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1N5226B for power

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Papabravo

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Not reliably. A resistor and a zener diode will provide a reference voltage near 3.3V. Depending on the actual zener current you could be plus or minus 10% or more especially with low values of zener voltage. As your load trys to pull more current from the point between the resistor and the zener the resistor will heat up and affect the zener current. It is a really bad idea.

Just use an LDO fer pitys sake. What earthly reason could you have for asking such a question?
 
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atferrari

Well-Known Member
If he still insists, he should use a zener to drive a transistor able to handle the required current.

Anyway, LDO regulator seems the reasonable way to go.
 

Papabravo

Well-Known Member
If he still insists, he should use a zener to drive a transistor able to handle the required current.

Anyway, LDO regulator seems the reasonable way to go.
I would agree, except for the low value of the zener's knee. A zener regulator needs a bit more room to work with than the difference between 5 and 3.3V. It is just too squirrelly in that region.

For example suppose the zener voltage was high by 10%, so 3.3 + .33 = 3.63, and the 5V supply was low by 5%, so 5 - .25 = 4.75. Now 4.75 -3.63 = 1.12 Many pass trasnsistors will eat up this difference in Vce at any appreciable current.
 
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kchriste

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If you want to use simple components, then 2 silicon diodes and one schottky in series with the 5V line will give you apx 3.3V. The proper solution is to use an LDO if possible, though the diodes work OK.
 

Mr RB

Well-Known Member
3 silicon diodes works better. ;)

The nokia displays use very little power, the 3 silicon diodes like 1N4148 will drop about 0.5v at such low currents giving about 3.5v for the display. It might even require a resistor in parallel with the display to increase the current enough to get the voltage down to 3.3v.
 

Papabravo

Well-Known Member
Well silicon diodes in series is different that the OP's question about how to use a zener diode. Of course a zener diode can be used as an ordinary diode, but it would seem odd to do that.

The real point is that the forward voltage of 1 or two diodes plus a Schottky can't be accurately controlled and is load dependant. The use for the Noikia display did not occur in the original post.
 

Papabravo

Well-Known Member
Clipping. A zener to GND on an analog input prevents it from going much above 3.3 V or more than 0.7V below GND -- it is still a diode. It also adds capacitance to the analog input and so must be used with care.

Back to Back Zeners can be used for input protection.

You can put two in seies to make one with a tolerance of 20%

Don't forget that most diodes have a reverse breakdown characteristic. Look for a parameter called PIV. That is not the zener voltage, but it is not too far away from that level. In a zener diode this reverse breakdown characteristic is enhanced and manipulated.
 
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