1N5226B for power - Electronic Circuits Projects Diagrams Free

AtomSoft · 5th November 2009, 12:17 AM

would it be possible to use this diode to turn 5v to 3.3v for a display ? using less than 500ma

Papabravo · 5th November 2009, 03:13 AM

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?

atferrari · 6th November 2009, 12:17 AM

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 · 6th November 2009, 03:07 AM

Quote:

Originally Posted by atferrari

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.

kchriste · 6th November 2009, 05:26 AM

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 · 6th November 2009, 09:41 AM

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 · 6th November 2009, 02:44 PM

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.

AtomSoft · 6th November 2009, 03:27 PM

wow lots of replies heh no time to read right now but can some people comment on this 1 qurstion:

what are 3.3v zenors usefull for?

Papabravo · 6th November 2009, 04:17 PM

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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5th November 2009, 12:17 AM	#1
AtomSoft	1N5226B for power would it be possible to use this diode to turn 5v to 3.3v for a display ? using less than 500ma __________________ AtomSofts eBay Store AtomSoftTech: C18 TIPS & TRICKS v9 PDF Nokia 6100 Driver/Software My Name: Jason Lopez http://atomsofttech.info/ \| My YouTube Videos! My Favorite Store: dipmicro Electronics

5th November 2009, 03:13 AM	#2
Papabravo	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? __________________ We never have time to do it right; but we always have time to do it over. Last edited by Papabravo; 5th November 2009 at 03:22 AM.

6th November 2009, 12:17 AM	#3
atferrari	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. __________________ Agustín Tomás In theory, there is no difference between theory and practice. In practice, however, there is.

6th November 2009, 05:26 AM	#5
kchriste	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. __________________ Inside every little problem, is a big problem trying to get out.

6th November 2009, 09:41 AM	#6
Mr RB	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.

6th November 2009, 02:44 PM	#7
Papabravo	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. __________________ We never have time to do it right; but we always have time to do it over.

6th November 2009, 03:27 PM	#8
AtomSoft	wow lots of replies heh no time to read right now but can some people comment on this 1 qurstion: what are 3.3v zenors usefull for? __________________ AtomSofts eBay Store AtomSoftTech: C18 TIPS & TRICKS v9 PDF Nokia 6100 Driver/Software My Name: Jason Lopez http://atomsofttech.info/ \| My YouTube Videos! My Favorite Store: dipmicro Electronics

6th November 2009, 04:17 PM	#9
Papabravo	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. __________________ We never have time to do it right; but we always have time to do it over.