pi power supply

[glenn jarrett]

looking to power my pi4 from the original power supply as i have measured how much current my pi draws from boot up to running with usb pen drive draws 1.2 A max once settled after boot about 1.1A.
i know its pointless giving the pi a clean supply
but could i use the pi supply to give my tone board a clean supply by using TPS7A4700 regulator i know the regulator will need 7v or so volts to drop back down to 5v so could i use a step up buck set at 5v in 7v out then through the reg board to the tone board ?
or would this be a waste of time
http://rover.ebay.com/rover/1/710-5...0001&campid=5338728743&icep_item=174288170852
http://rover.ebay.com/rover/1/710-5...0001&campid=5338728743&icep_item=401742996970

20200522_153338 by glenn jarrett, on Flickr
CamScanner 05-22-2020 22.06.23_1 by glenn jarrett, on Flickr

 

[sq225917]

It measured pretty damn well in the ASR write up on a boggo supply. If it was mine I'd be tempted to feed each stage directly and cut the usb 5v if possible. If not possible to split them all I'd likely leave it alone.

 

[glenn jarrett]

According to this i found on the Khadas forum the power is cut off on usb when externally powered

Note that when an external power source is connected via pins 1 and 21, USB power input is automatically cut-off; however the USB-data-signal is still permitted

 

[S_J]

How will you get rid of the noise generated by the boost (not buck btw) convertor? You probably already know the ideal answer is a separate fully linear supply...

 

[MJS]

I cobbled together a linear supply out of surplus Naim supercap boards. By using a TPR configuration and green LEDS on the regulators you can get exactly 5.2V out which suits the pi perfectly.