Рет қаралды 53,171
It's taken me a while to get around to looking at one of these things. It's a compact electronic power supply that takes mains voltage in and puts out a rough equivalent of 12V AC.
I say rough equivalent, because the output consists of a 100/120Hz modulated high frequency hump with spikes in the region of about 30V that average out to 12V as seen by a simple tungsten load.
LED lamps may tolerate being connected to these things, but may suffer damage. I always recommend using 12V DC LED drivers for your 12V LED lamps.
These units will not operate correctly if under-loaded. They require a minimum current to ensure stable oscillator start up on each half wave. If replacing lamps in ceiling lights with LED and they suddenly start flashing and flickering as a group, there's probably one of these involved. The fix is either to replace one or more of the lamps with tungsten ones again to provide a stable load, or to swap out the power supply for a 12V DC LED driver - which is the best option.
Because these units "ride the sinewave" they are dimmable and also have near unity power factor as the current is spread across the full sinewave.
It's best to avoid using these electronic transformers on the same circuits as traditional magnetic ones, as the switch-off voltage spike from the transformers may damage them. It's also best to avoid placing them where they will be covered with thermal insulation, as heat is an issue. They have a history of going bang. In the long term, a traditional properly rated core and coil transformer will outlast these electronic supplies by a huge margin.
The start up circuitry in this unit is odd. It looks like it relies on the rising positive voltage to pass a controlled pulse of current through the 10nF capacitor when the diac triggers, and then relies on the low impedance of the start transistors base circuit to avoid accidental triggering with noise.
If you enjoy these videos you can help support the channel with a dollar for coffee, cookies and random gadgets for disassembly at:-
www.bigclive.com/coffee.htm
This also keeps the channel independent of KZbin's advertising algorithms allowing it to be a bit more dangerous and naughty.