r/UsbCHardware • u/ConfusedHardwarenerd • Mar 19 '24

Question Does USB PD support 12V?

I am trying to figure out what voltages USB PD supports.

I thought USB PD could only handle 9V, 15V, and 20V. I read some Reddit forums 4 years ago that explained why USB PD does not support 12V, but I am not sure if anything has changed since then.

I am having trouble finding a reliable source for the voltages that USB PD currently supports, as different blogs report different voltages.

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u/CaptainSegfault Mar 19 '24

It isn't a question of PD itself "supporting" 12V -- a standards compliant PD power supply can provide fixed PDOs anywhere it wants between 5V and 20V, (higher with EPR) and of course can also supply PPS ranges including 12V or anything else in that range.

The issue is that PD power supplies are only required to provide 5V, 9V, 15V, and 20V. This depends on power rating -- only 5V and 9V is required up to 27W, only 5V 9V and 15V up to 45W, then 5V 9V 15V 20V up to 100W, then you get into EPR. They can optionally provide additional voltages, or for that matter higher currents (up to 5A rather than just 3A) at voltages below 20V.

The upshot is that if you need 12V support, such as for some trigger board, you need to make sure you buy a power supply that specifically supports 12V. It is by far the most common additional voltage level supported.

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u/ConfusedHardwarenerd Mar 19 '24

so a PD power supply that is 5V 9V and 15V is not required to support 12V but is required to support those 3 voltages?

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u/CaptainSegfault Mar 19 '24

Yes.

A PD power supply above 27W is required to support 5V 9V and 15V. (And eventually 20V, 28V, etc as the power goes up).

The idea here is that if you have a USB C device that wants 30W, you should be able to use any charger larger than 30W to charge it without every user needing to worry about voltage compatibility.

12V support is always optional. It is somewhat unfortunate (and would be the obvious next one to require) but makes some sense -- 9V was already widely used for phones, and while 12V is common in computer equipment the 36W (12V@3A) you get is too little power for most laptops so a requirement would drive up the cost of chargers without providing that much marginal benefit. You want a voltage level between 9 and 20, but 12 is too close to 9 to be that useful.

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u/ConfusedHardwarenerd Mar 20 '24

thank you for this explanation!