General Electronic Questions

Keith W. Boyd

Joined Jan 18, 2015
1
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

MikeML

Joined Oct 2, 2009
5,444
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

Joined Nov 23, 2012
8,012
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.
A perfect 3/3 even though the OP didn't bother numbering his third question.

BillB3857

Joined Feb 28, 2009
2,562
Fantastic answers for a set of homework questions!

JohnInTX

Joined Jun 26, 2012
4,669
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.

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GopherT

Joined Nov 23, 2012
8,012
Fantastic answers for a set of homework questions!
Some days, a kid need a day off.

JohnInTX

Joined Jun 26, 2012
4,669
Some days, a kid need a day off.
Agreed! The sad thing is that I can't remember what I had for lunch but I remember TTL specs from 40yrs ago.