Voltage source with adjustable negative and positive output

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!

Reply to
MRW
Loading thread data ...

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

Reply to
vic

The function of the Fadj pin is explained on page 11 of the data sheet:

formatting link

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.

Reply to
John Popelish

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 =^.^=

Reply to
colin

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.