Voltage source with adjustable negative and positive output

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View


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!


Re: Voltage source with adjustable negative and positive output


Quoted text here. Click to load it

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

Re: Voltage source with adjustable negative and positive output


Quoted text here. Click to load it
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.

Re: Voltage source with adjustable negative and positive output


Quoted text here. Click to load it

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 =^.^=



Site Timeline