While the original purpose for the supply was a lowish cost replacement for larger analogue mixing consoles it can also be used for many other uses where +/- 17 volts (other voltages can be set) and +48 volts is required such as 500 and 51x style racks (although 2 boards will be needed, one for the +/-16V and 48V supplies and the second to deliver the +/-24V rails)
The supply uses switching regulators, with buck regulators for the +/- supplies and a boost regulator to generate the 48 volt supply. This keeps the regulator efficent and means a readily available Dual 25 Volt transformer may be used.
While specifications ultimately depend on the Transformer and heat-sinking used, the power supply is capable of delivering:
+17V at 5 Amps
- 17V at 5 Amps
+48V at 1 Amp
Circuit description
This circuit is based
around Texas Instruments LM2585 and LM2679 simple switchers regulators, I
did consider using linear regulators, but that approach would have ended
up generating up to 200W of heat, (or almost as much power as the supply
delivers). Using switching regulators dropped power dissipation to a much
more manageable 16 Watts.
There are two basic Switchers in use here, IC1 and IC21 act as buck
regulators, while IC11 is a boost regulator generating the 48V supply.
They are configured to run off a 21- 40 Volt input, so a readily available
dual 25 Volt transformer may be used.
Following feedback from the
small desk supply project, I elected to make this supply trimmable with a
range covering 13-18 Volts which should cover the common supply voltages,
typically 15V, 16V and 17V.
As the Switchmode integrated circuits
used in this supply have a fast rise time, this can result in some ringing
on the output with a fundamental around 30-35Mhz, as this is well above
Audio frequencies it is not expected to cause any issues, however the
secondary filters of L2, C101, C102 etc. are adequate to deal with this
noise.
If this noise is an issue, the power supply needs to be mounted
in an earthed metal box with ferrites placed around any input and output
leads. As this is intended as an external supply I would expect this to be
mounted in a metal case anyway, but is still worth mentioning
here.
I chose the LM2679 over the LM2678 as it has soft start
capability, so it should be able to start with a highly capacitive load.
Having said this though, tests with the LM2678 found that it happily
started even with 15,000uF across it.
I would not expect that any
mixing consoles would have any issues with the soft-start, however I have
not tested every desk out there, so it may be safer to assemble the power
supply with soft-start disabled by leaving off C4 and C24 and only fitting
them if soft-start is required (i.e. if the power supply struggles to
start under load.
heading 2
test
Kit costs $xx (Australian) and
includes:
PCB
Assembly
instructions
Email
for more details or Paypal instructions (to order) - note at this stage I
will have to work out mail costs on a case by case
basis...
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