Answer to Question #241379 in Electrical Engineering for Blaze

Question #241379
1-9 We have two Zener diodes with silicon material, Uzl 6V, Uz2 = 9V. When they are used in series in the circuit, determine all the possible voltages we can get. And how about the possible voltages when they are used in parallel? 1-10 Zener diode circuit is shown below, Uz = 6V =10mA, max dissipate power PzM 500ohm Izmin = 200mW, current limitation resistance R Try to determine: 1). When U-20V, R, - 12 Uo = ? 2). When U,-20V, R, =1002 Uo ? 3) when -20V, R regularly? can the Zener diode work 4) when U-7R, is varying, can the Zener diode work regularly? Uo 1-29 1-10
Expert's answer


A silicon material, Uzl 6V, Uz2 = 9V

Consider the above example where V1 is not equal to V2. Here the two voltage sources of unequal magnitude are connected to the same load. Let us say the sources are not ideal and are having some internal resistance. V1 has internal resistance of R1 and V2 has internal resistance of R2. So now apply the superposition theorem across load resistance R to find the total current flowing through each source. Before writing the current equations let us say that I1 is current when V1 is acting alone in the circuit and same I2 when V2 is acting alone in the circuit.

Now, it will look somewhat like this if you apply superposition theorem with V1 acting alone in the circuit and you can redraw the circuit for V2. Solving for I1 you will get

I1 = V1 x [R1+ (R2 || R)] x R2/(R2+R)

Similarly I2 = V2 x [R2+ (R1|| R)] x R1/(R1+R)

We can clearly see the value of two currents obtained are not equal that means there will be some amount of current circulating in between the two sources and one source will become load to the another source which we certainly do not want.

Possible voltages for the Zener Diodes:

when U-20V, R, - 12 Uo =  voltage drop across each is just the total voltage of the circuit divided by the number of resistors in the circuit, or 24 V/3 = 8 V.

When U,-20V, R, =1002 U z=834Ω,Irms=83420​=0.024A

When -20V, R regularly? Here the volateg will remain the same

Can the Zener diode work : Yes, Zener diode work can work

When U-7R, is varying, can the Zener diode work regularly? Uo 1-29 1-10

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