Power consumption?

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Joined: Jan 1 2015
Posts: 47

Can anyone tell me what the actual power draw is on the 5 volt rail?

Just trying to know how much headroom I have for my keyboard.

len

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gsmcten's picture
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Joined: Oct 4 2005
Posts: 2609
Re: Power consumption?

8008guy,

I'm not the person who can help in that department,
although there are many here who can.

(Steven pulls out a megaphone, raises it to his lips and yells...)
Anyone know?

Steven Smile

__________________

Steven (gsmcten)

"Apple ][.....It's ALIVE!!!!!"

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Joined: Jun 5 2008
Posts: 380
Re: Power consumption?

I think you will be limited by the connector rating on the keyboard socket, not by the power supply.

The entire board draws about .25 amps from a 110 volts AC circuit in steady state. Be aware that there is a decent power up surge, I've blown a few .5 amp fast blow fuses during the power up.

.25 amps steady state would convert to about 25 watts. If all the power went to five volts that would be about 5 AMPs, but this is unrealistic, since there are losses in the power supplies and some of the power is consumed by the other supplies. Assume 50% losses in the supplies and 33% of the power went to the other voltage rails - that would give you 5 X .5 * .67 = 1.67 AMPs consumption on the 5 volt rail. I have no idea how close this is, but it's what I'd call an educated guess. Best way to know for sure, would be to measure directly on the output of the 5 volt regulator.

regards,
Mike Willegal

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Joined: Jan 1 2015
Posts: 47
Re: Power consumption?

My keyboard draws 225 ma. For the connector that. Shouldn't be an issue. Just wasn't sure how close the entire board was to the rating of the regulator.

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Joined: Jun 5 2008
Posts: 380
Re: Power consumption?

You should be fine.

The PS/2 spec is 275 milliamps and a lot of PS/2 keyboards are pretty close to the limit. The only trouble I've had with PS/2 keyboards, when using my adapter, was when I built the first one and used an extra long ribbon cable.

regards,
Mike W.

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Joined: Jan 1 2015
Posts: 47
Re: Power consumption?

Thanks Mike, that's good to know.

Len