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Old 22nd Oct 2018, 3:17 pm   #11
SiriusHardware
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Join Date: Aug 2011
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Default Re: Retired Texas TI99/4A engineer needs help please.

Quote:
Originally Posted by cmjones01 View Post
I'd say the +5V rail needs to be able to deliver about 2A to power the computer happily, judging by my experience of other machines of the era. It might be somewhat less, though.
Actually I'm going to revise my guess (0.5A-1A) because if that was the current requirement the 5V regulator would probably have been a three terminal 7xxx series, just as the others are.

Therefore, the maximum output current required from the 5V rail is likely to be in excess of anything that a 7805 could comfortably supply. The standard versions do 1A maximum. There are tougher 'evolved' versions of the 7805 which can handle more output current but, being linear regulators, they would need a very big heatsink to do so.
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