zener diode voltage divider

[aesoton]

hello all again,
quick qs

I need to get a 1.5v supply from a 9v battery.
I want to use a zener diode to do this.
attached are two drawings 1st with a 7.5V zener in series, the second with a 1.5v zener in parallel. Am I right in thinking that you cannot get a 1.5V zener diode. Therefore does the 7.5V zener in series do the same job of creating a 1.5V supply?

 

[richs]

Hiya-

This is "out of the box" and might not field your specific requirements for your design. Small LEDs usually have a forward voltage drop around 1.7V.

If the OP has an LED somewhere in the device and if the voltage "regulation" is rough, then this just might be something to check into.

Of course, there might be significant variances on the forward voltage drop due to process changes.

The series resistance of the LEDs (the internal resistance) might be low enough to provide enough regulation for the desired purpose.

Hope this helps!

Cheers,

Rich S.

 

[zzzjim]

I have used a pair of 1N4002 before now , LEDs can be noisy .
Using a Zener 7v5 drop is risky (even if the 9v was stabilized ) as Zeners fail S/C .

Vary the series resistor for the best stability vs Battery life ( as the 1N4002s can cope with 200mA easily )

A cheap DMM (Not an AVO8 ) is essential to monitor 1.4 - 1.5V

 

[Azhrarn]

Why does people keep saying that Zener diode are not available below 2.4V?

If you go at Digikey, you can find Zener diode as low as 1.8V.

 

[ScottyUK]

Yes, but they are not true 'zeners' and they have a horrible soft kneepoint which makes them a poor choice for regulation.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[Skogsgurra]

Right. They are series connected Si diodes. Terrible.

A forward LED has a much better characteristic. Select IR for around 1.3 V a red for 1.6 a green for around 1.8 V.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...