Question about using zener diode to set a reference voltage

[Ipanema]

Zener Diode

Hi,

I'm using a zener diode to set a reference voltage of 1.8V. Attached is the datasheet of the zener diode. My circuit consist of a variable current source (upper) connected to the zener diode (lower).

Questions :
1) Can zener diode works by current biasing instead of voltage biasing.

2) In the datasheet (page 3), MMSZ4678T1 breakdown voltage range is between 1.71V to 1.89V at 50uA Izt. What would be the breakdown voltage range for 0~10mA of current? From Figure 9, it shows that the voltage will range from 1V to 2V. How true is this?

3) Pls suggest any other way of generating 1.8V reference from a variable current source.


Thanks.

 

[IanP]

Re: Zener Diode

Answer to question1:
Zener Diode needs some current to behave like a voltage reference. So the answer is: current biasing.

Q2.
The data sheet states that the voltage will be between 1.71V to 1.89V at 50µA current. The same data sheet gives you values of Vf (note this is niot Vz) at 10mA.
This value is for usig this diode as a diode not as Zener Diode, and it is MAX value.

Q3.
Bandgap. Search this forum for answers.

 

[Ipanema]

Re: Zener Diode

Hi IanP,

Thanks for your reply. Pls refer to Figure 9 of the datasheet. It shows the graph of Iz vs Vz. So if my Iz is changing, will the vz changes as well?


Thanks,

 

[IanP]

Re: Zener Diode

Only theoretical zener diode will maintain the same voltage (Vz) over wide range of currents (Iz).
Voltage on a real zener diode will vary for different currents (and is also temperature dependant), and this is the reason why you use constant current source to bias a zener diode..