Hi guys, i have a project to be done but i should find a way to generate negative voltage from positive voltage. The tricky part is that I'm only allowed to use resistors, capacitors, inductors, diodes and op-amps. I have an idea to use zener diodes but actually I don't know how to use. Thanks in advance.
Use a rail-to-rail op amp configured as an astable multi-vibrator connected the plus supply and ground. Couple the square-wave output op amp through a capacitor into two diodes. One diode is connected anode to capacitor and cathode to ground, the other diode connected cathode to capacitor and anode to output. Add a capacitor from the output to ground to filter the resulting negative DC voltage.
The output current of this circuit is limited to about 1/2 of the maximum op amp output current.