How Does a Zener Shunt Regulate for Drop in Voltage?

In summary, in a zener shunt circuit, the zener diode conducts or "shunts" when the source voltage exceeds its breakdown voltage. The regulator does not compensate for a drop in source voltage below its nominal value, so it is the designer's responsibility to ensure the source voltage is always greater than the zener breakdown. This can be achieved by using current limiting and calculating the current draw based on the difference between the raw voltage and the zener voltage. If the load draws more current than the calculated value, the zener will turn off and the circuit will lose regulation. In case of a voltage dip, the current draw will decrease and the circuit will lose regulation at a lower current draw than before.
  • #1
fonz
151
5
In a simple zener shunt circuit consisting of a zener diode in parallel to the input voltage and load how does the regulator compensate for a drop in input voltage?

In other words the zener will conduct or 'shunt' when the source voltage exceeds the breakdown voltage of the zener diode. How does it compensate for an drop in source voltage below nominal?

Regards
Dan
 
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  • #2
It doesn't. It's up to the designer to ensure the source voltage is always greater than the zener breakdown, if you want it to be regulated by that zener. Also ensure some current limiting so zener power rating is never reached.
 
  • #3
In shunt regulator using zener, say you have a raw voltage of 10V and you put the -ve to ground and and resistor R from +10V to the anode of the zener or 5.1V. The current draw would be I(total)=(10-5.1)/R. If you use this to generate the 5.1V to drive, as long as the load don't draw close to I(total), then you get regulation. Once you draw more than I(total), the zener will turn off and you totally loss regulation.

With this same idea, if you raw voltage dip, then I(total) will drop, using the explanation above, you can draw less current before you loss regulation.
 

1. How does a Zener shunt regulate for drop in voltage?

The Zener shunt regulator works by using a Zener diode in parallel with a load resistor. When the voltage across the load resistor drops, the Zener diode begins to conduct, effectively shunting the excess current away from the load. This maintains a constant voltage across the load, thereby regulating for the drop in voltage.

2. What is the purpose of a Zener diode in a shunt regulator?

The Zener diode is used to maintain a constant voltage across the load by conducting excess current when the voltage drops. It essentially acts as a voltage reference, ensuring that the voltage stays within a specific range.

3. How is the voltage across the load regulated by a Zener shunt?

The voltage across the load is regulated by the Zener shunt by adjusting the amount of current that is shunted away from the load. As the load voltage drops, the Zener diode conducts more current, effectively keeping the voltage across the load constant.

4. What are the benefits of using a Zener shunt regulator?

One of the main benefits of using a Zener shunt regulator is that it can provide a stable output voltage, even when the input voltage fluctuates. It also has a simple and inexpensive design, making it a popular choice for voltage regulation in many electronic devices.

5. Are there any limitations to using a Zener shunt regulator?

While a Zener shunt regulator is effective in maintaining a constant voltage across a load, it is not suitable for regulating large currents. It also has a limited voltage range and may not be able to regulate for large drops in voltage. Additionally, the Zener diode may be damaged if the input voltage exceeds a certain level.

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