Dual supplies

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Dual supplies

Postby Viewmaster » Mon Oct 24, 2016 5:13 pm

I have +5v from a laptop and wished to get -5v for dual supplies.

Have found and ordered a volts converter 7660 which is just an 8 pin device and only needs
2 external C's to work. It can deliver -5v at 20 m/a with only a 1/2 v drop.

Haven't yet tried it but it seems an easy and cheap way to get a low current dual supply.

It can also voltage double and they can also be cascaded too.

Here's the spec..........http://www.ti.com/lit/ds/scas794/scas794.pdf
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Re: Dual supplies

Postby Harry Dalek » Mon Oct 24, 2016 7:14 pm

My thoughts were on a dual supply a week ago i was thinking of this idea but was worried about the oscillator might get picked up in my video circuits .
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Re: Dual supplies

Postby Viewmaster » Mon Oct 24, 2016 9:58 pm

That's a lot of trouble to go to, that circuit, Harry, just to get neg volts from pos.

The 7660 is very cheap and only has 5 connections to make!
(Has a built in osc.) I haven 't read anywhere about osc break thro
but we shall see.

Will let you know when and if it works for me.
Of course I could go the 12v +12v tranny route but using the laptop supply is a new challenge for me.

As is usual here, it's the bloody chip (frying tonight!) side of things (electronic), of my project that is giving me the willies. :D
The mechanics and software are sailing along (albeit in a calmish breeze!)
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Re: Dual supplies

Postby Harry Dalek » Mon Oct 24, 2016 10:13 pm

Viewmaster wrote:That's a lot of trouble to go to, that circuit, Harry, just to get neg volts from pos.

The 7660 is very cheap and only has 5 connections to make!
(Has a built in osc.) I haven 't read anywhere about osc break thro
but we shall see.

Will let you know when and if it works for me.
Of course I could go the 12v +12v tranny route but using the laptop supply is a new challenge for me.

As is usual here, it's the of bloody chip side of things (electronic), of my project that is giving me the willies. :D
The mechanics and software is sailing along (albeit in a calmish breeze!)


Hi Albert ...Yes looks like a good chip just used what i had handy as i wanted a battery supply and was tossing up if i could do away with a battery ,any case i went with the extra battery and clean supply no nasty extra rf circuit to worry about later ...
i will look into getting that chip in the future could come in handy .
Keep at Albert i am trying as well just to take my time and get every thing working .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Dual supplies

Postby Steve Anderson » Tue Oct 25, 2016 6:55 pm

The simplest answer is to use a second battery, unless you have size or weight constraints. Two batteries will last twice as long as one - assuming the load on each is similar, plus you don't have the losses due the conversion/inversion. There's also no chance of conversion ripple rearing its ugly head, and you don't have to build the inverter which requires components and board space - I know not much - but there it is.

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Re: Dual supplies

Postby Harry Dalek » Tue Oct 25, 2016 8:32 pm

Steve Anderson wrote:The simplest answer is to use a second battery, unless you have size or weight constraints. Two batteries will last twice as long as one - assuming the load on each is similar, plus you don't have the losses due the conversion/inversion. There's also no chance of conversion ripple rearing its ugly head, and you don't have to build the inverter which requires components and board space - I know not much - but there it is.

Steve A.


Know much you do as Yoda would say :lol:
I went with a second battery for my idea just for the reasoning ....might not be wise to add a problem of RF when i don't have to .... a battery has none clean and no extra circuit to construct ....perhaps a little more weight but that ok i am strong ! :wink:
A few years from now we will all use super capacitors instead of batteries quick charge lot less weight.... will we bother with a mains supply at all apart from charging them ?.
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Dual supplies

Postby Steve Anderson » Thu Oct 27, 2016 2:25 am

Sometimes the obvious is hidden somehow from reasoning. Even in this case if the loads were not similar on pos and neg supplies you might know that for every neg battery you'l be replacing two positive. Not as 'perfect' as you might like, but it does the job. It's not something I would suggest for a consumer product, but here I would like to think that we're a bit more savvy about these sort of things.

If the batteries were rechargeable then there's even less reason to be concerned.

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Re: Dual supplies

Postby Viewmaster » Thu Oct 27, 2016 3:57 am

Harry here's another little gizmo I have just bought you might find handy some time.

The XL6009 step up board using a LM 2577 chip.
It converts low DC volts up to 30 fully adjustable for any volts required.

I put a 4.5 v battery on it and got over 24v.
It can deliver up to 3amps (heat sink required at high amps)

I am going to try and use it to boost the 5v at .5 amp USB from my laptop

It runs at 50KHz so is well above NBTV freq.

Now for the good news. They are sold on eBay for less that £2 with free posting in UK!

How do they make and sell them so cheaply? Amazing.
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and what was in your father's jeans."
Albert.
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Re: Dual supplies

Postby Harry Dalek » Thu Oct 27, 2016 8:19 am

That sounds good Albert i will look into that .
I only have a small amount of internet at the hotel i am at so can't download or search much but i will look into it when i get home .
UK making ic's sounds good they might start a trend ! :wink:
I am worried about harmonics might wise to look at any harmonics just in case
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Harry Dalek
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