Saturday, 8 September 2012

Hans Camenzind tribute

I'd like to share a few pictures taken from my current electronics file.It's one of those big ring-binders like you use at work. I've lost the original one I started 25 years ago when I first picked up a silicon chip, it had many many more similar scribbles to the one below. The 555 and then closely followed by the 741 were the 1st chips I got to play with, next came the 4017, 4011, CA3130 (that's a CMOS 741) and many more. But without the ubiquitous 555 none of this would have happened. My thanks to Hans Camenzind.
Hans Camenzind, Father of the NE555, Dies at the Age of 78
Walton Cocroft-esque voltage doubler using 555.
Annotated 1st page of the Fairchild datasheet (Signetics were the first manufacturer of the 555)

It took me a moment to sketch up the rough outline of a voltage regulator (down-buck) I build in 1986 at school. It relies on the really fast 555 chips' switching speed to saturate a bank of 4 parallel connected 2n3055s. I matched the 2n3055s to run in parallel for equal dissipation which took about a day to temperature test. (This involves wirring 4 transistors up in a test circuit and seeing which ones get hottest, keep those to one side. Repeat with some other transistors, until you have 4 with pretty similar gain characteristics for a set load.) They drive a choke in switched mode, and OK I used a zener and an LM741 as well in the enable circuit to turn the oscillator on and off when the output falls. I cannot remember what frequency I had the 555 at, sorry. It did have a 12Amp 12V transformer, and was able to provide really smooth regulation for 0-12v at up to about 5 amps. It would still control a 10Amp short circuiting load cleanly, so long as the switching noise was not a concern. This circuit was mounted in a Hamrads enclosure and was used in a school lab to charge lead-acid batteries, and even double as a battery on account it was able to run cool even under heavy loads provided by student abuse. The 4 2n3055's in a bank bank are never in the area between on and off for long, and thus they never dissipate much heat.

(Not my original diagram from 1986, I lost that)
A note to anyone doing this at home, the output smoothing cap needs to be about 2000 uf, and you probably want a lot of small ones in parallel to make the value up, because they do get hot.

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