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SiriusHardware · 19th Feb 2021, 5:09 pm

Regarding the current available from the +5V pin on the GPIO connector, the answer to this seems to vary, probably because it really has changed as the Pi has developed.

One school of thought says that the +5V out is on the protected side of a 1A fuse which is also used by everything else on the board which can use +5V including the USB ports and the PI itself, which runs on the 5V regulated down to 3V3. What you have is therefore whatever portion of the available 1A the Pi is not using itself.

Where this is the case then obviously my earlier suggestion of taking power from one of the USB ports instead will make no difference.

Other sources have the +5V out on the GPIO pins directly connected to the USB +5V-in which powers the Pi. I think the likely answer is that later models of the Pi probably became more capable in this respect as end users started to demand the right to dangle USB powered HDDs, etc, off them.

19th Feb 2021, 5:09 pm	#6
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,556	Re: Reading PROMs with a Raspberry Pi Regarding the current available from the +5V pin on the GPIO connector, the answer to this seems to vary, probably because it really has changed as the Pi has developed. One school of thought says that the +5V out is on the protected side of a 1A fuse which is also used by everything else on the board which can use +5V including the USB ports and the PI itself, which runs on the 5V regulated down to 3V3. What you have is therefore whatever portion of the available 1A the Pi is not using itself. Where this is the case then obviously my earlier suggestion of taking power from one of the USB ports instead will make no difference. Other sources have the +5V out on the GPIO pins directly connected to the USB +5V-in which powers the Pi. I think the likely answer is that later models of the Pi probably became more capable in this respect as end users started to demand the right to dangle USB powered HDDs, etc, off them.