I would not use a resistor in the supply, as current demanded by the load IE during bass transients, will cause the voltage drop to increase/vary accross the R. I would regulate the supply.
     
    NRG, Jun 22, 2005
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  2. locky

    wadia-miester Mighty Rearranger

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    Further to NRG's points above, I would personally use a seperate tx for the 5v supply (irrespective if the one you are using has another tap) and use some quality res & smoothing caps, shocktty diodes, and one of Andy weeks Super regs or similar, I can't stress enough how import the supply to the tripath chip is and how much of a different can be wrought.
     
    wadia-miester, Jun 22, 2005
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  3. locky

    locky

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    Thanks again for the replies...
    The TX is rated at 330va. Once rectified at the diode bridge and then regulated through the LM338, will this be enough? Also...if I go down the LM338 route what rating of heatsink do you think would be acceptable? If these regulators can handle it then I think I'll take this route. An additional TX for the 5v supply would be good, but I'm planning on taking a bridge from the +35v rail and building a 5v regulated supply from this. I can always adapt and upgrade things later I suppose. Until I get the PSU sorted I don't even know if the module I've built actually works...
     
    locky, Jun 23, 2005
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  4. locky

    felix part-time Horta

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    Use a regular LM317 and LM337 regs, with external pass transsitors sized to handle the current. This is cheaper than 338s, can handle far more current and will probably do at least as good a job of regulation.

    You can use LM317s and the like at any voltage, the voltage limit is the differential across the chip. If you place say a 15V/5W zener reverse-biased across the input and output pins you can use them at >37v supplies - because the startup current to charge any caps on the output passes throug the zener. Once running, the zener drops out of circuit and regulation is entirely handled by the 3-pin reg. It's an easy wasy to build 400+v regulated supplies...
     
    felix, Jun 23, 2005
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  5. locky

    NRG

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    NRG, Jun 23, 2005
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  6. locky

    locky

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    The LM338 seems to be a positive regulator. Wouldn't I also need one for the negative rail?

    'You can use LM317s and the like at any voltage, the voltage limit is the differential across the chip. If you place say a 15V/5W zener reverse-biased across the input and output pins you can use them at >37v supplies - because the startup current to charge any caps on the output passes throug the zener. Once running, the zener drops out of circuit and regulation is entirely handled by the 3-pin reg. It's an easy wasy to build 400+v regulated supplies...'

    Wouldn't the current, however, still be limited by the LM317? The LM338 gives me a guaranteed 5A output current.
     
    locky, Jun 23, 2005
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  7. locky

    felix part-time Horta

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    Not if you use an external pass transistor.
     
    felix, Jun 23, 2005
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  8. locky

    NRG

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  9. locky

    locky

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    Thanks,
    That's very helpful! I have decided to use a separate TX for the +5v supply. This will consist of a 7v TX fed through a bridge diode rectifier and then regulated. Any recommendations for a decent regulator for 5v 100ma? Also - I only need the + 5v rail. Does this mean I leave the -ve from the bridge diode disconnected?
     
    locky, Jun 24, 2005
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  10. locky

    wadia-miester Mighty Rearranger

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    Lm 323 T
     
    wadia-miester, Jun 24, 2005
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  11. locky

    NRG

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    Or LT1086CT-5 (fixed), LT1086CT adjustable
     
    NRG, Jun 25, 2005
    #31
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