Phantom power from battery

I've seen a clever circuit somewhere that converted the voltage from a 9V battery to 48V using a 555 and a voltage doubler. I need to do something similar but I can't find the circuit now. I don't really need 48V since the mic I'm going to use it with functions on anything from about 18V up. It has to be really small, so ideally it should run with a 1,5V battery but I don't know if that's even possible.

Does anyone have any ideas on this?

Thank you for your help,

Anders

You're on the law of diminishing returns trying to build a voltage multiplier from a 1.5V battery. Almost everything is going against you - diode voltage drops, VM output impedance, battery internal resistance.

I did some work on this problem some while ago and ended up using 12V camera batteries in series. See, for example:http://www.farnell.com/datasheets/7895.pdf or http://www.farnell.com/datasheets/21179.pdf

A pair of these would suit you quite well, and they are probably smaller than an AA and the VM circuitry. At least with this approach you know your battery power is all going into the phantom supply and not being dissipated in the switching components. In addition, you don't have to get rid of the burble from the inverter.

[quote author="kvintus"]I've seen a clever circuit somewhere that converted the voltage from a 9V battery to 48V using a 555 and a voltage doubler. [...] I don't really need 48V since the mic I'm going to use it with functions on anything from about 18V up.[/quote]

Not what you asked for, but how about just using a second 9V battery ? No circuit design needed, and no headaches caused by switching noise. Chances are that, when you add shielding and filtering, a DIY switcher will not be much smaller than a 9V battery.

What are you planning to use this for ?

JDB.

Sony
part # 1-464-758-11
DC - DC converter

is cool for this job
but 9v is on the lower limit for things to work properly but does work

you can buy 48 volt batts.
use a fuse.

The reason I don't want to use two or three 9V (or even one) is the size. The guy I'm building this for wanted it to be built into a 1/2" tube with XLRs in both sides so that it would look a bit like an extension to the microphone. He also wanted to use a standard battery that can be found anywhere. Otherwise the camerabatteries would have been nice and it's likely that I will end up using either those or some 9V standards. I was already guessing that 1,5V is way to low to be useable, since most components have a minimum supply requirement of about 3V.

What are you planning to use this for ?

JDB.

Click to expand...

Phantom power to a microphone :roll: . I think he will use it for some portable measurement system or something like that.


An other idea! Three AAA batteries in series will give us 4,5 V and would probably fit inside the tube. That could be something, right?

/Anders

[quote author="kvintus"][quote author="jdbakker"]What are you planning to use this for ?[/quote]
Phantom power to a microphone :roll: .[/quote]
That bit was clear.
[quote author="kvintus"]I think he will use it for some portable measurement system or something like that.[/quote]
That's why I asked. Is there any way to extract power from that system ?
[quote author="kvintus"]An other idea! Three AAA batteries in series will give us 4,5 V and would probably fit inside the tube. That could be something, right?[/quote]
Yup. Either go with:
- a (7)555 and a simple diode-capacitor voltage doubler (simple but inefficient)
- a Linear Technology LT1073 or similar (available from Digi-Key). The LT1073 data shtte has several design examples, and it's available in SO-8 which is small enough to fit in the tube but large enough to DIY.
- a specialized microcontroller like the ATTiny26L, programmed as a step-up reg. The advantage is that, if you have access to the sampling clock, it is easy to synchronize the switching so that you get minimal noise.

If you can choose between several step-up regulators, pick one without burst mode; burst mode is good for current efficiency but bad for conducted and transmitted noise.

HTH,

JDB
[who is using an ATTiny as a phantom supply for a portable mic pre]

[quote author="jdbakker"][quote author="kvintus"][quote author="jdbakker"]What are you planning to use this for ?[/quote]
Phantom power to a microphone :roll: .[/quote]
That bit was clear.
[/quote]

Sorry. Bad humor...


I don't think there's any practical way to extract power from the measurement system. At least he wasn't keen at all on that idea.

The LT1073 looks interesting (and has a really nice name). I'll look into that a bit more. The microcontroller seems a bit too complicated for me and unless you convince me that it isn't I won't try that route.

Thank you so much for your help!

/Anders

look around for non standard batteries, like a litium cell for a personel electrincs device.
maybe they make em in high volts,small package.

don't complictae 48 vdc with noisy switchers nd other silliness, it ain't worth the time.

I know at the Stores here you can Buy 12v Batteries that are about Half the Size of a AA battery so 2 of these Batteries would Give you 24v and take up the space of one AA Battery and if you used a Voltage doubler you could get close to 48v.....

You could also use a Bunch of 1.5v Watch batteries in series and about 15 of those would use the same space as a AA battery and give you about 20v+......


Cheers

I researched my reply quite carefully before posting links to the data sheets of two types of batteries that could do the job.

Just take a look at the current/life curves of watch batteries. Go on, do the calculations and work out the component losses in voltage-doubler circuits running under these conditions, and then admire the output voltage vs load curves. Read the original post that said the microphone will function from 18V upwards and match that against discharge curves for the different battery types. The LT1073 is a nice device, but using it for this job would entail physically big inductors and there is also no short-circuit protection in step-up mode.

It's a very reasonable question to have asked. The answers are not easy.