The charger that only says 5 V
A 65 W USB-C charger has a 20 V rail inside it. It will not hand it over to you, and it is right not to — nothing has asked. This board is the thing that asks.
The charger is not a 5 V thing
Look at the printing on a modern USB-C charger and you will find a list rather than a number:
5V⎓3A 9V⎓3A 12V⎓3A 15V⎓3A 20V⎓3.25AThose are five separate rails the charger can produce, and it can produce any one of them on demand. What it gives you when you plug something in is the first one, always, every time.
That is not meanness. USB-C is a socket you can plug a phone into, and a phone does not survive 20 V. So the rule is that a supply starts at 5 V and only moves when the thing on the other end of the cable asks — by name, in a protocol called Power Delivery, over a wire called CC.
Asking is the whole job
A USB Power Delivery source sends a list of what it can do, the moment something is connected. It is called the source capabilities message, and it is a list of exactly the rails printed on the case. A sink that can read that list picks one and sends a request back. If the source agrees, it changes its output and tells the sink when the new voltage is stable.
That is a real conversation, with timing and acknowledgements, and it is the only way into the other four rails. There is no jumper on the charger, no resistor you can hang on a data pin, nothing to hold down while you plug it in.
This board contains one chip whose entire purpose is to have that conversation on your behalf, and three levers that tell it which rail to ask for. A board that does that is called a trigger or a decoy, because it is pretending to be a laptop for just long enough to get a laptop's voltage.
What that buys you
A 65 W laptop charger costs less than most bench supplies, comes with over- current and over-temperature protection built in by somebody who does that for a living, and is already on your desk. Once you can select its voltage, it is a 5, 9, 12, 15 or 20 V supply for whatever you are building:
- 12 V for LED strip, fans, car-radio parts and most CCTV cameras.
- 9 V for guitar pedals and the odd radio module.
- 20 V for anything laptop-shaped, and the only way to reach 100 W.
What it is not is a bench supply. There is no current knob, no display, no soft-start and — on this board in particular — no fuse. Chapter four is about where that matters.
When it does not work
That is the correct behaviour and nothing is broken. A USB-C supply starts every connection at 5 V and stays there until a sink asks for something else in the Power Delivery protocol. Without a trigger board in the way, nothing asks, so nothing changes.
No. The voltage is not selected by a pin on the charger; it is the outcome of a conversation on the CC line, with messages and timing. That conversation is what the chip on this board does, and there is no resistor you can add to a plain socket that will do it instead.
A USB-A supply has one 5 V rail and no CC line to negotiate on, so an A-to-C cable gets you 5 V and only 5 V. The board will still power up and its LED will light. You need a supply that advertises Power Delivery for anything above 5 V.
Twelve boards, four strips of header, and the arithmetic nobody does until the bag is open.
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USB-C PD Trigger, 100 W Decoy 5–20 V, 12-Pack
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