Tuesday, March 26, 2013

Adjustable Lab Power Supply - take two :)

So, the previous article about lab power supply gathered quite a interest which is not a big surprise considering that there are over 200 pages of discussions in two topics about the schematic in this forum: http://www.electronics-lab.com/forum/index.php?board=2.0!

I think that the schematic in www.electronics-lab.com is not the original one but a modification of an older schematic published in a Czech electronic magazine. I found it here: http://paja-trb.cz/konstrukce/zdroj.html  There are scanned pages from the magazine with the original article and eagle files for the project.

Wednesday, March 13, 2013

Two versions of soft start

My new project is something that is useful when creating power amplifier with toroidal transformer. Usually the starting (inrush) current is very high for a brief moment until the smoothing capacitors are charged. This is stressful for the capacitors, bridge rectifiers and the transformer itself. Also the fuse may blow.
The soft start circuit is used to limit the starting current to acceptable level. This is achieved by connecting the transformer to the mains via a resistor which is shorted with relay contacts a few moments later.

I decided to combine a soft start schematic with push button toggle switch schematic to create a module ready to be used in a power amplifier or some other power consumer.

I experimented with two different schematics - one with CMOS logic 4027 and other with dual timer NE556.