zener diode voltage divider
zener diode voltage divider
(OP)
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?
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?





RE: zener diode voltage divider
The second approach needs a series resistor. It will provide a very stable voltage until the 9-v battery has rotted away. But it draws a continuous current so the battery wouldn't last very long.
Any chance of using a 1.5 volt battery?
RE: zener diode voltage divider
The problem this is just an off-shoot of a larger ciruit. The 9V is needed to run an amplifier so I cannot use a 1.5V battery unless I add this in a almost a seperate circuit but this will take up too much space within the device. I would prefer to use the second option for the reasons that you describe but can't find a 1.5V zener diode. I need a stable 1.5v hence the use of a zener diode.
RE: zener diode voltage divider
TTFN
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RE: zener diode voltage divider
RE: zener diode voltage divider
RE: zener diode voltage divider
Dan - Owner

http://www.Hi-TecDesigns.com
RE: zener diode voltage divider
RE: zener diode voltage divider
RE: zener diode voltage divider
RE: zener diode voltage divider
Many thanks Andrew
RE: zener diode voltage divider
For example, what is your cost bogey? The example here: http://www.national.com/pf//LM/LM2736.html probably runs less than $2. You've already spent that much on this thread.
TTFN
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RE: zener diode voltage divider
RE: zener diode voltage divider
RE: zener diode voltage divider
RE: zener diode voltage divider
If the load is 300µA then you can't use a shunt regulator diode and a 120K resistor (as suggested by operahouse) since the maximum current from that would be 62µA. clearly you need a resistor lower than (9 – 1.5)/300µ = 25K. Typically you would allow at least 200µA for the shunt regulator, but this all depends on how much variation there is in this "300µA" load and how much voltage ripple on the 1.5V rail is acceptable.
Whilst ordinary silicon diodes are not really specified for forward operation as shunt regulators, there is a diode specially designed for this purpose. Example NXP BAS17 is a single diode "stabistor". All it is, is a single silicon diode for operation forward biassed, BUT it gives data for using it in this way which you will not find for an ordinary 1N4148, BAV99 or whatever.
RE: zener diode voltage divider
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If we learn from our mistakes I'm getting a great education!
RE: zener diode voltage divider
RE: zener diode voltage divider
Dan - Owner

http://www.Hi-TecDesigns.com
RE: zener diode voltage divider
I believe you are right. Where did that come from? It wasn't there when I looked last night!
Sorry folks, I'll get my coat...
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If we learn from our mistakes I'm getting a great education!
RE: zener diode voltage divider
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.
RE: zener diode voltage divider
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
RE: zener diode voltage divider
If you go at Digikey, you can find Zener diode as low as 1.8V.
RE: zener diode voltage divider
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If we learn from our mistakes I'm getting a great education!
RE: zener diode voltage divider
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
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...