“Even a blind hog finds an acorn now and then.” Quoted by my boss B.O. Austin and I’m sure many others before him.

The quotation applied to me on many occasions when B.O. assigned me a job that I knew absolutely nothing about or where to start looking for answer. Nevertheless I usually rooted around until I found an answer somewhere. I’ll try to tell of the biggest and juiciest acorn this hog found. It happened years after B.O. retired.

Joe Urish was working on a d-c to a-c power converter for military aircraft. The prototype worked fine, but it had one disturbing deficiency. Under certain load conditions the output voltage became distorted so that it didn’t meet the specifications. One day Joe came to talk about the problem, wondering if I had any ideas. 

“You might use a bigger filter,” I suggested, “but that would increase the weight.”

“Yeah, we’re near the limit already,” said Joe.

“I don’t know what we can do to fix it, but I’ll think on it,” I said.

The means for making alternating current from a direct current source is a digital scheme whereby the load receiving power is connected to the source for a time, then switched to reverse the polarity for a time, and so on, thus generating a series of alternate positive and negative pulses to the load. By varying the duration of the pulses, an a-c voltage can be generated having the desired properties. A filter provides a buffer between the raw pulses and the desired output voltage.

If the switching occurred at the precise times as designed, Joe’s problem would not exist. Unfortunately it takes time for a switch to respond to a command. Response time can vary for several reasons. The main culprit is the magnitude of current in the switch. The cause being identified, what can we do about it?

I scratched my head; rooting around in my brain and anywhere else I could think of for a possible solution. I couldn’t find an obvious answer. After a few days it occurred to me that if I could adjust the control signal depending on the load, I could whip this thing. Finally I stumbled across the obvious.

I could measure the time it takes for the switch to respond to a command, and use the data to modify the control signal, which it repeats periodically. In essence, each switching time delay is put into a memory until the cycle is repeated. Then it is used to cause the control signal to operate sooner than normal, thus compensating for the switching delay, and generating an acceptable output voltage, independent of the load.

Since this control method was found to be useful in other even more important jobs, it was committed to a single integrated chip dubbed the Jessee Circuit. I recon this turned out to be my biggest and best acorn.