why does zener regulator reduce ripples but can't omit them?

[Super Mario]

^^

 

[Agent 009]

What do you need exactly as information? The way zener diodes work, or their effect on the circuit's output, or what?

 

[Super Mario]

What do you need exactly as information? The way zener diodes work, or their effect on the circuit's output, or what?

The way the zener works in power supply

 

[mozikluv]

zener diodes

hi super mario,

you said how does a zener diode work in a power supply, well let me explain as simplest as i can describe;
1. the main function is it outputs your desired voltage
2. it reduces ripples
3. its output voltage is steadier than an unregulated output
4. it has less power loss
5. it also prevents sudden power surges

there are several ways on how a zener diode is used or connected in a regulated circuit, to name a few;
1. zener diode is shunted on a dc output
2. zener diode controlled transistor regulator
3. feedback transistor voltage regulator

hope this will enlighten you

 

[Ravi]

Let me contribute with some of the practical hints.

Zeners may be connected in series to obtain higher voltages.Example, a 15.9V reference can be produced by connecting a 6.8V zener in series with a 9.1V zener.
You will have to take care to ensure that zeners operate within their rated power dissipation.
Zeners generally perform best when rated at voltages of between 5V to 6V.Therefore, to get optimum performance, reference voltage sources based upon zeners should utilise components which have sener voltages of between 5.1V to 6.2V.If necessary, an external circuitry could be used to provide voltage amplification.
Zeners can generate a significant amount of noise and in application which involve significant voltage gain (such as stabilisation of an amplifier bias supply) it is essential to provide adequate decoupling. Sometimes a parallel connected cap. of between 1 to 100 micro F.will sufficient in most applications.

 

[Super Mario]

Thank you both,
but i still want to know why ripples can't be completely omitted and they're just reduced.......thanks

 

[Roff]

When you make a simple shunt regulator with a zener, you generally have a series resistor from a higher voltage to supply current to the zener and to the load ( the circuit that uses the stabilized voltage). A zener does not have zero resistance. What this means is that a change in current through the zener will still cause a small change in voltage. This means that if there is ripple on the unregulated supply, some of that ripple will still show up on the zener.
Think of a real zener as an ideal zener in series witha low-value resistor. The value of this resistor depends on the type of zener and the current through it, but it will generally be in the range of a few ohms to a few tens of ohms.
The bottom line is, you still have a voltage divider between the current-limiting resistor and the zener resistance. For example, if you have a 1k resistor for current limiting, and the zener's resistance is 10 ohms, about 1% of the ripple on the unregulated supply will show up on the zener.

 

[Super Mario]

When you make a simple shunt regulator with a zener, you generally have a series resistor from a higher voltage to supply current to the zener and to the load ( the circuit that uses the stabilized voltage). A zener does not have zero resistance. What this means is that a change in current through the zener will still cause a small change in voltage. This means that if there is ripple on the unregulated supply, some of that ripple will still show up on the zener.
Think of a real zener as an ideal zener in series witha low-value resistor. The value of this resistor depends on the type of zener and the current through it, but it will generally be in the range of a few ohms to a few tens of ohms.
The bottom line is, you still have a voltage divider between the current-limiting resistor and the zener resistance. For example, if you have a 1k resistor for current limiting, and the zener's resistance is 10 ohms, about 1% of the ripple on the unregulated supply will show up on the zener.

wow thank you very much!
I have a basic electronics book but it doesnt explain that in details,so what book(s) do you suggest I should get?