Understanding Zener Diode Load Currents and Regulation

In summary, this problem is trying to find out what the voltage across the limiting resistor is when the circuit is not in use. If you figure out what the voltage is, you can find out what the current through the resistor is.
  • #1
lemon
200
0
I have to answer this question in front of the class tomorrow. Been struggling all weekend with no joy.

Question:
Determine the minimum and maximum loads currents for which the zener diode on the figure below will maintain regulation. What is the minimum RL that can be used.

Vz=12v, Izk=3mA and Izm=90mA

Please see attached image file.

If I figure the circuit without the load, apparently this will tell me how much the circuit will draw from the 24V power supply. It will still be regulated.
I don't understand this. I'm beginning to feel stupid. When I figure out a circuit with a supply/resistor/zener diode, am I treating this as though it is an ordinary diode in forward bias? And what exactly am I hoping to end up with?

Please see diagram attached.
 

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  • #2
lemon said:
I have to answer this question in front of the class tomorrow. Been struggling all weekend with no joy.

Question:
Determine the minimum and maximum loads currents for which the zener diode on the figure below will maintain regulation. What is the minimum RL that can be used.

Vz=12v, Izk=3mA and Izm=90mA

Please see attached image file.

If I figure the circuit without the load, apparently this will tell me how much the circuit will draw from the 24V power supply. It will still be regulated.
I don't understand this. I'm beginning to feel stupid. When I figure out a circuit with a supply/resistor/zener diode, am I treating this as though it is an ordinary diode in forward bias? And what exactly am I hoping to end up with?

Please see diagram attached.

This is not a difficult problem if you keep in mind that the Zener diode has an almost constant reverse voltage over a range of reverse current. That is what this problem is about, nothing to do with forward conduction. The key is to assume the output is at 12V.

You also know the feed voltage is 24V, and that the series resistor is 470 ohms.

You should be therefore be able to see what the voltage across the 470 ohms is.

Then find the current through the 470 ohms resistor (I=V/R).

You already have the maximum and minimum zener currents, so the rest should be easy.

Finally, wouldn't this be better posted in the "homework section?
 
  • #3
The voltage across the limiting resistor is 12v. Therefore the current through it is 12v/470ohms=25.5mA

You already have the maximum and minimum zener currents, so the rest should be easy.

Please don't assume this, as I am very confused by this.
Izm=90mA
Izk=3mA

Yes. I made a mistake. This should be in homework section.
 
  • #4
ok. so 25.5mA is within the range of the zener diode so the current will flow in reverse bias. This is considering the circuit without a load.
If we attach the load, it will now draw away the current from the zener. The zener cannot get below 3mA or it will not function correctly. So the load (attached in parallel to the zener) must not allow a current below 3mA to flow through the zener diode.
How am I doing. If correct. Now I am stuck
 
  • #5
We have 25.5mA flowing into the node joining resistor, zener, and load.

The zener needs to draw at least Izk = 3mA out of the node

The sum of all currents into / out of any node is zero.

How much current must therefore flow out into the load?
 
Last edited:
  • #6
25.5mA - 3mA = 25.2mA
 
  • #7
lemon said:
25.5mA - 3mA = 25.2mA

Erm, I would think that 25.5mA-3mA = 22.5mA (But note I got that wrong the first time - slippery things,these plastic keyboards!)

Assuming that last was just a slip of the finger, just for interest, what do you think made the problem so difficult in the first place?
 
  • #8
Plastic was it :-
Hay sorry Adjuster. Not very good with cryptic stuff. huh?
 

What is a Zener diode current load?

A Zener diode current load is a type of diode that is designed to operate in the reverse breakdown region, where it can maintain a constant voltage across its terminals while allowing a large amount of current to flow through it.

How does a Zener diode current load work?

A Zener diode current load works by utilizing a phenomenon known as the Zener breakdown, which occurs when a high enough reverse voltage is applied to the diode. This causes a flow of current through the diode, maintaining a constant voltage across its terminals.

What are the applications of Zener diode current loads?

Zener diode current loads are commonly used as voltage regulators in electronic circuits, as they can maintain a stable voltage despite changes in the input voltage. They are also used in overvoltage protection circuits and as voltage references in precision measurement devices.

What factors affect the current load of a Zener diode?

The current load of a Zener diode is affected by the breakdown voltage of the diode, the resistance of the load connected to it, and the power rating of the diode. Temperature can also affect the current load, as higher temperatures can cause a decrease in breakdown voltage.

How do I choose the right Zener diode current load for my application?

When selecting a Zener diode current load, you should consider the desired output voltage, the maximum current and power requirements, and the temperature range of your application. It is also important to choose a diode with a breakdown voltage that is slightly higher than the desired output voltage to allow for variations in temperature and other factors.

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