9v to 48vdc dc/dc converter or 48v switcher power supply needed

[Jon Erickson]

Im designing a microphone preamplifier and in the interest of size and
affordability I am turning away from the linear power supply and
searching for a 9vdc to 48vdc dc/dc converter or an AC to 48v
switchmode supply. I know that there are supplies and converters now
that operate in the high megahertz and are fine for audio. The
current draw of the amplifier is around around 100 ma total. Does
anyobody have any suggestions of where to look for these?

Jon

 

[MM]

Im designing a microphone preamplifier and in the interest of size and
affordability I am turning away from the linear power supply and
searching for a 9vdc to 48vdc dc/dc converter or an AC to 48v
switchmode supply. I know that there are supplies and converters now
that operate in the high megahertz and are fine for audio. The
current draw of the amplifier is around around 100 ma total. Does
anyobody have any suggestions of where to look for these?

Jon

Jon,

I tried emailing you directly but it bounced back.

Is this for commercial purposes or for hobby? I have a design of such a
DC/DC switcher, which however has not been tested. I was working on a
similar project but had to put it aside... In my design I was trying to
minimize switching noise, so I used an IC with controlled rise time. It is
however is not the most efficient approach. The simplest way to go is to use
the National web based design software
http://www.national.com/appinfo/power/webench/. It might be good enough...

/Mikhail
/mi so ma at rogers com/ (put it all together by deleting spaces and adding
a dot)

 

[Tim Shoppa]

Im designing a microphone preamplifier and in the interest of size and
affordability I am turning away from the linear power supply and
searching for a 9vdc to 48vdc dc/dc converter or an AC to 48v
switchmode supply. I know that there are supplies and converters now
that operate in the high megahertz and are fine for audio. The
current draw of the amplifier is around around 100 ma total. Does
anyobody have any suggestions of where to look for these?

Are you sure you have the current right? 48 V * 100 mA = 4.8 watts.
That's a lot of power for a microphone preamp.

If the current drain is really in the low milliamps, switched-capacitor
(e.g. voltage multiplier) converters are quite reasonable (although
I usually see them operated in below the MHz range).

Tim.

 

[John Woodgate]

I read in sci.electronics.design that Tim Shoppa <shoppa@trailing-
edge.com> wrote (in <[email protected]>)
about '9v to 48vdc dc/dc converter or 48v switcher power supply needed',

Are you sure you have the current right? 48 V * 100 mA = 4.8 watts.
That's a lot of power for a microphone preamp.

48 V suggests that the preamp can supply phantom power to capacitor
microphones.

 

[Tim Shoppa]

I read in sci.electronics.design that Tim Shoppa <shoppa@trailing-
edge.com> wrote (in <[email protected]>)
about '9v to 48vdc dc/dc converter or 48v switcher power supply needed',


48 V suggests that the preamp can supply phantom power to capacitor
microphones.

At a current drain of zero mA .

While 48V preamps aren't necessarily designed for efficiency, I cannot
imagine that it needs 100mA.

Tim.

 

[John Woodgate]

I read in sci.electronics.design that Tim Shoppa <shoppa@trailing-
edge.com> wrote (in <[email protected]>)
about '9v to 48vdc dc/dc converter or 48v switcher power supply needed',

At a current drain of zero mA .

While 48V preamps aren't necessarily designed for efficiency, I cannot
imagine that it needs 100mA.

IEC 61938 specifies 10 mA per channel for 48 V phantom power. The OP
doesn't say he has more than one channel, but that's not relevant if we
believe he knows what current he wants. 100 mA could be right for an
8-channel unit.

 

[Lee]

Im designing a microphone preamplifier and in the interest of size and
affordability I am turning away from the linear power supply and
searching for a 9vdc to 48vdc dc/dc converter or an AC to 48v
switchmode supply. I know that there are supplies and converters now
that operate in the high megahertz and are fine for audio. The
current draw of the amplifier is around around 100 ma total. Does
anyobody have any suggestions of where to look for these?

Jon

Jon,

I have used Linear Tech's LTC1871 in SEPIC configuration. Input
voltage was a tad higer at 12V, but got decent performance (noise was
less than 5mVP-P at 580kHz, less than that below that.) It was hard
pressed to deliver 100mA due to duty cycle limitations. This part
might suit you...

Lee

 

[budgie]

Im designing a microphone preamplifier and in the interest of size and
affordability I am turning away from the linear power supply and
searching for a 9vdc to 48vdc dc/dc converter or an AC to 48v
switchmode supply. I know that there are supplies and converters now
that operate in the high megahertz and are fine for audio. The
current draw of the amplifier is around around 100 ma total. Does
anyobody have any suggestions of where to look for these?

You said "size and affordability" in the same sentence as "9vdc". I hope your
9vdc source isn't a normal PP3 style 9v battery. 100mA at 48v =4.8W before
conversion losses. A 9v battery is going to suffer meltdown looking at that
load.

If that ISN'T the battery you are choosing, why not go for a 12v gel cell.

Then again, I'm likely jumping at shadows. You probably already have a 9vdc
power supply.

 

[Robert C Monsen]

Im designing a microphone preamplifier and in the interest of size and
affordability I am turning away from the linear power supply and
searching for a 9vdc to 48vdc dc/dc converter or an AC to 48v
switchmode supply. I know that there are supplies and converters now
that operate in the high megahertz and are fine for audio. The
current draw of the amplifier is around around 100 ma total. Does
anyobody have any suggestions of where to look for these?

Jon

If you download the SWCad III tool from linear, it has a nifty option that
will allow you to pick one of linear's switcher chips, given an input and
output voltage specification. It will then show you a circuit using it, and
the waveform you are likely to expect given the load.

I just ran it using input = 8-12, output = 48V, output current = 0.1, and
came up with 9 chips that you could use, all of which do better than 80%
efficiency.

Regards,
Bob Monsen