A well-known property of wall warts like power bricks and USB chargers is that they always consume some amount of power even when there’s no connected device drawing power from them. This feels rather wasteful when you have a gaggle of USB chargers constantly plugged in, especially on a nation-sized scale. This is where a new USB-C wall charger by Belkin, the BoostCharger Pro, is interesting, as it claims ‘zero standby power’, which sounds pretty boastful and rather suspect. Fortunately, [Denki Otaku] saw fit to put one to the test and even tear one down to inspect the work of Belkin’s engineers.
Naturally, no laws of physics were harmed in the construction of the device, as ‘zero standby power’ translated from marketing speak simply means ‘very low standby power usage’, or about 3 milliwatt with 0.3 mA at the applied 100 VAC.
Fascinatingly, plugging in an e-marker equipped USB-C cable with no device on the other end caused this standby usage to increase to about 30 mW, clearly disabling the ‘zero standby’ feature. With that detail noted, it was time to tear down the charger, revealing its four PCBs.
The boring answer here is that Belkin didn’t do anything special, but rather followed the Renesas application note for a 65W USB-C adapter with Zero Standby Power:
As can be surmised from the effect of a non-e-marked versus e-marked USB-C cable being inserted, the USB-PD controller IC detects the presence or absence of a cable, and signals the flyback section to mostly shut down. This then leaves a trickle of current for the charger’s ICs as they wait for something to happen. In the (unfortunately restricted) datasheet for the Renesas iW9870 flyback controller IC, we can see this feature described, including how plugging in a USB cable disables the feature.
This feature appears to be somewhat related to how USB power banks work, with them shutting down the outputs if idle, though there are some issues with it backfiring. Some power banks have a ‘trickle charge’ mode where even low amounts of current being drawn doesn’t shut off the output. In the case of this Renesas ‘zero standby power’ feature, it seems to rely on USB cable detection as an equivalent to an active power device.
As noted in the video, this seems to cause issues when inserting an e-marked cable, and some users have reported the charger randomly turning off the output while actively charging from it. Here we’d like to pitch an absolutely bonkers suggestion, and pitch putting a physical on/off switch on the charger – as well as on power banks – rather than try to do more smart guessing.
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This articles is written by : Nermeen Nabil Khear Abdelmalak
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