One of my all-time favorite circuits is the the following DC-to-AC inverter (click diagram to enlarge) based on an old color TV flyback:
Transformers made for powering large neon signs are inexpensive and very reliable. Most commonly, the secondary is center-tapped, which prevents the use of its full peak-to-peak output in applications where one of the terminals needs to be grounded.
In the power supply described in this post, I took out the high-voltage transformer out of its metallic enclosure to isolate the center tap from ground. This requires very careful application of a thick insulated layer to the transformer. I used a full can of Shellac to patiently coat and re-coat the transformer. Continue reading
High voltage DC power supplies are used by science enthusiasts for powering electron tubes and x-ray tubes, charging high-voltage capacitors, powering electrostatic “levitators”, etc. Many of these power supplies use a flyback transformer to produce high voltage at high frequency (AC), followed by a “Cockroft-Walton Multiplier” to rectify and dramatically increase the voltage.
The Cockroft-Walton multiplier uses a cascaded series of diodes and capacitors to generate a high voltage DC potential from an AC input through a circuit topology that uses diodes to charge capacitors in parallel and discharge them in series. The output polarity of the Cockroft-Walton multiplier depends on the way in which its diodes are oriented, so the output polarity (referenced to ground) of a high-voltage DC power supply is usually set during the design.
However, since some of our physics experiments require one or the other polarity, we build our Cockroft-Walton multipliers with an extra capacitor so that we can make our HV power supplies output either positive or negative high voltage referenced to ground. Continue reading
The book’s Figure 32 shows the schematic diagram for a low-cost, variable-voltage PMT power supply based on a BXA-12579 inverter module that is originally designed as a power supply for cold-cathode fluorescent lamps. This under-$20 module produces 1,500VAC at around 30kHz from a 12VDC input.
We are posting this picture to help you build your own power supply. It shows the BXA-12579 that has been modified as described in the book. The op-amp to the right of the CCFL module is used to control the voltage supplied to the module. The high-voltage AC output of the inverter is rectified and doubled and filtered by the diodes and capacitors at the left of the CCFL module. Continue reading
We are posting this picture to help you construct the variable-output, low-ripple, high-stability, high-voltage power supply described in pages 38-40 of “Exploring Quantum Physics Through Hands-On Projects.” The schematic diagrams for this power supply are in the book’s Figure 31. Output voltage (up to 2 kV) and current (up to 1 mA) are monitored via two LCD panel meters. Continue reading