Zener voltage controlled circuit design

In summary: IZ).In summary, the conversation discusses a problem with a zener diode circuit and how to maintain a desired current range. The current law must be obeyed and the equivalent resistance of the circuit must be considered. The value of the current stays unchanged and the zener must be conducting at all times. However, there is a discrepancy in the specifications for the zener and the resistance of the diode (rd) varies in the breakdown region.
  • #1
bl965
18
0

Homework Statement



assn2_5.png

Homework Equations


V0=Vsrz/Rs+rz+VzoRs/Rs+rz-ILrzRs/rz+Rs

The Attempt at a Solution


I formulated 4 cases for voltage inputs of 11 and 13.6 V and 0 to 100 mA. The zener current has to be between 3 and 30mA or 103 and 133mA. How can the current be maintained in thes two ranges? does the diode stop conducting?
Thank you.
 
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  • #2
bl965 said:
I formulated 4 cases for voltage inputs of 11 and 13.6 V and 0 to 100 mA. The zener current has to be between 3 and 30mA or 103 and 133mA. How can the current be maintained in thes two ranges? does the diode stop conducting?
Thank you.

Take some extra care about the distinction between current passing through zener diode and current through radio. What rule do you have to apply? Which current value (min vs. max), considering both branches (zener - load), are you interested in, in order to conclude about what is asked?
 
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  • #3
QuantumQuest said:
Take some extra care about the distinction between current passing through zener diode and current through radio. What law do you have to apply? Which current value (min vs. max) considering both branches (zener - load) are you interested in in order to conclude about what is asked?
The current law must be obeyed. If the radio does not draw the current it must pass through the zener. How can this be possible if the zener cannot handle more than 30 mA?
 
  • #4
bl965 said:

Homework Equations


V0=Vsrz/Rs+rz+VzoRs/Rs+rz-ILrzRs/rz+Rs

Did you forget some brackets in this equation? It cannot be read at all.
It looks as if you add a voltage to a resistance .
 
  • #5
bl965 said:
The current law must be obeyed. If the radio does not draw the current it must pass through the zener. How can this be possible if the zener cannot handle more than 30 mA?

If radio does not draw any current, what is the equivalent resistance of the circuit? Is the value of the current staying unchanged?
 
  • #6
If the radio does not draw any current, than the circuit is the battery, the resistor and the Zener. The current would not change. When learning forward bias diode voltage regulation, when the load changes current, that change is added or removed from the diode and the change in voltage is calculated as current times rd, but in this problem rz is not given. How is rzcalculated?
 
  • #7
LvW said:
Did you forget some brackets in this equation? It cannot be read at all.
It looks as if you add a voltage to a resistance .
V0=Vsrz/(Rs)+rz+VzoRs/(Rs+rz)-ILrzRs/(rz+Rs)
 
  • #8
bl965 said:
If the radio does not draw any current, than the circuit is the battery, the resistor and the Zener. The current would not change. When learning forward bias diode voltage regulation, when the load changes current, that change is added or removed from the diode and the change in voltage is calculated as current times rd, but in this problem rz is not given. How is rzcalculated?

I'll state what I previously said, in another way. Take Ohm's Law. Suppose you have the same car battery. If you change the total resistance of the circuit in no matter what way, does the current stay unchanged?

EDIT: After the answer to this, think about zener, what it achieves and how regarding Ohm's Law.
 
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  • #9
bl965 said:
does the diode stop conducting?
The zener must be conducting at all times, otherwise the circuit is not regulating. Here, you are told that the zener current must at all times be at least 3mA. That's its minimum; and the zener current will jump to a high value when the load is switched off.

The calculations are simplified in this question because you can consider rz = 0 Ω
 
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  • #10
bl965 said:
How can this be possible if the zener cannot handle more than 30 mA?
Now right there we have a problem. [emoji79]

It looks like a mistake in their specs for the Zener, if we assume RL is supposed to be representing the radio---in which case you'll have to ignore what they imply is IZmax
 
  • #11
bl965 said:
When learning forward bias diode voltage regulation, when the load changes current, that change is added or removed from the diode and the change in voltage is calculated as current times rd,

But the resistance of a diode (rd) operating in the breakdown region varies. The voltage drop will be fairly constant over the design range of diode current.
 
  • #12
rd being the Zener's incremental resistance at the operating point
 

Related to Zener voltage controlled circuit design

1. What is a Zener voltage controlled circuit?

A Zener voltage controlled circuit is a type of electronic circuit that uses a Zener diode to regulate the voltage. The Zener diode is designed to have a specific breakdown voltage, which allows it to maintain a constant voltage output even when there are changes in the input voltage.

2. How does a Zener voltage controlled circuit work?

A Zener voltage controlled circuit works by using the Zener diode's breakdown voltage to regulate the voltage. When the input voltage exceeds the breakdown voltage, the Zener diode conducts and maintains a constant voltage output. This allows for a stable and regulated voltage output.

3. What are the advantages of using a Zener voltage controlled circuit?

One of the main advantages of using a Zener voltage controlled circuit is its ability to maintain a constant voltage output, even with changes in the input voltage. This makes it useful for applications where a stable voltage is required, such as in power supplies, voltage regulators, and battery charging circuits.

4. How do you design a Zener voltage controlled circuit?

Designing a Zener voltage controlled circuit involves selecting the appropriate Zener diode with the desired breakdown voltage, as well as choosing the appropriate resistors to achieve the desired voltage output. It is also important to consider the maximum power dissipation of the Zener diode to ensure it can handle the required current.

5. What are some common applications of Zener voltage controlled circuits?

Zener voltage controlled circuits are commonly used in power supply circuits, voltage regulators, and battery charging circuits. They are also used in electronic devices to protect against voltage spikes and overvoltage conditions. Additionally, they can be used in analog-to-digital converters to provide a stable reference voltage.

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