Hello,
I'm in the process of building several PNP germanium based fuzz pedals. I want to include a voltage inverter circuit so the pedals can use standard pedal power. After scouring the internet I settled on the following circuit from an Aion Proteus. Seems robust with power protection and filtering.
https://postimg.cc/k2JFByv2
I bread boarded the circuit and get the proper inverted voltage at -VA. Then I swapped the power leads around to test the voltage protection and it did not work as I expected; feeding 3v into the ground rail and seeing about -2v at -VA. After noodling on this for a couple days I'm still stuck based on my current knowledge so reaching out see if someone can help me understand what is going on. Here are my questions:
1. What is the difference between GND and PWR_GND in the schematic. On the bread board I'm treating these the same and connecting them to the ground rail witch is connected to the negative side of my power source.
2. There are no resistors in this circuit. Are the capacitors actually doing any filtering?
3. It seems like the power protection is not working if I'm seeing voltage at -VA when I switch the power leads around. Am I thinking about this correctly?
https://postimg.cc/gallery/5tg8HZ6
Hi & welcome..
Unfortunately, no schematic or link posted..
Not sure why the images are not showing in the post.
Schematic - https://postimg.cc/k2JFByv2
Pics of Bread Board - https://postimg.cc/gallery/5tg8HZ6
Welcome airmoss. You need IMG tags around URLs that point to actual images: it's the picture icon on the posting toolbar. Here they are:
(https://i.postimg.cc/fRXHq23f/Screenshot-2024-03-23-at-10-22-26-AM.png)
(https://i.postimg.cc/pXjZLZwS/IMG-8124.jpg) (https://i.postimg.cc/dVK9kCvV/IMG-8125.jpg)
also welcome.
connect ground and ground and don't think about it. if you connect WRONG polarity at the D1 Anode and ground, the diode won't conduct. no volts will appear anywhere else in the circuit. as for if the IC1 supply is reversed, that's outside the bounds of operation for the part - you won't see any performance specs in the datasheet for reversed supply, so the result is unmapped.
Quote from: airmoss63 on March 23, 2024, 02:24:30 PM1. What is the difference between GND and PWR_GND in the schematic. On the bread board I'm treating these the same and connecting them to the ground rail witch is connected to the negative side of my power source.
2. There are no resistors in this circuit. Are the capacitors actually doing any filtering?
3. It seems like the power protection is not working if I'm seeing voltage at -VA when I switch the power leads around. Am I thinking about this correctly?
For the simple setup, there is no difference as D.A. says. There may be a difference in noise performance, as some ways of wiring the grounds can let through a whine caused by the switching currents.
There is no need for resistors, as the capacitors are not "filtering" in the sense you mean. The circuit works by filling up the input-side 10uF capacitor with charge, then dumping that charge into the 47uF output cap. It's a slightly different way to use the capacitors.
If you have the D1 diode wired properly, the protection will be working, excepting only for any leakage through the Schottky diode. It is possible that the CMOS IC is actually working a little even with the leakage current/voltage and making a voltage on the output. Try putting a 10K resistor across the C9/C10 output caps and see if it still happens.