# Tag Info

1 vote

### Series resistor and Zener as overvoltage protection for ADC input

As you have it, the circuit won't protect your ADC input. The voltage across the zener diode cannot exceed 3.3V, that much you've understood. But the voltage across the resistor can rise to any value. ...
• 7,160
Accepted

### Series resistor and Zener as overvoltage protection for ADC input

You are partly right. The resistor however is misplaced, it should go in series before of the zener. Even if your opamp has a maximum of 23mA drive this doesn't mean he's happy to be essentially ...
• 7,225

### How to fix oscillation of an 'over-discharge protection' circuit for a lead acid battery

Connect the cathode of the Z diode to the load side. It cannot turn on again. To restart the circuit, use a button switch between emitter and collector of the transistor. A catch diode across the ...
• 537
1 vote

### Ac voltage regulator to keep output voltage constant about 6v using diodes

The current for a resistive load = 500 to 3k will depend on the output voltage. The load draws current normally fed into the Zener limited by a current limiting resistor and the voltage mean and Vpp ...

### Select zener for minimal thermal drift

I know the answer, but if you are doing this for a school assignment you should be able to prove it and show your work. If not, a perusal of detailed datasheets (many are not very detailed) and ...
• 328k

### Selecting series resistor for a Zener diode

Your analysis is correct. If the zener is biased with a high resistance, it may regulate at a little lower than the nominal voltage. This means the MOSFET doesn't have as much gate drive and its on-...
• 12.5k

### Selecting series resistor for a Zener diode

Well, that sound reasonable. Personally, within those constraints I’d probably pick the 10V zener and 1M or less, but I’d check and see what typically happens at low zener current and very high ...
• 328k

### MOSFET gate-source protection, in selecting a Zener diode, is there any consequence of the forward voltage / current rating?

There are some problems with your assumptions. A Zener is chosen to protect the gate from exceeding its Vgs max or static max Vgss usually +/-20V so a 15V Zener is suggested. Since the static gate ...
Accepted

### MOSFET gate-source protection, in selecting a Zener diode, is there any consequence of the forward voltage / current rating?

Note that for an N-channel Enhancement-Mode MOS (NEMOS), 1.2V Source-Gate is quite low; most NEMOS will not work appreciably at this low of a voltage. So if indeed using it like this, ensure the ...
• 11.8k

### Is there an analytic expression for the avalanche and Zener diode VI curves?

There is a way to do this, but it might be the long way around. If you have the curves (graphs from the manufacturer), there is software that you can use to capture data points (x,y) from the graph ...

### Is there an analytic expression for the avalanche and Zener diode VI curves?

I don't know about exact physics, but it's often fitted by an exponential e.g. SPICE: https://books.google.com/books?id=pYJHAAAAQBAJ&pg=PA77&lpg=PA77&dq=spice+breakdown+equation&source=...
• 1,035
1 vote

### Can I use a normal diode as a Zener/Varistor ? If not, why not? (focus on Varistor use)

In a pinch you can use a reverse biased base-emitter as an 8 volt zener. It will have a rounder knee than a true zener. The phenomenon is well-known. There's a trick question that asks what the not-...
• 381

### Can I use a normal diode as a Zener/Varistor ? If not, why not? (focus on Varistor use)

Another nail in the coffin from here. Even if you do find diodes that have "reasonably" close breakdown voltage to what you want, they may (will) die. There are "avalanche rated" ...
• 3,428
Accepted

### Can I use a normal diode as a Zener/Varistor ? If not, why not? (focus on Varistor use)

Sort of, but not really. As mentioned by others, voltage is undefined -- indeed in practice, rectifiers are highly overrated. I've measured "400V" diodes breaking down at over 1000 (Ir = ...
• 1,035