Set it before you plug it in
The board has no memory, but the levers do. A board left on 20 V for a laptop job is still on 20 V, and the output only reveals that a moment after the cable goes in.
The first moment is always 5 V
Plug the cable in and the terminal sits at 5 V. That is not the board being slow; it is how USB-C works. A source has no idea what it is connected to until the sink talks to it, so it starts everything at the one voltage that cannot hurt a phone, and only moves when the negotiation lands.
Which means the output does this, every time: 0 V, then 5 V, then whatever you asked for. If you asked for 5 V, nothing appears to happen. If you asked for 20 V, there is a step, and it arrives with no warning at all.
The dangerous case is a board you used last month
There is nothing on this board that remembers a setting, which sounds reassuring and is the opposite. The levers are the setting. A board that was driving a laptop-voltage load in January is still asking for 20 V in March, and it looks exactly like a board set to 5 V from any angle except directly at the levers.
So the order is:
- Read the levers against the table on the back.
- Set them to what you want, with the corner of a small screwdriver.
- Plug in the charger with nothing on the screw terminal.
- Meter across VCC and GND, and wait two seconds.
- Unplug the charger, connect the load, plug the charger back in.
Steps three and four take ten seconds and they are the difference between finding a mistake and finding it out.
There is no fuse
Worth saying plainly, because the listing's talk of built-in protections invites the opposite assumption. The chip has over-voltage and over-temperature protection for itself, and the charger has its own current limit. Between them is a bare board: no fuse, no polyfuse, no TVS diode, nothing that opens when your circuit draws more than it should.
Whatever a 65 W charger is willing to deliver into a fault, this board will pass straight through to your build. If that matters for what you are making, the protection has to go on your side of the screw terminal — fuses and PPTCs is the place to start.
When it does not work
You measured during the first moment, before the negotiation finished. USB-C starts every connection at 5 V and the chip's request lands afterwards, so an early reading tells you nothing. Wait two seconds with the cable in, then read again.
The chip's datasheet lists dynamic adjustment of the requested voltage among the family's features, so moving a lever will generally make it ask again. Do not rely on it with a load connected: the intermediate states as a lever crosses over are real, and your load sees all of them.
Every board you use, yes, and every time you reuse one. There is nothing on the board that says what it was last set to except the levers themselves, so reading them is the only way, and reading them takes about a second.
The board can only ask. Which voltages your charger actually owns decides what you get, and it will not tell you when it says no.
What the charger must offer →Edit this page — content/books/pd-trigger/set-it-before-you-plug-it-in.mdx
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USB-C PD Trigger, 100 W Decoy 5–20 V, 12-Pack
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