Op Amp Hookup Help Please

Discussion in 'Electronic Basics' started by stilltrying, Nov 28, 2005.

1. stilltryingGuest

I'm not an experienced electronics person, and so have a "stupid question".
I have a device that provides an "on" signal intermittently at 2.7 volts DC.

When the "on" of 2.7 volts is available, I need to have a "sub-circuit"
receive an "on" of 5.0 volts. I have a source of 5.0 volts on the board.
I've been told I need to use an op amp to do this, so I bought two NTE 928M
op amps. I've tried to get this to perform as I need, but can't. HELP
please!!! I put resistors in somewhere, but where and how big?
tanksalot
S.F.

2. Bob MonsenGuest

An opamp is a super high gain amplifier. So amplify the difference between
your input and a reference. Your NTE928M won't be able to pull the output
up to 5V unless you give it about 7V Vcc. A better way would be to use a
comparator with an open collector output. Google for comparator. Also
google for 'hysteresis'.

---
Regards,
Bob Monsen

The chief aim of all investigations of the external world should be to
discover the rational order and harmony which has been imposed on it by God
and which He revealed to us in the language of mathematics.
- Johannes Kepler

3. ehsjrGuest

Post the circuit you are using. And give us information on
the circuit you are feeding the +5 volts to. How much current
does that circuit draw from the % volt "on" ?

The NTE 928 can't provide 5V output with a supply of only
5 volts. It won't do what you want directly, but first things
first - get it working. Once you get the NTE 928 working, we can
get into the necessary additional circuitry.

Or we can give you a circuit that does not use the NTE 928M,
but that will work properly.

By the way NTE parts cost more, so it's a good idea to look
beyond NTE for your parts in the future.

Ed

4. Bill BowdenGuest

When the "on" of 2.7 volts is available, I need to have a "sub-circuit"
You could do it with a couple transistors and resistors, but it's
difficult to describe.

How much current is availiable from the 2.7 source, and how much
current is required by the 5 volt "sub-circuit" ?

-Bill

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