Retrotechtacular: Understanding a voltage doubler


This very stern looking gentleman is about to explain how voltage doubles work in a plodding, yet satisfyingly thorough manner.

We’re not certain when this US Air Training Command video was produced. Obviously it was used to train servicemen who were responsible for keeping electronics running during war time. We’re glad for that, as they really found just the right balance to present a concept that required some knowledge, but is approachable for even the most basic of new electronics hackers.

The demonstration board shown on the right is the voltage circuit highlighted in the lesson. Here the pointing stick is being used to trace out the circuit function during one phase of the input transformer. The capacitor/diode pairs rectify the voltage, with the capacitors discharging in parallel series to double the output voltage. But how does the variable load (RL) affect the output? This is demonstrated under several different conditions using an oscilloscope to illustrate the change.

The discussion of how the diodes work reminded us of a modern tutorial we just ran across this weekend. It’s a bit bizarre, but explains the PN junction in a different way than we’re accustomed to. In this case you will already need to be familiar with how semiconductors work to understand the presentation.

Both clips can be found below the jump.

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Making a 12V bulb work in a 6V socket


This is something of a square peg in a round hole type of problem. [Kiel Lydestad] has been riding a vintage Moped around. You know, a motorcycle that can be pedaled like a bike. He of course wants to keep the thing looking stock, but also needs it to be fully functional. Enter this light bulb replacement project. His brake light needed a new bulb, and he managed to make this 12V LED bulb work in the 6V socket.

An LED is a really great choice for this application since the Motobécane Moped uses a magneto generator to power the lights. It won’t pull much current, but it did need modification to run from half as much voltage. [Kiel] mentions that it may have been possible to crack open the LED tower and adjust the current limiting circuit inside, but he felt it was easier to just add this voltage doubling circuit. He assembled the components in a way that still allows them to fit in the metal base of the bulb.


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