48V to 12V@4A DC-DC converter

T

Tim Shoppa

Guest
I need to convert 48V (actually 54V nom. telco battery voltages) to 12V at
4Amps. Isolation isn't needed. I've looked at the NatSemi Simple
Switchers, but the voltages are real near the high end of the "HV" series
(makes me nervous, I don't like to run active devices just a few
volts from their advertised upper limit for extended periods)
and I think the current is out of range of the HV devices anyway.

Can anyone recommend either a device that is appropriate (at these
currents I may need a power MOSFET, I realize, in addition to the
the switching controller) or an off-the-shelf box that does this
conversion?

I should add that the off-the-shelf box has to be under $100 or so. I've
found some telecom suppliers that sell appropriate capacity DC-DC converters
but they seem to start in the $400 range!

Tim.
 
Tim Shoppa wrote:
I need to convert 48V (actually 54V nom. telco battery voltages) to 12V at
4Amps. Isolation isn't needed. I've looked at the NatSemi Simple
Switchers, but the voltages are real near the high end of the "HV" series
(makes me nervous, I don't like to run active devices just a few
volts from their advertised upper limit for extended periods)
and I think the current is out of range of the HV devices anyway.

Can anyone recommend either a device that is appropriate (at these
currents I may need a power MOSFET, I realize, in addition to the
the switching controller) or an off-the-shelf box that does this
conversion?

I should add that the off-the-shelf box has to be under $100 or so. I've
found some telecom suppliers that sell appropriate capacity DC-DC converters
but they seem to start in the $400 range!

Tim.
Click to expand...
If you run a MOSFET switch from the 48V into a buck LC-filter at 50%
duty cycle more or less, open loop with no attempt to regulate, you get
24V more or less- and this brings you within range of the monolithic
switchers- the buck regulators. The step-down can also be considered a
DC transformer so that 4A at 12V translates to 1A at 48V- neglecting
efficiency- and this is not much current. You end up with two inductors
and two power elements, but if it's just a one-of-a-kind, it will be a
simple and fast way to go.
 
I should add that the off-the-shelf box has to be under $100 or so. I've
found some telecom suppliers that sell appropriate capacity DC-DC
converters
but they seem to start in the $400 range!
Click to expand...
Look on the surplus market. I've seen this stuff dirt cheap, because of the
48V input.
 
Fred Bloggs wrote:
Tim Shoppa wrote:

I need to convert 48V (actually 54V nom. telco battery voltages) to
12V at
4Amps. Isolation isn't needed. I've looked at the NatSemi Simple
Switchers, but the voltages are real near the high end of the "HV" series
(makes me nervous, I don't like to run active devices just a few
volts from their advertised upper limit for extended periods)
and I think the current is out of range of the HV devices anyway.

Can anyone recommend either a device that is appropriate (at these
currents I may need a power MOSFET, I realize, in addition to the
the switching controller) or an off-the-shelf box that does this
conversion?

I should add that the off-the-shelf box has to be under $100 or so. I've
found some telecom suppliers that sell appropriate capacity DC-DC
converters
but they seem to start in the $400 range!

Tim.


If you run a MOSFET switch from the 48V into a buck LC-filter at 50%
duty cycle more or less, open loop with no attempt to regulate, you get
24V more or less- and this brings you within range of the monolithic
switchers- the buck regulators. The step-down can also be considered a
DC transformer so that 4A at 12V translates to 1A at 48V- neglecting
efficiency- and this is not much current. You end up with two inductors
and two power elements, but if it's just a one-of-a-kind, it will be a
simple and fast way to go.
Click to expand...
Check the ON Semi MC34063/33063 regulator- this is very flexible, and
the data sheet shows several configurations to boost the current and
input voltage capacity.
 
Why make it

Check out
http://www.meanwell.com/product/SD-50/catalog.gif


JG

"Tim Shoppa" <shoppa@trailing-edge.com> wrote in message
news:bec993c8.0401171724.2461420e@posting.google.com...
I need to convert 48V (actually 54V nom. telco battery voltages) to 12V at
4Amps. Isolation isn't needed. I've looked at the NatSemi Simple
Switchers, but the voltages are real near the high end of the "HV" series
(makes me nervous, I don't like to run active devices just a few
volts from their advertised upper limit for extended periods)
and I think the current is out of range of the HV devices anyway.

Can anyone recommend either a device that is appropriate (at these
currents I may need a power MOSFET, I realize, in addition to the
the switching controller) or an off-the-shelf box that does this
conversion?

I should add that the off-the-shelf box has to be under $100 or so. I've
found some telecom suppliers that sell appropriate capacity DC-DC
converters
but they seem to start in the $400 range!

Tim.
Click to expand...
 
Followups set.

In sci.electronics.components Tim Shoppa <shoppa@trailing-edge.com> wrote:
I need to convert 48V (actually 54V nom. telco battery voltages) to 12V at
4Amps. Isolation isn't needed. [...] I should add that the off-the-shelf
box has to be under $100 or so.
Click to expand...
Mouser has a C&D converter, Mouser part 580-VKA50MS12, 33-75 Vin, 12 Vout
@ 4.2 A, $100 qty 1.

Jameco has a couple of Mean Well power supplies that might work: 212468,
36-72 Vin, 12 Vout @ 8.3 A, $73 qty 1; 212505, 36-72 Vin, 12 Vout @ 4.2 A,
$52 qty 1.

Jameco and All Electronics have some (surplus/used?) 48 V input converters
for less than $20, but the only ones they have right now seem to be 3.3 V
or 5 V out. If you don't mind used, only need a few, and can live with
5 V, that might be a cheap way out.

Standard disclaimers apply; I don't work for any of the companies above.

Possible glitch: aren't telecom supplies usually negative? In other
words, the positive terminal of the battery is grounded. Isolation
might turn out to be important, depending on what you want to do with
it.

Matt Roberds
 
In article <bec993c8.0401171724.2461420e@posting.google.com>,
shoppa@trailing-edge.com mentioned...
I need to convert 48V (actually 54V nom. telco battery voltages) to 12V at
4Amps. Isolation isn't needed. I've looked at the NatSemi Simple
Switchers, but the voltages are real near the high end of the "HV" series
(makes me nervous, I don't like to run active devices just a few
volts from their advertised upper limit for extended periods)
and I think the current is out of range of the HV devices anyway.

Can anyone recommend either a device that is appropriate (at these
currents I may need a power MOSFET, I realize, in addition to the
the switching controller) or an off-the-shelf box that does this
conversion?

I should add that the off-the-shelf box has to be under $100 or so. I've
found some telecom suppliers that sell appropriate capacity DC-DC converters
but they seem to start in the $400 range!

Tim.
Click to expand...
You mean like these? Only fifty bucks if you buy five of them. :)
http://www.mpja.com/productview.asp?product=7725+PS

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Tim Shoppa wrote:
I need to convert 48V (actually 54V nom. telco battery voltages) to 12V at
4Amps. Isolation isn't needed.
Click to expand...
<snip>
I should add that the off-the-shelf box has to be under $100 or so. I've
found some telecom suppliers that sell appropriate capacity DC-DC converters
but they seem to start in the $400 range!

Tim.
Click to expand...
http://www.mpja.com/productview.asp?product=7725+PS

$60. looks like exactly what you need. Good luck!
 
Try ebay, I needed one for my 48 volt golfcart to run 12v lights,radio,ect.
I got a factory 48 to 12v converter rated @ 75 watts constant for $19.00 new.
The seller normally has these in the electronic parts listings most of the time.
 
Fred Bloggs <nospam@nospam.com> wrote in message news:<4009EA25.6040108@nospam.com>...
Tim Shoppa wrote:

I need to convert 48V (actually 54V nom. telco battery voltages) to 12V at
4Amps. Isolation isn't needed.

If you run a MOSFET switch from the 48V into a buck LC-filter at 50%
duty cycle more or less, open loop with no attempt to regulate, you get
24V more or less- and this brings you within range of the monolithic
switchers- the buck regulators. The step-down can also be considered a
DC transformer so that 4A at 12V translates to 1A at 48V- neglecting
efficiency- and this is not much current. You end up with two inductors
and two power elements, but if it's just a one-of-a-kind, it will be a
simple and fast way to go.
Click to expand...
I like that idea. Now lets go a step further and use the same core for
both switchers. Can we do that? I'm trying to picture what happens
IRL.

The on/off switching has to synchronised on both trs, so you can run
them both off the one control section. I'd suggest start up with fixed
frequency until the required 12v is reached at the output, at which
point you either switch to variable frequency, or else just switch
that fixed frequency drive to get you regulation.


BTW there is a simpler approach than all of this, which is one simple
convertor. You could use a fixed frequency fixed m/s ratio drive, and
gate it to regulate the output. All done with one basic opamp IC, a
zener and a tran.


Regards, NT
 
N. Thornton wrote...
BTW there is a simpler approach than all of this, which is one simple
convertor. You could use a fixed frequency fixed m/s ratio drive, and
gate it to regulate the output. All done with one basic opamp IC, a
zener and a tran.
Click to expand...
Given that the 48V input voltage is regulated and the output doesn't
need extreme load regulation, a simple forward converter may be just
what the doctor ordered. Take a half-bridge (one IC plus two FETs)
driving (ac-coupled) a small 4:1 pot-core transformer & a full-wave
rectifier. This may be just what the doctor ordered. There are many
self-oscillating half-bridge FET-driver ICs available, such as IR's
IR2153 and IR21531. I'm sure there are lower-voltage ones as well.
If the IC also has an over-current-sense shutoff, that would be nice.

Thanks,
- Win

whill_at_picovolt-dot-com
 
On 19 Jan 2004 18:17:33 -0800, Winfield Hill
<Winfield_member@newsguy.com> wrote:


Given that the 48V input voltage is regulated ...
Click to expand...
From ETSI EN 300 132-2 V2.1.1 (2003-01):

"The normal service voltage range for the -48 Vdc nominal supply ...
shall be -40,5 Vdc to -57,0 Vdc."

I'm not sure whether this spec applies to the OP's problem, but it
gives an idea of the sort of voltages that -48V equipment must be
designed to tolerate.

Oh, from the same spec:
"Telecommunications equipment operated at -48 Vdc shall not suffer any
damage when subjected to the following voltage ranges:
0,0 Vdc to -40,5 Vdc and
-57,0 Vdc to -60,0 Vdc"

Regards,
Allan.
 
On Tue, 20 Jan 2004 15:23:37 +1100, Allan Herriman
<allan.herriman.hates.spam@ctam.com.au.invalid> wrote:

On 19 Jan 2004 18:17:33 -0800, Winfield Hill
Winfield_member@newsguy.com> wrote:


Given that the 48V input voltage is regulated ...

From ETSI EN 300 132-2 V2.1.1 (2003-01):

"The normal service voltage range for the -48 Vdc nominal supply ...
shall be -40,5 Vdc to -57,0 Vdc."

I'm not sure whether this spec applies to the OP's problem, but it
gives an idea of the sort of voltages that -48V equipment must be
designed to tolerate.

Oh, from the same spec:
"Telecommunications equipment operated at -48 Vdc shall not suffer any
damage when subjected to the following voltage ranges:
0,0 Vdc to -40,5 Vdc and
-57,0 Vdc to -60,0 Vdc"
Click to expand...
That's at "interface A". Internal DC/DC converters will typically get
a little bit less, due to drops in fuses, inrush limiters, filters,
etc.

Regards,
Allan.
 
Allan Herriman <allan.herriman.hates.spam@ctam.com.au.invalid> wrote in message news:<dcfp009cp9gfi6o19unlt5jbifra0sv33d@4ax.com>...
On Tue, 20 Jan 2004 15:23:37 +1100, Allan Herriman
allan.herriman.hates.spam@ctam.com.au.invalid> wrote:
On 19 Jan 2004 18:17:33 -0800, Winfield Hill
Winfield_member@newsguy.com> wrote:

"Telecommunications equipment operated at -48 Vdc shall not suffer any
damage when subjected to the following voltage ranges:
0,0 Vdc to -40,5 Vdc and
-57,0 Vdc to -60,0 Vdc"

That's at "interface A". Internal DC/DC converters will typically get
a little bit less, due to drops in fuses, inrush limiters, filters,
etc.
Click to expand...

Either way, the OP will most likely need regulation. An IC with
current limiting was suggested, but this wouldnt be necessary in the
simple fixed ms ratio switcher using an inductor (rather than
transformer) because the L and fixed ms ratio sets a current limit.
This approach is most simple.


Regards, NT
 
Allan Herriman wrote...
Winfield wrote:

Given that the 48V input voltage is regulated ...

From ETSI EN 300 132-2 V2.1.1 (2003-01):
"The normal service voltage range for the -48 Vdc nominal supply ...
shall be -40,5 Vdc to -57,0 Vdc."

I'm not sure whether this spec applies to the OP's problem, but it
gives an idea of the sort of voltages that -48V equipment must be
designed to tolerate.
Click to expand...
Very good. But perhaps as you say the OP can live with a similar
worst-case variation? At any rate, I was thinking of communications-
equipment racks with dedicated high-quality -48V rack-mount supplies.

Thanks,
- Win

whill_at_picovolt-dot-com
 
Allan Herriman <allan.herriman.hates.spam@ctam.com.au.invalid> wrote in message news:<c0bp00t85ogrk6bag9ucl3t21k8bp84rv9@4ax.com>...
On 19 Jan 2004 18:17:33 -0800, Winfield Hill
Winfield_member@newsguy.com> wrote:


Given that the 48V input voltage is regulated ...

From ETSI EN 300 132-2 V2.1.1 (2003-01):

"The normal service voltage range for the -48 Vdc nominal supply ...
shall be -40,5 Vdc to -57,0 Vdc."

I'm not sure whether this spec applies to the OP's problem, but it
gives an idea of the sort of voltages that -48V equipment must be
designed to tolerate.
Click to expand...
In my case, it's a telco-surplus "-48V" battery backup unit. When
everything is right, the voltage at the terminals is 54.4V (actually
tweaked around there by temperature compensation). Anything much above
that indicates that either the batteries are being grossly overcharged
or have come unhooked from the circuit. When disconnected from
AC power, it drops down to 50V or so, then continues drifting down
as the batteries discharge. Below 40V would be unhealthy for the
batteries, so there's a cutout somewhere in that range (I haven't
purposefully discharged it yet).

The $50 Meanwell supply looks good, now I have to see if Jameco has it
in stock or if I have to wait for it to come over on the next boat...

Tim.
 
On 20 Jan 2004 05:20:23 -0800, shoppa@trailing-edge.com (Tim Shoppa)
wrote:

Allan Herriman <allan.herriman.hates.spam@ctam.com.au.invalid> wrote in message news:<c0bp00t85ogrk6bag9ucl3t21k8bp84rv9@4ax.com>...
On 19 Jan 2004 18:17:33 -0800, Winfield Hill
Winfield_member@newsguy.com> wrote:


Given that the 48V input voltage is regulated ...

From ETSI EN 300 132-2 V2.1.1 (2003-01):

"The normal service voltage range for the -48 Vdc nominal supply ...
shall be -40,5 Vdc to -57,0 Vdc."

I'm not sure whether this spec applies to the OP's problem, but it
gives an idea of the sort of voltages that -48V equipment must be
designed to tolerate.

In my case, it's a telco-surplus "-48V" battery backup unit.
Click to expand...
Ah, good. That makes things simpler. I had assumed that you were
designing equipment for use in a phone exchange.

BTW, that ETSI spec can be downloaded from the ETSI web site:
http://www.etsi.org/services_products/freestandard/home.htm

There should be an equivalent Telcordia spec for Nth. America, but
I've never been able to find it. [If someone knows...]

Regards,
Allan.
 
I need to convert 48V (actually 54V nom. telco battery voltages) to 12V at
4Amps.
Click to expand...
How about $7.95?

meci.com

Input: 36-72 VDC, 1.8 Amp. Output: +12VDC @ 4.2 Amp max., OVP: 13.7-15.7.
Overcurrent: 4.3-5.7 Amp. Model # FPD12-4.2-48. PCB mount. UL, CSA
approved. Includes data sheet.. Mfg: Kepco. Frequency: 500 Khz. 50 Watt. Size: 4.53"
(L) x 2.28" (W) x 0.52" (H)



MFG: KEPCO
Manufacturer Part Number: FPD12-4.2-48
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is busy, hung or dead....................................20915-1433
 
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