Hi,
I am using a buck converter to obtain a negative voltage, but I have not been successful. I saw a video on YouTube in which the input terminals were interchanged (+ and -), but even after trying that, it still did not work.
Hi Hasham
Most buck converters of the cheaper kind have a common negative or ground. In this case you will not be able to connect the output for a negative voltage.
You will have to find a converter with an isolated negative connection.
Would be an advantage if you quoted the type of converter you are trying to use. Mind reading is not a favourite past time
Cheers Bob
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Hi Bob,
Thanks for your reply. I am using
Yes, you are right checked it has common negative (-In) and ground (-Out).
Two questions
- What sort of load do you need ? e.g. how many amps at what voltage.
- Is the circuit you want to power isolated from everything else… e.g. no common ground needed?
In theory voltages are relative, but how well simple things will work will need to be checked.
e.g. If you take a 0 - 24 Volt and put thew a voltage divider then use the mid point as ground (for the output side), the +24 v now looks like +12V and the ground now looks like -12V… But voltage dividers tend not to be ideal.
e.g. If the Resistor values chosen are two low, you will just be sinking power to ground and wasting it… If the values are too high you may not get enough power to power what you need…
BUT: the real catch is the circuits you connect, are like adding resistance in parallel, thus changing the the “resistance” thus change the voltages.
In some simple circuits it can work, but more compex, not ideal.
The other big catch with this, if your target circuit also connects to something, eg RS232, then the common ground will be connection to 0V on yours which will look like 12V on the other device… not good.
I think I have seen the above referenced as a virtual ground..
On the other hand, Im sure some ready made chips might do it for you… e.g. from a quick google
But you will need to ensure what ever you get meets your needs. I cant recommend an actual product, so this is just an example
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Hi Michael
There are lots of supplies where you input a voltage source and get an output of + v, -v and ground in various forms.
Hasham is delightfully vague when it comes to actual requirements, that is entirely non existent.
If hey thinks to provide some information along his requirements he might just get some results
There are several ways to “roll your own” including a “virtual ground” often used in single supply audio applications. As you say the 2 equal value resistor solution can work for µA currents but a few µF is usually required across each resistor. If a few more mA is requires an op amp configured as a unity gain voltage follower can be used to supply the extra ground current. Still limited by the opAmp current limitations but does provide a low impedance ground point which is the better method.
As you go up in current requirements it gets to the use of isolated buck converters, dedicated devices that supply +/- outputs from a single source or a dedicated +/- power source. This could be a transformer with 2 secondary windings with each winding having its own rectifier bridge with electro capacitor which in effect providing 2 power supplies which can be connected in series with the centre being ground and a +/- supply either side.
But with the present state of zero information regarding requirements the expected query result I think could only be nothing. I suppose some clairvoyance might help but I am not in that business.
Cheers Bob
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Hello all,
I have not tried this, however could you stack 2 buck converters set to the same voltage with the centre - and + connected together as the common 0V point. Top to be + bottom to be -.
Good luck.
Regards
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Hi Bryan
Don’t try it.
To do this you need the buck converter to have isolated negative voltage point to be isolated between input and output or completely separate input supplies and keep input negatives separated. Can get very messy as if this is required the input supply would probably be common, ie; only 1 supply.
If you look closely with non isolated negative points the bottom converter has a short circuit directly across it’s output.
Cheers Bob
Add on
If you were using batteries you could power each buck converter separately with an 18650 2S configuration (4 18650 cells).
BUT the 2 batteries MUST REMAIN SEPARATE. That is 1 X 2S combination MUST be SEPARATE from the other and REMAIN SO.
So to answer your specific question NO !!
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Yes, it was a little tounge in cheek not much thought. With a single supply and some icl76xx series ic’s it can be done.
Apologies.
Hi Bryan
Nothing to apologise for. You just asked a question. I could have just said NO but I thought a bit of a diagram and explanation was in order.
Yes. There are a number of these chips around. I imagine there still are but there used to be available small blocks either PCB mount or fly leads that accept an input voltage range and output +/- Volts fixed. +/- 5V is pretty common. Some were quite high wattage as I remember.
the next step up if you need higher current would be a dedicated 240VAC to +/- XVDC supply.
The buck converters will work if the negative input and output connections are isolated. I think these are available and would be a simple solution
Cheers Bob
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