Below is a voltage regulator circuit for which I measured Vo and Io over a range of load resistance values. Why is there a slight drop in Vo when Io is increased, does it have something to do with the 1N5232B zener diode? (Vdo = 0.7 V, Vz = 5.6V).

Voltage Regulator circuit

enter image description here

  • \$\begingroup\$ As in your previous question, you have omitted the Zener diode breakdown voltage. Can you edit your question to include it? You should also number all the components so that we don't have to refer to "the resistor on the right over the variable resistor". "R2" would be so much easier. \$\endgroup\$ – Transistor Oct 12 '19 at 20:08
  • \$\begingroup\$ I have described the different diode voltages, sorry about that. Also, you could just name resistors by their values. \$\endgroup\$ – Hector Oct 12 '19 at 20:15
  • \$\begingroup\$ Standard Zener diode voltages are 3.9V, 4.3V, 4.7V, 5.1V, 5.6V. It appears that yours is perhaps 5.1V or 5.6V (not 4.0V). \$\endgroup\$ – glen_geek Oct 12 '19 at 20:24
  • \$\begingroup\$ I apologize, it is 5.6V \$\endgroup\$ – Hector Oct 12 '19 at 20:28
  • \$\begingroup\$ @jsotola Thanks for the feedback, will keep in mind. \$\endgroup\$ – Hector Oct 12 '19 at 20:41

That's behaving more like a 5.1 V Zener. At zero output current the voltage is a little over 5.1 V. At 3 mA it's about 5.1 V.

Once you draw more than 4 mA the voltage drop across the 1k resistor will be > 4 V so the output voltage will drop.

I recommend that you double-check the part number and specification. If you're sure it's a 4 V Zener (although your test measurements say that it's not) then add the part number and link to datasheet into your question.

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  • \$\begingroup\$ I apologize, the diode is an 1N5232B Zener with 5.6 V. I have edited the question. \$\endgroup\$ – Hector Oct 12 '19 at 20:28

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