Low Zener Voltage?

A better answer depends on several things. What is the frequency of the square wave? How fast must the rise and fall times be?

What is the source of the 5 volt wave? How much load can it tolerate before sagging too much?

What load will be places on the 3.3 volt output?

Some possibilities:

Resistor and green LED divider.

Resistor and 3.3 volt shunt regulator.

Bad Zener?, not enough Resistance and there for you're loading the output source down to much? or maybe you have a capacitance problem?

You should first verify that the zener is operating correctly. connect it to a supply via a resistor that places the zener in it's normal operating range of current. Then perform a Voltage test across it.

"eromlignod"

Eg:

The 1N746A is a 400mW, *nominal* 3.3 volt zener, with rated test current of

The 1N4728 is a 1 watt, *nominal* 3.3 volt zener with rated tests current of 76mA !!!!!

At low current of say 1 mA , the conduction voltage of either type may well be only 2.0 volts.

Low voltage zeners are *darn soggy * and vague voltage references.

Change the zener to one with a higher * nominal* rated zener voltage, till you get the 3.3 volts you want.

....... Phil

Zeners are very 'sloppy' at regulating voltages. You're putting too little current through the zener.

An 'active clamp' is perhaps the best answer (or a dedicated buffer for voltage translation) but do you need to implement this with very few parts ?

Graham

Trust you not to have a clue.

Graham