Power supplies
 

On Fri, 20 Jan 2006 04:31:26 GMT, "U-Know-Who"
wrote:

+
+"james" wrote in message
...
+ On 19 Jan 2006 13:39:54 -0800, "Professor"
+ wrote:
+
++James is certainly right... if you plan to draw much current from your
++supply... you may have make other arrangements then just dropping all
++that voltage. That thing will be a real furnace.
++
++Professor
++www.telstar-electronics.com
+ *****
+
+ I was once thinking of using a transformer that had a secondary
+ voltage of 36VAC and use pass transistors I had in my spare box. I
+ wanted to use a T0-220 case NPN and the design required the use of 8
+ of them in order to lower the heat dissapation per transistor. That
+ changed my mind and ended up usign a different transformer.
+
+ james
+
+Usually, transformers can be found more reasonably priced than
+semiconductors of high current ratings, especially surplus!
+
******

I am well aware of that. I picked up a nice transformer for $10 once.
4200 VAC CT at 2 amps intermmittant secondary. The transformer was one
cubic foot and weighed 85 lbs.

If you know where the surplus shops are, transformers and power supply
parts can be had for realtively cheap prices.

james

Power supplies
 

james wrote:
On Thu, 19 Jan 2006 02:12:09 -0500, Scott in Baltimore
wrote:


+Any suggestions for regulators that will handle a max 48 volt
+VCC?. I have 3 transformers that output 35 VAC at a few amps.
+I'd like to build some 13.8 VDC supplies. Seems 723's and 317's
+are maxxed at 40 volts. I see 317HV's that are good to a VCC
+of 60 volts. The large pass transistors from PC power supplies
+are good for 10 amps and the smaller ones make good buffers.
+Each stage drops .7 volts, so maybe I can go back to the old
+zener diode/resistor regulator trick. A buffer and output would
+give a final 13.6 volts.

****

Are any of them center tapped secondaries?


No. I may be dumping these transformers.


man dropping around 35 volts across any regualtor or pass transistor
is going to require a good size heat sink with any appreciable current
draw. Three amps and you are dropping about 100+ Watts across any
regulator or pass transistor(s).


Just pulling a few amps with a 25 volt VCC generates a lot of heat.


With center tapped secondaries you can run a fullwave center tap
rectifier setup and are looking at upwards to 25 VDC out into a
capacitor input filter. About 16 VDC with a choke input filter. There
your regualtor or pass transistor wil not have as much voltage drop
across them. The heat sink size is reduce considerably.


I know, I know...

Power supplies
 

On Fri, 20 Jan 2006 10:52:50 -0500, Scott in Baltimore
wrote:

+james wrote:
+ On Thu, 19 Jan 2006 02:12:09 -0500, Scott in Baltimore
+ wrote:
+
+
++Any suggestions for regulators that will handle a max 48 volt
++VCC?. I have 3 transformers that output 35 VAC at a few amps.
++I'd like to build some 13.8 VDC supplies. Seems 723's and 317's
++are maxxed at 40 volts. I see 317HV's that are good to a VCC
++of 60 volts. The large pass transistors from PC power supplies
++are good for 10 amps and the smaller ones make good buffers.
++Each stage drops .7 volts, so maybe I can go back to the old
++zener diode/resistor regulator trick. A buffer and output would
++give a final 13.6 volts.
+
+ ****
+
+ Are any of them center tapped secondaries?
+
+
+No. I may be dumping these transformers.
+
+
*****

If they have enough current rating, they maybe usefull for a 40VDC
supply to power a 100 to 250 watt amp?


james

Power supplies
 

+No. I may be dumping these transformers.
+
+

*****

If they have enough current rating, they maybe usefull for a 40VDC
supply to power a 100 to 250 watt amp?

After I made a dimmer using some of these transistors, I realized I had created
a high current DC amp, so I applied half voltage (bias) and fed a capacitor coupled
AC input to the base and took a capacitor coupled AC output from the emitter
and now I can amplify audio. I made a duplicate of the first, and now I have
a stereo class A audio amp. I might take those transformers and create an unregulated
40+ volts DC to power this amp. I need to redesign the input circuit...

Makes some heat with a 13.3 volt VCC. You need to draw some current from the
transistors to develop a decent voltage drop to get clear audio. I'm using
light bulbs as high wattage resistor. I had to make two separate bias adjusts
or it would have ended up monophonic.

It's a FrankenAMP! (TM)

Can I make class AB by making splitters on toroids like is done for RF amps?
I only have large NPN transistors. I've got a lot of them, and quite a few
old computer power supplies for resistors and capacitors.

Power supplies
 

Scottiekins being gay in Baltimore wrote:
Any suggestions for regulators that will handle a max 48 volt
VCC?. I have 3 transformers that output 35 VAC at a few amps.
I'd like to build some 13.8 VDC supplies. Seems 723's and 317's
are maxxed at 40 volts. I see 317HV's that are good to a VCC
of 60 volts. The large pass transistors from PC power supplies
are good for 10 amps and the smaller ones make good buffers.
Each stage drops .7 volts, so maybe I can go back to the old
zener diode/resistor regulator trick. A buffer and output would
give a final 13.6 volts.

Anyone who would even consider doing that is a total idiot.

Power supplies
 

On Sun, 22 Jan 2006 14:55:33 -0500, Scott in Baltimore
wrote in
:

+No. I may be dumping these transformers.
+
+

*****

If they have enough current rating, they maybe usefull for a 40VDC
supply to power a 100 to 250 watt amp?

After I made a dimmer using some of these transistors, I realized I had created
a high current DC amp, so I applied half voltage (bias) and fed a capacitor coupled
AC input to the base and took a capacitor coupled AC output from the emitter
and now I can amplify audio. I made a duplicate of the first, and now I have
a stereo class A audio amp. I might take those transformers and create an unregulated
40+ volts DC to power this amp. I need to redesign the input circuit...


Just put a small variac on the line side. You can pick up one on ebay
for peanuts. In fact, I've got a Staco 501 that I'll sell you for $20
plus shipping.


snip
Can I make class AB by making splitters on toroids like is done for RF amps?
I only have large NPN transistors. I've got a lot of them, and quite a few
old computer power supplies for resistors and capacitors.


Yes, the transformer-coupled push-pull audio amp is a fundamental
circuit. The only issue is that an output transformer is required
which limits the fidelity of the amp. That, and you'll probably have
to wind your own output transformer. You could also try a totem-pole
variation -- you need an input transformer with two secondaries (or
some other way of floating the base bias supply), and a really big
capacitor instead of an output transformer. If you use a bipolar
supply you might even be able to eliminate the capacitor.








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