ZENER DIODES
What are they? Why should I care? How are these used in guitar pedals?
All excellent questions! Let's dive in to see what all the fuss is about. No graphs or complex math here. Read on to learn more!
I took the time to figure out (with a little Google help) about these and how I can apply it to a project I'm currently working on. If you want to read more about my project then
check this out! It's going to be an ultra-breadboarding experience that I may tweak later on down the road.
Here is the schematic symbol for a zener diode.
For this post and purposes of my project/experiment I pulled out a bag of 9.1V zener diodes (1N4739). Putting them through my TC-1 tester shows there's nothing special about them at all with a simple voltage drop of 0.7V. The tester confirms the little black ring is the cathode.
That's weird. I bought these for the 9.1V purpose. Hang on! We need to talk about "zener" breakdown voltage. What is this? Well, if you run some small current from anode to cathode you will see the result above and the diode "steals" about .7 volts before current passes through. What happens when you run current in the opposite direction? Here's where the magic begins....
Whenever you want to test a diode,
ALWAYS make sure you have a current limiting resistor (CLR) of some kind. For me, I used a 470 ohm resistor.
We can arrange the CLR and diode to test where this voltage drop occurs. Like this. Your DMM should be where V Out is.
As the voltage/current passes through it hits the diode and doesn't allow anything to pass
UNTIL it reaches the 9.1V threshold. Anything above that voltage gets passed through the diode.
As an experiment, I threw a passive buzzer at the end of this circuit to act as an overvoltage alarm. The buzzer needs about a Volt in order to kick on.
Pretty neat, huh?
Ok. Let's flip the diode and resistor around to look like this:
This configuration will then act as a
faux voltage regulator. A great way to protect your circuits from accidentally putting too much juice into it. Again, use your DMM at the V Out point. You can see I'm giving it 10V, but only about 9V are coming through. That's because once the diode reaches it breakdown voltage anything over that gets thrown to ground.
Pretty cool, huh?
Ok. Now the question you've really been asking. "How does this apply to guitar pedals?" Let's take a look at a SHO (Super Hard On) schematic. This is the PedalPCB CrackleJack, or at least a portion of it.
See anything familiar yet? That 1N4739 is a 9.1V zener diode that acts as a voltage regulator! As the current passes through from above my little snippet through R2 and into the gate of Q1 it has to touch the zener diode. Anything over 9.1V applied to Q1 will automatically get dumped to ground and saves your BS170 from getting fried by accidental static discharge.
The same concept is true for all zener diodes.
A word of caution. Make sure you're orienting the diode the correct way in order for these little circuit legos to work. Otherwise you may accidentally fry one like I did testing this out.
The more you know.....
BuddytheReow