It need to supply 6mA @ 5.1V (regulated) to a circuit so I've breadboarded the circuit below to try to determine the value required for the series resistor (Rz) required for a C5V1 Zener diode.
6mA/5.1V = 850Ω so I'm using an 820Ω resistor for test purposes.
According to the datasheets for various C5V 1 zeners I looked at Izt could be 11mA but I am not certain so I thought it would be good to use 20mA for the calculation.
26mA/6.9V = 265Ω so I set my resistor substitution box to 270, connected it as Rz and measured 5.35V across the zener.
From everything I've read about zeners in the last few days that indicated that not enough current was flowing through the zener for it to regulate so I needed to decrease Rz to increase the Iz but when I decreased Rz the voltage across the zener increased.
A bit of experimenting found that the zener voltage is 5.1V when Rz is 960Ω, at which point there is less than 1mA through the zener.
If I increase the Rz above that the voltage decreases and if I decrease Rz the voltage increases.
What am I doing wrong?
6mA/5.1V = 850Ω so I'm using an 820Ω resistor for test purposes.
According to the datasheets for various C5V 1 zeners I looked at Izt could be 11mA but I am not certain so I thought it would be good to use 20mA for the calculation.
26mA/6.9V = 265Ω so I set my resistor substitution box to 270, connected it as Rz and measured 5.35V across the zener.
From everything I've read about zeners in the last few days that indicated that not enough current was flowing through the zener for it to regulate so I needed to decrease Rz to increase the Iz but when I decreased Rz the voltage across the zener increased.
A bit of experimenting found that the zener voltage is 5.1V when Rz is 960Ω, at which point there is less than 1mA through the zener.
If I increase the Rz above that the voltage decreases and if I decrease Rz the voltage increases.
What am I doing wrong?