Voltage source with adjustable negative and positive output

[MRW]

Hello .... I have an old MAX038 IC. I wanted to build a simple signal
generator. One of the pins in the IC datasheet accepts +/- voltages to
adjust the frequency at the output. I was wondering if anyone can give
me some tips on how I can build a voltage source that has one
adjustable output that can range from -2.5V to +2.5V.

I was originally thinking of using two voltage regulators with
adjustable positive and negative outputs. I could then switch between
the two if I wanted to adjust my frequency up or down from the nominal
value, but I figured it'd be more interesting to build just one circuit
that has one output that goes from negative to positive.

I appreciate schematics, but what I really want is a resource that
explains to me how each part of it works and the concepts behind it.
I'm still learning. Thanks!

 

[vic]

Hello .... I have an old MAX038 IC. I wanted to build a simple signal
generator. One of the pins in the IC datasheet accepts +/- voltages to
adjust the frequency at the output. I was wondering if anyone can give
me some tips on how I can build a voltage source that has one
adjustable output that can range from -2.5V to +2.5V.

I was originally thinking of using two voltage regulators with
adjustable positive and negative outputs. I could then switch between
the two if I wanted to adjust my frequency up or down from the nominal
value, but I figured it'd be more interesting to build just one circuit
that has one output that goes from negative to positive.

I appreciate schematics, but what I really want is a resource that
explains to me how each part of it works and the concepts behind it.
I'm still learning. Thanks!

The MAX038 already requires a symmetric +/- 5V power supply, just use a
voltage divider across this power supply to get any voltage between -5
and +5V. You can use a potentiometer and 2 resistors to limit the range
to -2.5V - +2.5V.

Something like this :
,--- slider, [-2.5V, +2.5V]
v
-5V o---[ R ]---[ 2R potentiometer ]---[ R ]---o +5V

vic

 

[John Popelish]

Hello .... I have an old MAX038 IC. I wanted to build a simple signal
generator. One of the pins in the IC datasheet accepts +/- voltages to
adjust the frequency at the output. I was wondering if anyone can give
me some tips on how I can build a voltage source that has one
adjustable output that can range from -2.5V to +2.5V.

I was originally thinking of using two voltage regulators with
adjustable positive and negative outputs. I could then switch between
the two if I wanted to adjust my frequency up or down from the nominal
value, but I figured it'd be more interesting to build just one circuit
that has one output that goes from negative to positive.

I appreciate schematics, but what I really want is a resource that
explains to me how each part of it works and the concepts behind it.
I'm still learning. Thanks!

The function of the Fadj pin is explained on page 11 of the
data sheet:
http://pdfserv.maxim-ic.com/en/ds/MAX038.pdf

The input is a voltage signal (functioning over a +2.4 to
-2.4 volt range), but the pin also has a -250 uA current
load applied internally, so that a variable resistor to the
+2.5 volt reference can produce a variable voltage based on
the current passing through it. a 20k variable resistor
would drop between zero and 5 volts in that situation,
producing +2.5 to -2.5 volts for the input.

This approach is shown on page 9.l.

 

[neon]

I asume you have +/- supplies the input current requirement is very small a pot can do it very nicely without the regulators and the bells and whistles. you are going to very it anyhow just for safety provide a diode clamp to a divider of +/- 2.5 . there are regulators that you may use in TO18 can but it is up to you.

 

[colin]

Hello .... I have an old MAX038 IC. I wanted to build a simple signal
generator. One of the pins in the IC datasheet accepts +/- voltages to
adjust the frequency at the output. I was wondering if anyone can give
me some tips on how I can build a voltage source that has one
adjustable output that can range from -2.5V to +2.5V.

I was originally thinking of using two voltage regulators with
adjustable positive and negative outputs. I could then switch between
the two if I wanted to adjust my frequency up or down from the nominal
value, but I figured it'd be more interesting to build just one circuit
that has one output that goes from negative to positive.

I appreciate schematics, but what I really want is a resource that
explains to me how each part of it works and the concepts behind it.
I'm still learning. Thanks!

the data sheet gives a clue if I assume what you are trying todo correctly,
a 5vttl pll circuit the output of wich goes to a resistive divider down
to -5v,
or you could use a 2.5v bandgap device pulled down to -5v that would turn 0
to 5v into 2.5 to -2.5v

Colin =^.^=