# General Electronic Questions

Discussion in 'General Electronics Chat' started by Keith W. Boyd, Jan 18, 2015.

1. ### Keith W. Boyd Thread Starter New Member

Jan 18, 2015
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0
Hello, first time user here. I have a couple of questions I am just unable to find the answers to. I am sure there are smarter people than me on here that may be able to help me out. Thank you in advance if you can.

1. About what is the operating frequency of a normally loaded switching power supply?

2. In a TTL circuit, what is represented by 1.5V?

Which instrument must always be used with the power off in a circuit under test, a voltmeter, ohmmeter, ammeter or frequency counter.

Again, thank you if you can help

2. ### MikeML AAC Fanatic!

Oct 2, 2009
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1. 100kHz to a couple of MHz.
2. A voltage low enough to be a logic zero
3. Ohmmeter, because it injects its own current into the circuit under test so that it can measure the resulting voltage, and thereby compute the resistance.

GopherT likes this.
3. ### GopherT AAC Fanatic!

Nov 23, 2012
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A perfect 3/3 even though the OP didn't bother numbering his third question.

4. ### BillB3857 Senior Member

Feb 28, 2009
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Fantastic answers for a set of homework questions!

5. ### JohnInTX Moderator

Jun 26, 2012
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Hmmm.... I give it 2/3

2) 1.5V is in the TTL gray zone. Logic 0 <= .8V, Logic 1 >=2.0V. 1.5V on a TTL input is usually interpreted as a Logic '1'.

IIRC 1.5V is roughly what voltage an unconnected input measures at.

Last edited: Jan 18, 2015
6. ### GopherT AAC Fanatic!

Nov 23, 2012
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Some days, a kid need a day off.

7. ### JohnInTX Moderator

Jun 26, 2012
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Agreed! The sad thing is that I can't remember what I had for lunch but I remember TTL specs from 40yrs ago.