I'm trying to flash new firmware onto an ESP8266EX chip. The chip requires 3.3v and 80 mA (average).

My USB to TTL programmer (FTDI chipset) can supply 3.3v but only at 50 mA.

Here is what I'm thinking:

[USB-to-TTL] 3.3v -> not connected
[USB-to-TTL] RX   -> [ESP8266] TX
[USB-to-TTL] TX   -> [ESP8266] RX

[Bench PSU] GND   -> [USB-to-TTL] GND and [ESP8266] GND    
[Bench PSU] 3.3v  -> [ESP8266] VCC

Therefore, the USB-to-TTL adapter is powered by USB, the ESP8266 is powered by the bench PSU, and all grounds are connected together. (NOTE: I know it's important to NOT use the earth ground on the PSU but instead use the floating ground/black terminal)

Does that sound correct?

  • 1
    \$\begingroup\$ Note that the extreme limitation you are seeing comes from the on-chip regulator on the FTDI which isn't really meant to source much power to other things. A more normal regulator running off the USB 5v could typically power an ESP8266, at least for development purposes. \$\endgroup\$ Jan 3, 2019 at 15:28
  • \$\begingroup\$ Thanks! I've seen the Sparkfun Beefy FTDI which has a separate voltage regulator that supports up to 500 mA. \$\endgroup\$
    – SofaKng
    Jan 3, 2019 at 17:36

1 Answer 1


Yes, this should work.

Tying the grounds together provides a common reference point for the UART Tx/Rx signals. Nice work! And no, you don't need to power the ESP8266 from the same source as the programmer.


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