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Getting negative voltage from single battery source

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bacteria

New Member
My electronics skills are very basic to say the least. I can just about follow a basic electronics diagram but a lot of it baffles me; and let's face it, electronics is far to easy to launch into technical workings and geek-speak and baffle the "novice"!

My hobby is making video gaming consoles into portable handheld systems, or, as a forthcoming project, an integrated multi-system; which involves board reductions, modding boards, etc.

In other words, i'm an intelligent chappie, however my electronics knowledge is extremely basic (although I am very good at fine soldering work). We all have strenths and weaknesses, so please be gentle!!

So, here's my application for request of your help please: One of my console systems is a ColecoVision console, which annoyingly requires not only 12v but also 5v and -5v. The 12v is easy (might even run of 7.4v Li-ions maybe) and the 5v I can easily get off a 7805 or a step-down regulator like the PTH08000 series. Problem is the -5v (negative). I need (as memory serves me) around 200mA on -5v, so ideally wanting to have the ability for 500mA on -5v. I will be using the same power supply for the 12v or 7.4v (7.4v ideally), 5v, 3.3v (for another application) and this -5v.

I have tried a couple of options already and failed. I have found this Negatron converter **broken link removed** which seems ok (I think!) although quite expensive.

I am hoping there is an easy way to do this, and some kind soul here could show a really easy to follow diagram for someone with limited electronics know-how to follow please? Ideally a sketch with pictures or easy diagram?

I read somewhere here that people sometimes use two battery supplies, one for positive voltages and the other for negative voltages. How can that work when it means in effect having grounding also being connected to the positive terminal on a negative voltage system too (eg like the Coleco example above) - surely that will cause a short??


**broken link removed** **broken link removed**
 

crutschow

Well-Known Member
Most Helpful Member
You certainly can use two batteries. The battery for the positive voltage has it's negative terminal grounded, and the battery for the negative voltage has its positive terminal grounded. No short.
 

Hero999

Banned
You need a buck-boost converter.

There are plenty of ICs that can do this, check out the Linear Technology, Maximum and National Semiconductor websites.

As you're running from a battery, it's probably also a good idea to use a buck switching regulator to get the 5V from the battery because it's more efficient than the LM7805.
 

bacteria

New Member
That's good to know and certainly an option; thanks for that; however, if it were possible to achieve the negative voltage easily along with the positive voltages using one battery source it would be better as all the cells can then be recharged together rather than having to use two sets. (if there is no easy method though, will have to consider two battery sources).

Not heard of a "buck switching regulator" before. I tend to use PTH08000 as they are variable between 1.9v and 5v, run at about 93% efficiency (I think that's right if memory serves me) and about 1.5 amps. 7805 are fine for low amperage needs, they aren't too efficient and need heatsinks as get rather hot otherwise. I was kinda hoping there to be an existing pre-made and cheap component for converting plus to minus (then use a 7905 to convert).

Please provide links and more importantly an easy to follow diagram of using them, I have looked on many PDF files and frankly, find them mega confusing, I like "connect X to Y" type stuff!!
 

Boncuk

New Member

bacteria

New Member
Would this item be what I want - "1V ~ 5V to USB 5V 500mA Inverter Board" on ebay, **broken link removed**

**broken link removed**

I was wondering as the item is USB so designed 5v by the looks of it; I presume "Inverter" means will take 5v in and output -5v out. Is this right?
 

tcmtech

Banned
Most Helpful Member
If your negative voltage power requirements are fairly low a simple charge pump circuit using a 555 timer or similar does pretty well.

Its still a fairly common concept on many small electronics IC's that have single sources but still need a small negative voltage source of one sorts or another.
 
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