Hello guys. I have few questions about pedal circuit protection:
- If I want to protect circuit from voltages bigger than 9v is it enough to use one zener 9,1v diode between ground and +9v or do I need some extra components?
- If I use zener diode connected in that manner do I need to connect 1n400x for reverse polarity protection or no? Will zener protect from reverse polarity?
- How can I protect circuit that uses DC current from AC current?
Thanks in advance
High voltage circuit protection, AC protection
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soulsonic
- Old Solderhand
Information
You can use just a zener to protect the circuit, but if it actually gets powered by too high a voltage for more than a second, it will probably burn up the diode and possibly damage some other things from the resulting heat. Better to have a resistor in series that can burn off the excess voltage and keep things from being damaged. You can take the worst case scenario and use that as a guide to determine good values - for example, design it to be able to regulate an 18v input down to 9v without burning anything - use ohms law to calculate how much current is going to be flowing through the resistor and diode to burn off the excess 9v and choose a value for the resistor that will keep everything from burning up.stole59 wrote:Hello guys. I have few questions about pedal circuit protection:
- If I want to protect circuit from voltages bigger than 9v is it enough to use one zener 9,1v diode between ground and +9v or do I need some extra components?
- If I use zener diode connected in that manner do I need to connect 1n400x for reverse polarity protection or no? Will zener protect from reverse polarity?
- How can I protect circuit that uses DC current from AC current?
Thanks in advance
For example, I had a pedal that had a 9v zener with a 20 ohm 1/4w resistor in series with it to protect the charge pump chip in the power supply. Someone plugged 15v into it and left it on for awhile. The resistor got burned pretty badly, and the diode needed replaced too, but the rest of the circuit was totally fine. If I had designed it better with a more appropriate resistor, it wouldn't have burned up, but in any case only 20cents worth of a resistor and diode were damaged and all the rest of the circuit were just fine.
The zener works for polarity protection too, but you have the same problem of it potentially burning up if that's all you use.
If you connect a 1N400x in series with it, that will also protect it from being damaged by AC, because it will rectify it to DC, but unless you include a sufficiently large filter capacitor after it, you will probably get a bad hum if AC is plugged in.
If you did something like: 1N4001->220uF filter->resistor->zener->220uF filter+100nF filter (the 100nF to better kill any noise from the zener) = probably would work pretty well for most situations.
"Analog electronics in music is dead. Analog effects pedal design is a dead art." - Fran