So, I need to step 12 V up to 30 V, what are some approaches?

Discussion in 'General Electronics Chat' started by hrstar24, Oct 18, 2011.

  1. hrstar24

    Thread Starter Active Member

    Apr 7, 2009
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    I am designing a power circuit right now, and I currently have a 12 V battery as a source, and I need to step it up to 30 V for the rails of an op amp.

    I have been thinking about maybe using a boost converter, but I am not too sure. Anyone have any suggestions? Maybe a transformer or something?
     
  2. #12

    Expert

    Nov 30, 2010
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    Transformers don't work with DC current. The boost converter is the best idea. Try the National semiconductor simple switcher site for a free design of 12 to 30 or 12 to +/- 15V.

    There are 2 other sites that will do that for you, but I don't know which ones. Somebody else will come along and name them.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    If you're not too particular about regulation, don't need much current, and you just need something quick & easy, you can use a 555 timer, 100uH inductor, MOSFET and a few other parts to build a cheapie supply.
     
  4. hrstar24

    Thread Starter Active Member

    Apr 7, 2009
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    Thanks guys, got a pretty simple boost converter designed.

    Now I was wondering if you guys know of any good simple 12 V regulators? I am using a 12 V battery, but want a regulator for precautionary measures after it. Can anyone link something that I could by on Sparkfun or a similar website?
     
  5. SgtWookie

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    Precautionary measures? Like what, if you turned the car's lights off and a load dump occurred?
     
  6. colinb

    Active Member

    Jun 15, 2011
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    Do you want regulation to 12.0 V so that at full charge, or while being charged, the voltage supplied to your device is not greater than 12.0 V? Then you could use a simple low-dropout linear regulator (LDO) for this. It will give good efficiency because you won't be dropping the voltage very much.
     
  7. #12

    Expert

    Nov 30, 2010
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    Without knowing how much current you will need, the rest is guesswork. Pleas tell how much current to get better answers.
     
  8. hrstar24

    Thread Starter Active Member

    Apr 7, 2009
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    I only need 150 mA out of the circuit. I want a 12 V regulator so if the battery voltage decreases, the voltage is still around 12 V
     
  9. SgtWookie

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    You're going to need a switching regulator circuit then. Not even LDO regulators can output 12v with a 12v input.
     
  10. hrstar24

    Thread Starter Active Member

    Apr 7, 2009
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    Would a zener / transistor circuit work?
     
  11. SgtWookie

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    With that type of regulator, 12v in = 11.3v out, tops.

    You need something like a SEPIC switching regulator topology.

    If you go on National Semiconductors' site, you can use their online simulator to check out various designs. It'll probably take around a dozen parts (regulator IC, a couple of inductors, caps, resistors, etc) to build an appropriate and efficient one.
     
    Last edited: Oct 20, 2011
  12. colinb

    Active Member

    Jun 15, 2011
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    You could get only 0.1 V dropout from a really good LDO. That means if you let the battery voltage drop to only 12 V, then you could get 11.9 V out.

    For instance the TI TPS73801. But it seems hard to get ahold of. However, look at the TPS73801 data sheet Figure 1 (top-left of page 6). You can see the outstanding dropout voltage for your 150 mA current at room temperature. Dropout voltage increases with temperature, but this LDO still performs well.

    Or you could use a switching regulator as Sgt. said and you can have more control of the output. It will cost a little more and/or be more difficult to implement (depending on how much integration you decide on: you can use a complete switcher module, an IC with integrated FET switch but requiring external inductor, or a controller IC requiring external switch FET and inductor).

    EDIT: I wrote “Look at the TI (formerly National) Simple Switcher.”, but ideally you want a converter that can produce output less than, equal to, or greater than its input like SEPIC or buck-boost, and SIMPLE SWITCHER doesn't do that AIUI.
     
    Last edited: Oct 20, 2011
  13. colinb

    Active Member

    Jun 15, 2011
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    Oh, yeah, Sgt. pointed out you need a voltage up- and down-converter if you really want constant 12 V from down to 12 V input.

    SgtWookie: That means SEPIC would work, but could buck-boost work too? Why would you choose one over the other in this case?
     
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