I know the anode has a + sign and cathode has negative sign. But are these signs reversed depending on how the diode is connected with the circuit?

enter image description here

In the above pic, in fig 4.2b, why isnt the - sign on the top and + sign on the bottom of the diode, since the cathode is on the top side? Also, what does -v indicate in fig 4.2b?

  • \$\begingroup\$ Note that Fig 4.2 (b) violates every known datasheet Absolute Maximum for Vr ( if it were an LED) Although we refer to Zeners as the reverse Voltage -V they are often assumed positive as if you understand it is an absolute value as a component \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Sep 8 '18 at 0:25
  • \$\begingroup\$ Think of the diode as a push/pull type door. From the Push side you can go right threw with no resistance(no voltage drop). From the pull side if you push it blocks you. Now with enough force(Breakdown voltage) you will eventually get through. \$\endgroup\$ – Robert Fay Sep 17 '19 at 20:43

In 4.2b, you have +10V at the top of the circuit, so the cathode must be more positive than the anode. In that case, the diode acts as an open circuit - no current will flow, so there is no voltage drop across the resistor, and 10 volts, with polarity as shown, across the diode.

The + and - signs beside the diode indicate the polarity of the voltage applied to the diode.

| improve this answer | |
  • \$\begingroup\$ why is anode called the positive terminal then? clearly, in that figure, the anode is at a lower potential right? Also, in fig 4.1b, in the graph, what does -v indicate if the voltage drop across the diode is +v? \$\endgroup\$ – David Sep 7 '18 at 23:05
  • 3
    \$\begingroup\$ "Anode" and "Cathode" are the names of the terminals of the diode - they don't change just because you turn the diode around, or the circuit applies a voltage the "wrong" way. You don't call the front of your car "the back" when you are backing up, do you? \$\endgroup\$ – Peter Bennett Sep 7 '18 at 23:11

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.