Generating 48V@50mA from 5V for microphone phantom power...

[Jaye Gallagher]

Hi there,

I need to generate a fairly clean 48V at around 50mA to be used for phantom
power for up to four microphones. The source voltage I need to step up
somehow is the 5V output of a battery driven DC-DC step up. Whilst I've
looked around for parts and schematics for this, any help or comments would
be much appreciated.

Thanks,
Jaye.

 

[John Woodgate]

I read in sci.electronics.design that Jaye Gallagher
2park-reader-02.sydney.pipenetworks.com.au>) about 'Generating 48V@50mA
from 5V for microphone phantom power...', on Tue, 28 Dec 2004:

I need to generate a fairly clean 48V at around 50mA to be used for
phantom power for up to four microphones. The source voltage I need to
step up somehow is the 5V output of a battery driven DC-DC step up.
Whilst I've looked around for parts and schematics for this, any help or
comments would be much appreciated.

If your 5 V-48 V converter were 100% efficient, you would draw 480 mA
from your battery. Can you supply a current significantly larger than
that?

 

[Jaye Gallagher]

I read in sci.electronics.design that Jaye Gallagher
2park-reader-02.sydney.pipenetworks.com.au>) about 'Generating
48V@50mA from 5V for microphone phantom power...', on Tue, 28 Dec
2004:


If your 5 V-48 V converter were 100% efficient, you would draw 480 mA
from your battery. Can you supply a current significantly larger than
that?

Hmm. You're right, that's a lot. Perhaps I'm confused about the amount of
power required for a single phantom power supply? I've seen phantom power
supplies that claim to power a mic. for 10-30 hours from 2 AA batteries. (Or
thought I had in my net trawling.)

I haven't been able to find any hard specs on the current that should be
available via phantom power. Anyone have any idea?

Thanks,
Jaye.

 

[Jaye Gallagher]

Hmm. You're right, that's a lot. Perhaps I'm confused about the
amount of power required for a single phantom power supply? I've seen
phantom power supplies that claim to power a mic. for 10-30 hours
from 2 AA batteries. (Or thought I had in my net trawling.)

I haven't been able to find any hard specs on the current that should
be available via phantom power. Anyone have any idea?

Have just trawled around a bit more. Seems that 2mA per mic. is a more
reasonable estimate of the average current drawn by professional condenser
microphones. Some draw more, some less (see
http://www.sounddevices.com/tech/phantom.htm).

So, let's say that I want a supply circuit that can set up +5V to +48V and
provide probably around 10mA in total, but have capacity to provide up to
50mA (if the end-user plugs in power hungry microphones, that's their
business).

Thanks,
Jaye.

 

[Rich Grise]

Hi there,

I need to generate a fairly clean 48V at around 50mA to be used for phantom
power for up to four microphones. The source voltage I need to step up
somehow is the 5V output of a battery driven DC-DC step up. Whilst I've
looked around for parts and schematics for this, any help or comments would
be much appreciated.

As long as you already have batteries, just get 5X 9V "transistor radio"
batteries and clip them in series. Voila! 45V painlessly! If 45V isn't
enough, 6 in series will give you 54V, which you could regulate down
to 48.

Good Luck!
Rich

 

[Jaye Gallagher]

As long as you already have batteries, just get 5X 9V "transistor
radio" batteries and clip them in series. Voila! 45V painlessly! If
45V isn't enough, 6 in series will give you 54V, which you could
regulate down
to 48.

Good Luck!
Rich

Well, I'm hoping to use a single battery source for this device, as it's
supposed to be portable. Hence the requirement that the 48V be derived from
my existing 5V supply.

Thanks anyway, though,
Jaye.

 

[John Woodgate]

I read in sci.electronics.design that Jaye Gallagher
2park-reader-02.sydney.pipenetworks.com.au>) about 'Generating 48V@50mA
from 5V for microphone phantom power...', on Tue, 28 Dec 2004:

Hmm. You're right, that's a lot. Perhaps I'm confused about the amount of
power required for a single phantom power supply? I've seen phantom power
supplies that claim to power a mic. for 10-30 hours from 2 AA batteries. (Or
thought I had in my net trawling.)

That may refer to powering simple electret microphones that draw less
than 1 mA.

I haven't been able to find any hard specs on the current that should be
available via phantom power. Anyone have any idea?

The famous IEC/EN 61938, Table 11. Specification 48 V +/- 4V, maximum
current 10 mA (per microphone). Typically, the 48 V supply is fed to the
microphone via two 6.8 kohm resistors that are effectively in parallel.
Many microphones do not draw as much as 10 mA. but some do.

There is a significant problem with phantom supplies, even in some
mixing desks, that have inadequate current capacity. Also, there are two
lower voltage supplies standardized in IEC 61938 Table 11:

12 V +/- 1 V, maximum current 15 mA;
24 V +/- 4 V, maximum current 10 mA.

The 24 V standard is no longer used, it appears, by any microphone
manufacturer.

 

[John Woodgate]

I read in sci.electronics.design that Jaye Gallagher
2park-reader-02.sydney.pipenetworks.com.au>) about 'Generating 48V@50mA
from 5V for microphone phantom power...', on Tue, 28 Dec 2004:

Well, I'm hoping to use a single battery source for this device, as it's
supposed to be portable. Hence the requirement that the 48V be derived
from my existing 5V supply.

But what is your actual *battery* voltage? It can't be 5 V. If you run
your 48 V converter directly from the battery you will get a much higher
efficiency overall.

 

[Jaye Gallagher]

But what is your actual *battery* voltage? It can't be 5 V. If you run
your 48 V converter directly from the battery you will get a much
higher efficiency overall.

Oh, if I could find a way to step the battery voltage (2.4V, two NiMh cells)
up to 48V, that'd be ideal, but all of the parts I've looked at so far seem
to have around 5V minimum input voltages.

Jaye.

 

[martin griffith]

Hi there,

I need to generate a fairly clean 48V at around 50mA to be used for phantom
power for up to four microphones. The source voltage I need to step up
somehow is the 5V output of a battery driven DC-DC step up. Whilst I've
looked around for parts and schematics for this, any help or comments would
be much appreciated.

Thanks,
Jaye.

the feeble phantom, bottom of the page
http://www.rycote.com/information/default.htm
gives a lot of P48 info




martin

Serious error.
All shortcuts have disappeared.
Screen. Mind. Both are blank.

 

[John Woodgate]

I read in sci.electronics.design that Jaye Gallagher
2park-reader-02.sydney.pipenetworks.com.au>) about 'Generating 48V@50mA
from 5V for microphone phantom power...', on Tue, 28 Dec 2004:

Oh, if I could find a way to step the battery voltage (2.4V, two NiMh cells)
up to 48V, that'd be ideal, but all of the parts I've looked at so far seem
to have around 5V minimum input voltages.

Oh, if you are starting from 2.4V, you have a REAL BIG problem. Have you
considered social work as a career? (;-)

 

[martin griffith]

I read in sci.electronics.design that Jaye Gallagher
2park-reader-02.sydney.pipenetworks.com.au>) about 'Generating 48V@50mA
from 5V for microphone phantom power...', on Tue, 28 Dec 2004:
Oh, if you are starting from 2.4V, you have a REAL BIG problem. Have you
considered social work as a career? (;-)

2.4v will be a problem, but some people use PP3's and still get next
to no life out of them
http://www.canford.co.uk/commerce/productdetails.aspx?productid=20-752
quote
"providing at least 5 hours life (at 2 x5mA microphone current) from
an alkaline battery."

That is a miserable performance. Have a long lunch break, and you have
lost your P48!


martin

Serious error.
All shortcuts have disappeared.
Screen. Mind. Both are blank.

 

[Sharptop]

I think you need to be a little tighter on your design spec. But in any
case
here is a component that can step up 3.1 volts to 48V
http://www.national.com/pf/LM/LM5000.html

 

[Tim Wescott]

Hi there,

I need to generate a fairly clean 48V at around 50mA to be used for phantom
power for up to four microphones. The source voltage I need to step up
somehow is the 5V output of a battery driven DC-DC step up. Whilst I've
looked around for parts and schematics for this, any help or comments would
be much appreciated.

Thanks,
Jaye.

Why pay the efficiency hit twice, one on the 5V switcher and one on the
phantom power supply? Why not just power the phantom supply straight
from the batteries?

 

[Tim Wescott]

Jaye Gallagher wrote:




Have just trawled around a bit more. Seems that 2mA per mic. is a more
reasonable estimate of the average current drawn by professional condenser
microphones. Some draw more, some less (see
http://www.sounddevices.com/tech/phantom.htm).

So, let's say that I want a supply circuit that can set up +5V to +48V and
provide probably around 10mA in total, but have capacity to provide up to
50mA (if the end-user plugs in power hungry microphones, that's their
business).

Thanks,
Jaye.

You can certainly do this, but you'll pay a cost in efficiency,
component cost and size -- a switching power supply takes a certain
standing power whether it's delivering power or not, and that standing
power generally increases as the design power output of the switcher
goes up. In addition you'll need larger, more expensive magnetics and
semiconductors to implement the thing for 2.5W instead of 0.5W -- but
requirements is requirements.

 

[Tim Wescott]

John Woodgate wrote:




Oh, if I could find a way to step the battery voltage (2.4V, two NiMh cells)
up to 48V, that'd be ideal, but all of the parts I've looked at so far seem
to have around 5V minimum input voltages.

Jaye.

Check for a chip that'll let you power the chip from 5V (small drain)
and your power section from 1.8V at 1.4A (two NiMh cells in the middle
of the discharge knee) or 2.0V (two NiMh cells on the leading edge of
the discharge knee).

Where do you get your D-size NiMh cells?

 

[Ben Bradley]

I read in sci.electronics.design that Jaye Gallagher
2park-reader-02.sydney.pipenetworks.com.au>) about 'Generating 48V@50mA
from 5V for microphone phantom power...', on Tue, 28 Dec 2004:

Gee, that's lots of lines of attribution. Keep reading, my original
content is further down...

That may refer to powering simple electret microphones that draw less
than 1 mA.

And that's different from the phantom power standard, it's usually
called "bias power" and is used for electret condenser mics plugged
into soundcards and minidisc recorders with their 1/8" miniphone
connectors, as well as in built-in mics for telephone answering
machines.

The famous IEC/EN 61938, Table 11. Specification 48 V +/- 4V, maximum
current 10 mA (per microphone). Typically, the 48 V supply is fed to the
microphone via two 6.8 kohm resistors that are effectively in parallel.
Many microphones do not draw as much as 10 mA. but some do.

A few microphones may have a center-tapped transformer output,
which would effectively ground both resistors (these of course should
not have phantom power applied, but that's another topic). This would
give 14mA per microphone, or 42mA total if three such microphones are
plugged in (thus the OP's 50mA spec isn't too far off for absolute
worst-case conditions). Also, each of these 6.8k's will be dissipating
0.34 watts with the full 48V across them, so it's a good idea to use
1/2W resistors.

There is a significant problem with phantom supplies, even in some
mixing desks, that have inadequate current capacity. Also, there are two
lower voltage supplies standardized in IEC 61938 Table 11:

12 V +/- 1 V, maximum current 15 mA;
24 V +/- 4 V, maximum current 10 mA.

The 24 V standard is no longer used, it appears, by any microphone
manufacturer.

Some mics are designed to work over the 12V to 48V range, but there
may be lower performance at 12V.

 

[John Woodgate]

I read in sci.electronics.design that Ben Bradley <ben_nospam_bradley@mi
ndspring.com> wrote (in <[email protected]>)
about 'Generating 48V@50mA from 5V for microphone phantom power...', on
Tue, 28 Dec 2004:

And that's different from the phantom power standard, it's usually
called "bias power" and is used for electret condenser mics plugged into
soundcards and minidisc recorders with their 1/8" miniphone connectors,
as well as in built-in mics for telephone answering machines.

No-one claimed that it was the same as *standardized* 48 V phantom
power. Some such mics are powered on the unbalanced signal conductor,
some have 'A-B' phantom power.

 

[John Woodgate]

I read in sci.electronics.design that Tim Wescott
com>) about 'Generating 48V@50mA from 5V for microphone phantom
power...', on Tue, 28 Dec 2004:

Where do you get your D-size NiMh cells?

I think 'Flag' size cells would be better!

 

[Allan Herriman]

A few microphones may have a center-tapped transformer output,
which would effectively ground both resistors (these of course should
not have phantom power applied, but that's another topic). This would
give 14mA per microphone, or 42mA total if three such microphones are
plugged in (thus the OP's 50mA spec isn't too far off for absolute
worst-case conditions). Also, each of these 6.8k's will be dissipating
0.34 watts with the full 48V across them, so it's a good idea to use
1/2W resistors.

It's possibly a bad idea to use 1/2W resistors, as these aren't
usually available in the close tolerances required. The match (but
not the actual value) of the two resistances needs to be very
accurate.

It is possible to make up the desired power rating by using a number
of lower powered precision resistors in parallel or series.

Regards,
Allan