Glass Tiles: USB Charger Current Waveforms

Looking at what comes out of various USB chargers, with the Tek current probe monitoring the juice:

USB Current-Probe Extender - in action
USB Current-Probe Extender – in action

First, a known-good bench supply set to 5.0 V:

Tiles 2x2 - bench supply - 50 mA-div
Tiles 2×2 – bench supply – 50 mA-div

The yellow trace is the Glass Tile Heartbeat output, which goes high during the active part of the loop. The purple trace shows the serial data going to the SK6812 RGBW LEDs. The green trace is the USB current at 50 mA/div, with the Glass Tile LED array + Arduino drawing somewhere between 50 and 100 mA; most of that goes to the LEDs.

The current steps downward by about 10 mA just after the data stream ends, because that’s where the LEDs latch their new PWM values. The code is changing a single LED from one color to another, so the current will increase or decrease by the difference of the two currents.

A charger from my Google Pixel 3a phone (actually made by Flextronics and, uniquely, UL listed), with Google’s ever-so-trendy and completely unreadable medium gray lettering on a light gray plastic body:

Google Pixel charger - dataplate
Google Pixel charger – dataplate

The current waveform looks only slightly choppy:

Tiles 2x2 - Google Flextronics charger - 50 mA-div
Tiles 2×2 – Google Flextronics charger – 50 mA-div

An AmazonBasics six-port USB charger from tested by Intertek:

AmazonBasics charger - dataplate
AmazonBasics charger – dataplate

The waveform:

Tiles 2x2 - Amazon Basics Intertek Basics charger - 50 mA-div
Tiles 2×2 – Amazon Basics Intertek Basics charger – 50 mA-div

A blackweb (their lack of capitalization) charger, also made tested by Intertek:

blackweb charger - dataplate
blackweb charger – dataplate

The current:

Tiles 2x2 - blackweb charger - 50 mA-div
Tiles 2×2 – blackweb charger – 50 mA-div

Finally, one from a lot of dirt-cheap chargers from eBay:

Anonymous white charger - dataplate
Anonymous white charger – dataplate

Which has the most interesting current waveform of all:

Tiles 2x2 - anon white charger - 50 mA-div
Tiles 2×2 – anon white charger – 50 mA-div

A closer look:

Tiles 2x2 - anon white charger - pulse detail - 50 mA-div
Tiles 2×2 – anon white charger – pulse detail – 50 mA-div

From the 75 mA baseline, the charger is ramming 175 mA pulses at 24 kHz into the filter cap on the Arduino Nano PCB! The green trace has a few seconds of (digital) persistence, so you’re seeing a lot of frequency jitter; the pulses most likely come from a voltage comparator controlling the charger’s PWM cycle.

It’s about what one should expect for $1.28 apiece, right?

They’re down to $1.19 today: who knows what the waveform might be?

Update: Having gotten a clue from a comment posted instantly after I fat-fingered the schedule for this post, I now know Intertek is a testing agency, not a manufacturer.

5 thoughts on “Glass Tiles: USB Charger Current Waveforms

      1. Of course, there is no guarantee that the Intertek mark is genuine. A lot of Chinese junk manufacturers will slap a mark on anything, whether it has been tested or not.

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