+/-18V & +48V from a battery

[jeppix]

Hello to everybody!

I will try some solutions, in fact my preamp project is based on two pcb; one is the preamp circuit for both chanel and the other will be the power supply so I could test.

If someone find out other solution please tell me and I try

Thanks

[sivan_and]

white LED boost regulators based on Inductors..that what i meant !!!

[Cliff45]

Hello all-

Have you thought about the fact that you may not actually need a true 48VDC for the microphone you're using to actually work properly? Many very high-end units use a phantom voltage well below the 48V standard and work just fine. I have run Schoeps CMC6 microphones and AKG 414-TLII mics on 12VDC phantom power without issues. Like was previously said here, not every microphone uses phantom power for the same things, some just use it as a capsule bias voltage, and others use if for this and to power a built-in preamplifier or FET buffer circuit. These that have built-in circuitry almost always need higher voltage or current. You should have a look at the spec sheets for the mics you'll be using with this preamp, maybe you don't need a voltage above 18VDC at all.

Many portable mixers like the Shure FP-33 have switchable phantom power voltages, either 12V or 48V. They do this with just two standard 9V batteries in series, and this gives you about 6 hrs. battery life even when powering three microphones from it.

Maybe the Shure FP-33 schematics would be worth a look? I don't know if it's available from Shure, I didn't see it on their website.....

HTH

[monter]

Maybe try this: http://www.monterdiy.vel.pl/?p=118

Phantom step-up converter can by made on LM2577
http://www.national.com/ds/LM/LM1577.pdf

My schematic I add soon, it's simple. 9V battery supply, and 50V on output.

[Eva]

Most of the ICs mentioned are completely unsuitable due to the high quiescent current.

Another alternative is to use a PIC with ADC to control three separate boost and flyback regulators, that may operate in "pulse skip" mode to get better efficiency. This avoids the transformer but requires three independent MOSFET and inductors and some programming skills.

Capacitance of 9V alkaline batteries seems to be in the 400mAh range.

[star882]

How about use a small lead acid battery instead?

[Conrad Hoffman]

Up conversion isn't terribly efficient if the ratio is high, especially if you raise the frequency so you can use smaller components. It can be noisy. The layout is sensitive. The lower the current draw the less the efficiency because it's hard to reduce quiescent consumption below a certain point. Efficiency with a boost converter, maybe 85% if you do everything perfectly. Efficiency with a group of batteries in series, 100%. Don't cut the 48V phantom by too much. Though mics will work on much less, they don't all perform as well as they do at the specified voltage. IMO, a lot of the negative comments I've read on the inexpensive large diaphragm condenser mics now available are a result of running them at reduced voltages.

[monter]

http://www.moxtone.com/ostalo.htm

With standard condenser microphone (current about 3mA) 9V lithum battery works about 8 hours.

My portable phantom 48V supply:

[Electrone]

Originally posted by jeppix
Hello to everybody!

I will try some solutions, in fact my preamp project is based on two pcb; one is the preamp circuit for both chanel and the other will be the power supply so I could test.

If someone find out other solution please tell me and I try

Thanks

The way I would do it is to use a 74C14 (CD40106) in a 16 pin DIP package. It has low quiesent current ratings. It can drive some small signal coupling transformers. The transformers are wound with a lot of fine wire. They have a lot of inductance and about 50 ohms of resistance per winding. They should be quiet for conducted noise. They might need some mechanical shielding.

Here is the basic idea.

[Electrone]

The filter capacitors should be bigger than those shown. I used those small values for simulation purposes. I think 47uF is a good value for each one.