Question USB PD to external device ?

[Avi122345]

I'm looking for a solution of powering an external USB device, which consumes about 20W directly from a laptop.
In general, USB 3.2 port can source to external devices up to 15W (even PD). USB PD is a sink up to 100W (for charging the laptop itself).
Someone has any idea how can I operate 20W device directly from the laptop's USB 3 port? TNX

 

[CountMike]

I'm looking for a solution of powering an external USB device, which consumes about 20W directly from a laptop.
In general, USB 3.2 port can source to external devices up to 15W (even PD). USB PD is a sink up to 100W(for charge the laptop itself).
Someone has any idea how can I operate 20W device directly from the laptop's USB 3 port? TNX

Such devices usually have 2 USB-A connectors of which one supplies just additional 5V.

 

[Avi122345]

Such devices usually have 2 USB-A connectors of which one supplies just additional 5V.

TNX. so, how much current can I draw with two USB-A connections?

 

[CountMike]

TNX. so, how much current can I draw with two USBA connections?

Double of one, Cables 2 to one are very simple. plus and minus are connected in parallel thru diodes in current direction so they don't interfere with each other,

 

[Misgar]

Are you trying to use USB-A or USB-C ports on your laptop to power the external "20W" device?

Wikipedia lists the typical power capabilities of different USB ports here:
https://en.wikipedia.org/wiki/USB#Power

If you intend to use USB-A laptop ports:-
High-power SuperSpeed (USB 3.0) device can supply up to 900mA @ 5V = 4.5W
Multi-lane SuperSpeed (USB 3.2 Gen x2) device can supply up to 1.5A @ 5V = 7.5W

Your laptop may not adhere to these specifications, but even if you do manage to "parallel up" two USB-A ports, you might only get 2 x 7.5 = 15W, not 20W.

If your device requires 20W to operate (as opposed to just charging up a battery inside the device) then two USB-A ports won't be enough.

If all you want to do is charge a battery inside the "20W" device, it will simply take longer to charge if you supply it from one or two USB-A ports.

USB-C (multilane) can provide either 1.5A (7.5W) or 3.0A (15W) according to Wikipedia, so that may not be sufficient if the device really needs 20W to operate.

PD (Power Delivery) can provide up to 5A @ 20V = 100W or up to 240W @ 48V with the latest PD 3.1 standard. This would be the best option if your device supports PD, but I doubt your laptop is capable of working as a source of power for PD items.

Pulling 15 to 20W out of a laptop with no charger attached will deplete the battery quite rapidly, unless you have a mains charger connected at the same time.

A typical laptop battery holds 55,000mWh of charge, i.e. 55Wh.

If your "20W" device contains a battery, what is its milliWattHour rating?

Does your "20W" device require 5V only, or a can it operate at PD rates from 5, 9, 15, 20V or even higher voltages up to 48V DC?

 

[Avi122345]

Are you trying to use USB-A or USB-C ports on your laptop to power the external "20W" device?

Wikipedia lists the typical power capabilities of different USB ports here:
https://en.wikipedia.org/wiki/USB#Power

If you intend to use USB-A laptop ports:-
High-power SuperSpeed (USB 3.0) device can supply up to 900mA @ 5V = 4.5W
Multi-lane SuperSpeed (USB 3.2 Gen x2) device can supply up to 1.5A @ 5V = 7.5W

Your laptop may not adhere to these specifications, but even if you do manage to "parallel up" two USB-A ports, you might only get 2 x 7.5 = 15W, not 20W.

If your device requires 20W to operate (as opposed to just charging up a battery inside the device) then two USB-A ports won't be enough.

If all you want to do is charge a battery inside the "20W" device, it will simply take longer to charge if you supply it from one or two USB-A ports.

USB-C (multilane) can provide either 1.5A (7.5W) or 3.0A (15W) according to Wikipedia, so that may not be sufficient if the device really needs 20W to operate.

PD (Power Delivery) can provide up to 5A @ 20V = 100W or up to 240W @ 48V with the latest PD 3.1 standard. This would be the best option if your device supports PD, but I doubt your laptop is capable of working as a source of power for PD items.

Pulling 15 to 20W out of a laptop with no charger attached will deplete the battery quite rapidly, unless you have a mains charger connected at the same time.

A typical laptop battery holds 55,000mWh of charge, i.e. 55Wh.

If your "20W" device contains a battery, what is its milliWattHour rating?

Does your "20W" device require 5V only, or a can it operate at PD rates from 5, 9, 15, 20V or even higher voltages up to 48V DC?

Thank you very much. I can design my device to be PD, however, as you wrote, I cant find a laptop which has a PD source (5 to 25V / 20W)... my device currently works on 15Vdc (it's a kind of a medical device).

Re. the battery inside my device. currently there is no battery. assume it's an option to put a battery, how can it be a solution? I will have to charge it after each usage, no?

 

[Misgar]

If you're designing the unit yourself, why not build it with a separate DC input from a power supply of your choice. Much better than draining the life out of your laptop's battery and probably safer too.

Is this a portable application? If so, it makes the provision of 15V DC for the medical device slightly more complicated but not insurmountable.

You could use an LM2577-15 boost converter IC to convert 5V DC from a portable USB power bank up to 15V for your medical device. When you've finished using the device, just charge the battery bank from a standard 5V 2A USB mains charger.

No doubt there are prebuilt hobbyist 5V to 15V DC converter modules available incorporating this IC or similar. Just make sure the module output is at least 1.5A at 15V (22.5W) and you should be OK. If you integrate the converter into your medical device but keep the 5V USB power bank separate, it should make things easier.

Any more questions just ask.

 

[Avi122345]

Hi,
there is an external P/S currently, but I prefer to remove it and use only USB to laptop connection (commercial preference).
the Laptop battery capacity is non-issue. assume that the laptop is constantly connected to mains.

the device consumes 1.2A @ 15Vdc.
If I boost the 5V to 15V, still I need at least 1.3A (+the converter dissipation) ..... you think USB3.2 can handle this?

 

[Misgar]

The various USB standards define the maximum current a device can draw under a number of conditions. Computer manufacturers implement these standards as they think fit.

USB-C allows the use of a number of different voltages and maximum currents, with PD-capable designs offering much higher powers, typically for charging laptop batteries and similar equipment.

When it comes to drawing power from a USB port on a laptop, you are in the hands of the laptop designer and their company's product brief. Unless there is a specific market for laptops capable of supplying high power to external devices, the designers will conform to the standards. Bigger power transistors cost more money and every cent counts.

The power level you need is above 3.0A @ 5V for USB 3.2 Gen x2 on a Type A connector. At 20W you need to look at USB-C and the associated Power Delivery standards. If you connect your device to a laptop, I would expect it to struggle and then go into foldback current limiting.
https://www.codrey.com/learn/foldback-current-limiting-little-secrets/

You shouldn't have too much trouble finding a USB-C mains power supply that can be adapted for use with your medical device, but I don't think you'll find a "standard" laptop with a USB-C port that will output 20W. There may be specialist industrial (rugged) laptops with unusual facilities costing many thousands of dollars, but I am not aware of any.
https://www.asme.org/topics-resources/content/explore-the-basics-of-usb-c-and-usb-power-delivery

To confirm my suspicions, I suggest you get in touch direct with the manufacturers of any laptops in your price range and ask them if their USB ports can supply 20W output. I doubt you'll have any luck asking the suppliers who sell laptops. They're just the middlemen. You need to contact the designers themselves and that could be exceedingly difficult if you're not in the trade.

From my initial investigation, I think you should switch from powering your 20W device direct from a laptop, over to a standard mains power supply. You could use a USB-C PD GaN brick, but even simpler would be a standard 15V 3A mains power brick. Nowhere near as elegant, but at only $10.99, much cheaper and less demanding on the laptop design.
https://www.amazon.com/100V-240V-Ad...sprefix=15v+dc+3a+power+supply,aps,151&sr=8-5

 

[Avi122345]

Again, connecting an external P/S (USB or just a plug) is always an option.
We prefer to get the power only from a laptop's USB3 port . my question, how can I do so

TNX for your great support.

 

[Misgar]

Answer, you can't. 20W is too much.