Monday, November 20, 2017

Battery-powered boost converter for neon glow lamp

I'm working on a battery-powered DC-DC boost converter for neon glow lamps. It's a switched-mode booster with a 9-volt battery providing input power. The output needs to be at least 90 volts or so, with a current draw in the range of 10 μA to 1 mA. For the target application I also need it to be very quiet below 1 MHz. These constraints (relatively high voltage, very low current, high frequency) puts it in an unusual corner of design-parameter space where I haven't found any ICs (integrated circuits) for sale.

So I'm rolling my own that will ultimately use a CMOS 555 timer (LMC or TLC) as a switch. I'm working my way up in frequency and am currently using a standard NE555. I've been breadboarding square-wave oscillators to compare the recommended datasheet configuration to some alternatives. The other night I felt lucky and skipped ahead and quickly implemented the rest of the booster using an available MPSA42 "high voltage" NPN BJT, a 4.7 mH axial inductor with unknown stray capacitance and self-resonance frequency and a neon glow lamp as the load. Here's the result:
Neon glow lamp DC-DC boost converter MkI. It's beautiful to me!

Close up with NE555 DIP-8 IC on the left and TO-92 MPSA42 BJT to its east-southeast. To the left of the glow lamp is an oversized black diode, with the green inductor behind it and the brown filter capacitor behind its anode lead.

And zoomed out: no cheating, the 9V battery is the only power source
So I passed the first milestone: I am powering a neon glow lamp with a 9V battery! The open-circuit output voltage was 120V. The good performance of the MPSA42 transistor was a positive surprise. It probably wasn't intended for power supplies, but I'll keep it at least for the next few design iterations. However, getting the operating frequency above a megahertz will require some effort. While I'm waiting for promising inductors to arrive (hopefully with low enough stray capacitance), I'm doing circuit simulations with ngspice, but that's another post.

Friday, November 17, 2017

Calling computers names in Swedish

I wrote a correction to the very nice article "Carl-Gustaf Rossby: Theorist, institution builder, bon vivant". Rossby and Germund Dahlquist developed a numerical weather model for the BESK computer in 1953-54 and the article made the erroneous claim that "Rossby pursued numerical weather prediction in Sweden in an era in which there was no Swedish word for digital computer". I listed the five Swedish terms for digital computer that were in use at the time. My purpose was not to nitpick, but to make the point that Stockholm in 1953 might well have been uniquely fertile soil for developing novel applications for computational science because of BESK and Dahlquist.

Through luck and skill, Sweden managed to stay out of WWII and had a booming, technologically advanced, industrial economy in the post-war period. In 1947 the Swedish government initiated attempts to buy a computer from the US. A Swedish delegation of five young engineers got remarkable access to the principals behind the early computers in the US. However, ultimately the Swedish government was denied an export license for a US computer and BESK was rapidly designed and built in Stockholm (at my alma mater KTH) using know-how gained during the visit to the US. BESK became operational in September 1953 and was briefly the fastest computer in the world, capable of 16,000 additions per second. It was also the first computer to (partially) use semiconductor electronics (400 germanium diodes).

The Swedish government's primary need for a computer was to support their nuclear-weapon program, which could explain the denied US export license, and to decrypt intercepted Russian radio communication. The ability to decrypt all electronic communication between Berlin and the German embassy in Stockholm had been instrumental in keeping Sweden out of WWII. Continued access to encrypted Russian diplomatic and military radio communications to help navigate the cold-war political environment was a strong motivation.

In stark contrast to this political and military pragmatism was Dahlquist's scientific idealism. His goal was to disperse rigorous computation through all fields of science and technology. Together with co-author Åke Björck he wrote the world's first textbook on numerical methods, with an emphasis on numerical accuracy and stability. Dahlquist's collaboration with Rossby on numerical weather modeling was one of the main achievements of this quest. Their work enabled 24-hour national weather forecast in Sweden from September 1954, 4-5 years earlier than in any other part of the world. Rossby's decision to return to Sweden from the US in 1953 to pursue weather modeling on computers was a wise one, not the folly of trying to do state-of-the-art computing in a place that did not yet have a word for computer.