Furthering the "Prostitution" of USB C PD – A "Travel" Power Supply

[For The Popcorn]

I often find a small portable power supply would be very handy. I had this idea, which furthers Externet 's disgust of the prostitution of USB power supplies, to connect a USB C PD 20 volt trigger to one of the common buck/boost modules that have a display and all the whistles (adjustable voltage, current, power consumption tracking).

As I had a 20 volt USB C PD trigger (negotiates with the power supply to give the desired voltage) with header pins soldered on, it was simple enough to test. The PD trigger is barely larger than a USB C connector and in fact are available built into a USB cable.

I connected the trigger to the module and connected it to my phone charger which was convenient. Instant success, with the output voltage range adjustable from 0.6 – about 20 volts. Awesome!

My phone charger is not USB C PD, but has QC high rate charging, which has the potential to supply 9 volts. I put my USB meter in line, and found only 5 volts being supplied to the module, which was expected as the charger is not USB C PD.

Upwards and onwards. Connected a USB C PD charger to the trigger and module, and the module was happy to provide its full range of 30 volts.
The USB C PD charger I tested with can supply 15 volts maximum, so the trigger and charger negotiated to 12 volts. Beautiful. So this 3" × 2" × 1.5" power supply module can be connected to any handy USB charger to serve my needs. That's pretty cool.

The power supply module shown here is an XY-SK35 but many variations are available in the same package. This one is a little low on the features list.

 

[For The Popcorn]

In case you don't understand why the USB C PD trigger is necessary or at least desirable:

At 5 volts, USB power supplies can supply at most 10 or 15 watts.

At 20 volts, a USB C PD supply can deliver 60 watts.

The buck/boost module is a switching power supply. Unlike linear regulators, where excess voltage is dissipated heat, switching power supplies are 80% or better at converting input wattage to output wattage at any voltage in their range.

15 watts supplied by a non-PD charger could supply about 1 amp at 12 volts through the buck/boost module. 60 watts supplied by a USB C PD charger could supply about about 4 amps at 12 volts through the buck/boost module.

I don't know but I speculate that starting with a higher voltage also results in higher efficiency in the buck/boost module.

 

[Papabravo]

It is surprising that you would imagine starting with a higher voltage would imply higher efficiency. After decades of working with SMPS devices I can tell you that there are many other things that have a greater effect on efficiency than the choice of input voltage.

 

[For The Popcorn]

As I said, it was only a thought. But my rational for supplying the greatest possible voltage – within the limits of the dc/dc converter module – still apply.

 

[AnalogKid]

I don't know but I speculate that starting with a higher voltage also results in higher efficiency in the buck/boost module.

A higher input voltage means a higher voltage across the transformer primary. All other things, including the output power, being equal, this means lower primary current and hence lower power loss in the primary winding.

If the buck/boost supply is a non-isolated circuit, then a higher input voltage translates into a lower average input current. This could lead to slight efficiency gains in several components, but the effect is more subtle.

ak

 

[Papabravo]

This discussion would be more meaningful if we had a schematic instead of speculations about what might or might not be going on under the hood.

 

[For The Popcorn]

There's no need to bog this down in needless irreverent detail as is wont to do here. The point here isn't to discuss the probably slight change in efficiency vs input voltage.

The XY-SK35 buck/boost converter is a commercial module made in China. It appears to be well made and preforms as claimed. I make no apologies that I don't have a schematic to post. I believe one might be available but a reasonable amount of searching didn't discover one.

The point is to demonstrate a simple, small power supply that can be powered by a USB charger in hopes that this neat idea may be useful to others. Also, some explanation is provided to understand USB C PD, and the use and purpose of a trigger nodule.

 

[For The Popcorn]

More info about the XY-SK35 module features and operation may be found here (pdf).

 

[Papabravo]

There's no need to bog this down in needless irreverent detail as is wont to do here. The point here isn't to discuss the probably slight change in efficiency vs input voltage.

The XY-SK35 buck/boost converter is a commercial module made in China. It appears to be well made and preforms as claimed. I make no apologies that I don't have a schematic to post. I believe one might be available but a reasonable amount of searching didn't discover one.

The point is to demonstrate a simple, small power supply that can be powered by a USB charger in hopes that this neat idea may be useful to others. Also, some explanation is provided to understand USB C PD, and the use and purpose of a trigger nodule.

There is also no need to engage in speculation for which you have no evidence. Stick to what you know.

 

[CatMan]

Papa, when you're wrong, you're wrong, just admit it or quit it; we all make mistakes.
For a given boosting module, there are no other things you can change and the higher input voltage will result in higher efficiency; no iffs and buts.

 

[ChrisP58]

Papa, when you're wrong, you're wrong, just admit it or quit it; we all make mistakes.
For a given boosting module, there are no other things you can change and the higher input voltage will result in higher efficiency; no iffs and buts.

CatMan. While your statement is generally true for boost converters, it's not generally true for buck converters, where the best efficiency is usually when the input voltage is just a little above the output voltage.

Since the product that For The Popcorn is discussing in this thread is a Buck/Boost converter, the input voltage for the best converter efficiency may very well depend on it's operating mode at the moment.

One area where higher voltage almost always equates to higher efficiency is in power distribution. Higher voltage means less current in the input wiring, which means lower I2R losses in the same wire, or, the ability to carry the same power with smaller wires. And that point is why USB-C works like it does. Can you imagine the wire and connector size if you had to deliver 60 + Watts at 5 Volts?

​

 

[AnalogKid]

Please post all of the text on the top of each IC.

Can you give us photos so we can see any logos?

ak

 

[For The Popcorn]

Please post all of the text on the top of each IC.

Can you give us photos so we can see any logos?

ak

No. This topic is off into the weeds as per usual here. The module is what it is, and I believe it preforms to its specs.

The only control I have over the input voltage is to plug it into a standard 5 volt USB power supply and limit its operating range or plug it into a USB C PD chargerand get 20 volts if the charger supports it, or some lesser voltage if it does not. I made a passing remark for supposing the buck/boost module might preform better with higher input voltage, and been called a fool for making that comment (with no evidence to support that).

I shared what I consider to be a neat idea that might be useful to others. I'm sorry it doesn't have any problems to fix, it's not a blurry picture of a crattered (or not) part that somebody is sure will fix something, or a question like "Wouldn't you agree that this is a terrible design?" or "My Swordfish Basic Code isn't doing the right thing."

 

[For The Popcorn]

It could be smaller. This is a box I had that suits my fancy. 3-D printed enclosures are available for these modules.

 

[For The Popcorn]

I did some load testing on the XY-SK35 module and did encounter a problem.

The module is rated for 5 – 30 VDC, with the minimum input voltage > 7 recommended for the full range of operation. The voltage of the standard USB charger I happened to use dips below 5 volts with load, causing the module to shut down. I have a heftier module rated at 5.1 volts I'm going to try when I get a chance – hopefully it will be stiff enough to maintain operation.

With a USB C PD charger supplying 12 volts, the module worked well. I'll post the data and results in another thread when I'm finished testing.

One thing to bare in mind with a boost converter – if you double the output voltage as an example, you double the current draw from the input source + the loss from less than 100% efficiency. If you want to draw an amp at 30 volts, you would need 6 amps + from a 5 volt supply.

 

[AnalogKid]

One thing to bare in mind with a boost converter – if you double the output voltage as an example, you double the current draw from the input source + the loss from less than 100% efficiency. If you want to draw an amp at 30 volts, you would need 6 amps + from a 5 volt supply.

Yup.

TNSTAAFL: There's no such thing as a free lunch.

Robert Anson Heinlein


ak

 

[Nigel Goodwin]

Yup.

TNSTAAFL: There's no such thing as a free lunch.

Robert Anson Heinlein


ak

Haven't you missed an 'A' out? - TANSTAAFL - There ain't no such thing as a free lunch.

I'm a big Heinein fan

 

[For The Popcorn]

I'm a Larry Niven fan. TANJ seems really appropriate for current times.

 

[Nigel Goodwin]

I'm a Larry Niven fan. TANJ seems really appropriate for current times.

I like Larry Niven as well, and particularly E.E. 'Doc' Smith.

 

[AnalogKid]

Haven't you missed an 'A' out? - TANSTAAFL - There ain't no such thing as a free lunch.

Yeah. I knew it didn't look right, but I posted it anyway.

The internet is a harsh mistress.

ak