WIP

USB Adapter Based Power

Most USB adapters are meant for charging devices and providing supplemental power to a battery-powered device. They are not designed to be the sole source of power. When a battery is charging, it is a relatively steady load. A sharp change in load is often referred to as a transient load. The chips commonly used for USB Adapter have a poor transient response since that was not a design goal. However, they are plentiful and inexpensive which makes them very attractive for use in cost-sensitive projects.

The ESP8266 during the boot process presents a big transient load. It goes from 80mA to 430mA. (Appears to be at transmit.) This can be an extreme challenge for an economy switch-mode power supply. (I suspect it's a challenge for most, if not all, SMPS.) The solution I see used for the ESP8266 is a good (most of the time) LDO Power Supply chip. Coupled with low ESR low ESL Ceramic or Tantalum capacitors on the output side. I have seen one ESP8266 development board that uses a low ESR low ESL 100uF Tantalum capacitor to help handle this surge.

All the line-powered IoT devices I have taken apart use an economy SMPS paired with the LDO Regulator approach. A downside to this is the 5.0V rail will sag at times. (Assume WiFi transmit)

This can be a problem if the design has 5.0V ICs that might be sensitive to power fluctuation. An example would be a power monitoring chip that has an analog element that needs clean power. In this case, a split 5.0V supply needs to be created. Depending on the severity of the sag, even other 5.0V digital parts may suffer if they share the ESP8266 LDO's 5.0V rail.

• How does a USB charger work? - A tear-down article on what is inside a USB Adapter.

Considerations when using PC USB Ports for power

Ref: Powering electronics from the USB port

• Of concern is the inrush current due to large capacitors on the +5 volt side. Suggested MAX input side capacitor of 10uf from Page 1, Table 1 of the reference.

USB Cable and Connector Losses

TBA