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Electronic Design
Bob’s Mailbox: CCFL Lights, Old Radios, And The 108A

Bob’s Mailbox: CCFL Lights, Old Radios, And The 108A


I just read your latest column and also the special issue of Electronic Design (May 5, 2011) on new lighting technologies. Once again I saw the statement in the article on page 30 (“LED Lighting Moves Closer To The Mass Market”) that “The DoE estimates that if everyone converted to solid-state lighting, then by 2020, enough electricity would be saved to power 32 million homes.”

Yes, indeed, solid-state or CCFL lighting is more efficient and thus generates less heat. But this leads me to the obvious question of where this extra heat goes. Is it really totally wasted as apparently everyone is assuming? Well, I live in the Pacific Northwest and you live in San Francisco. For all but about two weeks each year, the good old inefficient tungsten lamps help us heat the house. \\[Yes, we noticed that. I agree with you completely. /rap\\] And the roughly two weeks of extra warm weather are in the summer when the days are long and the lights are not on all that much anyway. So where is this dramatic savings in energy? \\[Nowhere near you or me. /rap\\]

If forced to convert to non-tungsten lighting, I will just have to run the furnace to compensate. Of course, if you live in Miami the situation is different and the air conditioner has to run extra to remove the heat generated by the lights. \\[You are quite right. /rap\\] But shouldn’t someone be looking at this data more carefully instead of making wild estimates of how much we will save based only on the efficiency of the light sources? The tungsten lamp is a very benign device. It contains no poisonous materials and is cheap to produce with simple materials such as class and common metals.

\\[I have many incandescent lights that are used 1/10 or 1/4 or 1/50 an hour per week. Some idiots have decided that we ought to buy CFLs to put in those places. Well, screw them! I have carefully bought about 80 95-W bulbs to use there so I don’t have to buy CFLs with a return on investment of 0.05% per year! /rap\\]

Solid-state lights contain all kinds of electronics and exotic materials. Are we really going to make the gains that are being touted? For those of us living in temperate climates, I have great doubts that the promised savings will materialize. For me in Seattle, I don’t expect to see any noticeable gains at all. I would be interested to hear your thoughts on this along with other Floobydust stuff.

- Aris Silzars

I think many engineers understand this, even if people don’t. So let me set this aside for a while. Of course you are right. Beast regrds. /rap

Hi Bob:

I used to tinker with car radios as a kid (see “Bob’s Mailbox: Hydraulic Rams, Old Car Radios, And 5-MHz Power” at One of the first radios I owned was an old Buick radio that was given to me as a box of parts. Someone thought I could use the parts to do electronic experiments but I reassembled the radio and it worked!

You mentioned that the vibrator circuit produced 90 V for the tubes. Although 90 V was a common B+ voltage for battery radios with a B battery, the typical voltage out of a vibrator-transofrmer-rectifier was on the order of 200 to 300 V.

Vibrator converters were not used just in car radios. Farm radios for rural areas without utility power often ran from a 6-V source and used a vibrator converter for the tubes. One of the problems that had to be dealt with in these radios is that the 6 V was used to heat the filaments of the tubes and was at the negative end of the B supply. The cathode of the rectifier was at the positive end of the B supply.

Most rectifiers did not have indirectly heated cathodes. The type 80 rectifier had a 5-V filament that was used as the cathode. Although indirectly heated rectifiers were sometimes used, two other rectification systems were also used. One was the cold cathode gas tube rectifier, typically the 0Z4, and the other was synchronous rectification. Synchronous rectification was achieved by an additional set of high-voltage contacts on the vibrator that connected the alternate ends of the transformer winding to the load in synchronism with the ac waveform generated by the low-voltage contacts.

Interestingly enough, most vibrators interrupted the current in the driving coil by shorting the coil instead of breaking the connection to the source. I suppose this was to reduce contact erosion due to arcing, but it did result in a fairly high current draw.

I only encountered one vibrator that broke the connection instead of shorting the coil, and that vibrator was in a battery-powered portable that used the vibrator instead of a B battery. It ran on eight D cells in series parallel to produce 6 V.

I’ve rambled on long enough though, strangely enough, I now work at designing switching power converters and have been since 1960.

- Bruce Wilkinson

Hi, Bruce. Thanks for the stories. Yeah, I never studied any of that stuff. Beast regrds! /rap

Hello Bob:

I have an old design that uses a 108A op amp in a comparator circuit to provide voltage and current feedback for servos. The part is no longer available. I am trying to find an equivalent part but there are very few parts out there that have the 108A low input bias current of 3 nA.

- Kevin Vetter

There may easily be good ICs that will do that, depending on the conditions. What temp range do you have to cover? What supplies? ±15 V? What’s wrong with an LF411A? It has much less lb than 3 nA unless you go above 85°C. This is a classical problem, but in most cases the solutions are easy. The LF411 is pin-compatible. Tell me more about your circuit. I bet the solution is easy. Beast regrds! /rap

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