[sdiy] power-question

[Brown David]

28V doesn't sound unreasonable.  The '18V' winding on the transformer should
produce 18V rms or 25.5V peak, possibly more as the '18V' may be a little
conservative.  My Formant PSU uses a transformer with two 17V secondaries to
generate +/-15V.  The voltage at the bridge rectifier output(i.e. across the
smoothing capacitor)is about 25V under low load.

The power dissipated by your regulator will be the voltage dropped X the
current drawn.  In the Formant, the +/-15V and +5V supplies each use a 723
regulator to drive a 2N3055 power transistor.  So it is the transistors, not
the regulators that dissipates the power.  These don't get hot because
they're mounted on a hefty heatsinks and the synth doesn't draw large
currents.



-----Original Message-----
From: ulrich kehrer [mailto:martin-ulrich.kehrer at ufg.ac.at]
Sent: 05 June 2001 01:05
To: synth-diy at node12b53.a2000.nl
Subject: [sdiy] power-question


hi!

a power supply problem...

i have a 2x18V/2.22A tansformer and after the bridge rectifier i get +/-
28V thus my +/-15V regulators get really hot (i know that the input of
the regulator should only be 3V higher than its output)
i suppose the 28V are not normal, are they?

(the rectifier is a 50V/6A one; i replaced it with 4 1N4005 diodes but
that didn't change anything)

any help concerning the +/-28V is really appreciated.

regards,
ulrich
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