About how to discover and cure parasitic oscillations, here in a 2 transistor HV Darlington supply

Please read the description/textbox. In this video I show how to find out in a “hands-on” way where a parasitic oscillation in an electronic circuit is present and how to cure it (at least: in this case).

We are talking about a 110 V DC power supply that has to give out a variable voltage/current between 0 and 110 V, made with two HV transistors. Correction: of course (2.58 in the vid.) the output voltage comes out of the emitter (!) so not the collector.

Warning/disclaimer (!): Video is not made for children or people with no experience in electronics. Never touch with your bare hands a DC or AC 110 Volt power supply, it is dangerous and can be lethal in some cases. And (important) the circuit is not ideal, even with this solution there is a faint hum/oscillation (?) in cases of maximum output current via a power resistor. Not when the power resistor is bridged with a wire. Anyway: a useful but not ideal circuit. The Tektronix analog 66 MC scope shows a faint hum, the digital Chinese scope Hantek DSO 5202P does not show it.

Use for test purposes the setup that I show in this video: take a 100 N (=0,1 uF) 350 V AC capacitor between your fingers and touch the circuit with the end-tip of that capacitor.

At the same time: look at the oscilloscope and see what happens.

And/or: use 2 crocodile clip wires, clip the 0,1 uF 350 V capacitor in-between, clip one to the mass/minus of the circuit and touch, with the other well isolated crocodile clip the different points in the 110 Volt (electronic) circuit. And look what happens on the scope.

It is the second video regarding parasitic oscillations. I now show the way how to find them and show 1 case of curing them.

The principles about finding them are showed. These principles can be used to detect where faults/flaws in a circuit and thus to make electronic circuits working better or repair them.

Relevant earlier “parasitic oscillations video” (26 February 2022) is here https://youtu.be/bSxKoh_1Wy0

Much earlier videos of the past year:

First VLOG about this power supply on 5 may 2021 https://youtu.be/WMNrqqHwufo

Second VLOG about this Power supply on 5 may 2021 is here https://youtu.be/fusQIrGtALo

Part 3 basic setup of this power supply https://youtu.be/URpAQYbWHjQ

Another part about this power supply https://youtu.be/uVVH9h3MHQs
Voltage doubler of this power supply (can be used everywhere) https://youtu.be/PQ7Tamffv9w
Heat control tips of this power supply https://youtu.be/3N9dpRfPh0k
Pop out AC fuse detection circuit https://youtu.be/Pam963MnRX8

Please note: first experiments during the past year were with a Power MOSFET. It started to oscillate always, due to its high input impedance on its Gate.

That MOSFET setup thus makes it extremely vulnerable for sloppy wiring.

The S2000A (old school driver transistor in analog TV circuits, originally driving the HV coil of an analog TV set on say 16 KC) or the BUV 47 R (say the same application) and the BUT 11 AF (driver) are High Voltage Silicon NPN transistors that can withstand the heat/dissipation.

Datasheets are on the www. Their Hfe amplification factor is very low (!) say between 5 and 10 or 15. That is normal in these cases. Important: that was tested with a normal transistor tester, not one specified to test HV transistors…

The end-transistor must be mounted on a very large heatsink, visible in the first video, because of its DC drive.

The driver (BUT 11 AF) needs a moderate heatsink. Preferred: a separate one for the BUT 11 AF driver because the end-transistor must not heat-up the driver transistor. That is a kind of common law.

When you have questions about (certain analog) electronic circuits and how to make them: go to my Channel trailer (Radiofun232 on You Tube) and go to the “looking glass”. Type there the electronic keywords that you want/need.

My You Tube channel trailer is here: https://youtu.be/xbgQ8T3oqh4 When you search, search always “NEWEST FIRST” to get the right overview. You can also search via the “looking glass” on my Channel trailer via keywords like ”audio”, “radio”, “amplifier”, “filter”, “Shortwave”, “transistor”, “FET”, “oscillator”, “generator”, “switch”, “schmitt trigger” etc; so the electronic subject you are interested in. My books about electronics & analog radio technology are available via the website of "LULU”, search for author “Ko Tilman” there.
https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=Ko+Tilman

I keep all my YT videos actual, so the original video’s with the most recent information are always on YouTube. Search there, and avoid my circuits that are republished, re-arranged, re-edited on other websites, giving not probable re-wiring, etc. Some persons try to find gold via my circuits. I take distance from all these fake claims. I cannot help that these things happen. Upload 1 March 2022.