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

Thread Starter

hrstar24

Joined Apr 7, 2009
32
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?
 

#12

Joined Nov 30, 2010
18,210
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.
 

SgtWookie

Joined Jul 17, 2007
22,210
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.
 

Thread Starter

hrstar24

Joined Apr 7, 2009
32
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?
 

#12

Joined Nov 30, 2010
18,210
Without knowing how much current you will need, the rest is guesswork. Pleas tell how much current to get better answers.
 

Thread Starter

hrstar24

Joined Apr 7, 2009
32
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
 

SgtWookie

Joined Jul 17, 2007
22,210
Would a zener / transistor circuit work?
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:

colinb

Joined Jun 15, 2011
351
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:

colinb

Joined Jun 15, 2011
351
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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