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jippie
jippie
4:50 AM
morning
 
W5VO
W5VO
5:22 AM
mornin
 
jippie
jippie
6:09 AM
I have some 12V and 14V power supplies that I want to turn into +/-6V (or +/-7V) power supply. Pretty straightforward with a couple transistors and a voltage reference. The challenge though is the maximum current (couple amps) that would dissipate lots of power in the transistors.
Is there a common solution for this, pretty much like a boost/buck-converter, but for a virtual middle rail?
A simple 6V (or 7V) regulator won't do the job as it can source current, but it cant sink current (or prove me wrong).
I guess it is called a "rail splitter circuit", but searching for that only gives me hits on the well known analog/discrete solution that potentially dissipates a lot of power.
 
abdullah kahraman
abdullah kahraman
6:24 AM
@jippie Interesting
 
jippie
jippie
@abdullahkahraman I know, so what is the answer? :-p
Best circuit I found so far is:
 
abdullah kahraman
abdullah kahraman
@jippie The first thing comes to my mind is switcher + ldo
 
jippie
jippie
Would need bit of fiddling because its rest current is only about 30mA and again with higher currents it dissipates a lot of power.
@abdullahkahraman A standard switcher, to the best of my knowledge, can't sink current.
 
abdullah kahraman
abdullah kahraman
@jippie Why would it need to sink current?
Buck–boost converter
The buck–boost converter is a type of DC-to-DC converter that has an output voltage magnitude that is either greater than or less than the input voltage magnitude. It is equivalent to a flyback converter using a single inductor instead of a transformer. Two different topologies are called buck–boost converter. Both of them can produce a range of output voltages, from an output voltage much larger (in absolute magnitude) than the input voltage, down to almost zero. The inverting topology The output voltage is of the opposite polarity than the input. This is a switched-mode power supply with a similar...
 
jippie
jippie
@abdullahkahraman Because that is my design requirement :-p
 
abdullah kahraman
abdullah kahraman
6:28 AM
@jippie lol
@jippie Well, I don't have much info on negative supplies, but a negative supply supplies current in the opposite direction and that is called sinking current right?
 
jippie
jippie
I want to be able to power a 6V load between Either rail and virtual ground, and I want it to cope with unbalanced loads.
 
abdullah kahraman
abdullah kahraman
@jippie Well, so make one +6V converter and then make one -6V converter..
 
jippie
jippie
@abdullahkahraman A load from +12V to +6V (virtual ground). Then the virtual ground is sinking current.
@abdullahkahraman When the load is between +6V (virtual ground) and 0V, the 6V rail is sourcing current.
 
abdullah kahraman
abdullah kahraman
@jippie But that is when you create a virtual ground isn't it?
Anyways don't take my advice serious I am a noob on this subject lol
 
jippie
jippie
@abdullahkahraman I can't connect them into a single virtual ground node, can I. I wouldn't be able to predict the output voltage exactly and therefore both converters will feed the other.
 
abdullah kahraman
abdullah kahraman
6:33 AM
@jippie Oh, yes =)
 
 
10 hours later…
The Photon
The Photon
4:13 PM
@jippie There are switching regulators that produce split rail outputs. I'm pretty sure they're mostly isolated topologies, and IIRC the regulation is generally not so good on one of the outputs compared to the other. Unfortunately I'm not remembering the name for the circuit at the momemnt.
A little searching says that flyback is one type that can be made this way.
But anyway adding a whole separate switching converter stage is probably not what you want.
 
 
2 hours later…
jippie
jippie
5:52 PM
@ThePhoton I have a box full of power supplies, but none of them have a middle rail. I want a middle rail to experiment a bit. For low power the circuit I posted above will do, but anything above approx. 30 mA middle rail current will release the magic blue smoke (if my top of head calculations are correct).
 
 
4 hours later…
W5VO
W5VO
10:15 PM
@jippie Use an op-amp to drive the virtual ground
 

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