Power Sources
1. Miniature DC–DC Converter
The LM3909 was originally designed as an LED flasher, but has many other applications. One that I’ve enjoyed experimenting with is a miniature power supply that allows a tiny watch battery to power a neon lamp or even a powerful semiconductor-laser pulser. Both these applications require 70 to 150 volts at relatively low current.
Figure A shows the circuit of the LM3909 dc-dc converter. In operation, the LM3909 rapidly switches Q1 on and off at a rate determined by C1. The transistor can be considered a switch in series with choke L1 and resistor R2. Each time Q1 switches off, the magnetic field set up by the current flowing through L1 collapses and induces a high voltage across the inductor. ...
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