Novice questions : voltage in a circuit and zener diodes

[bdl]

I'm a novice with electronics, I understand most of the basics but I do have what may be dumb questions:

1) In relation to a circuit, how is voltage maintained? My thinking is that if a component in a circuit requires 3V, for example, and I use two "AA" cells to power the circuit, the power source is a constant and all components always have 3V to use. Or is it that each component "leaches off" a bit so that when current reaches a power critical component (an IC of some sort let's say) in the circuit, it's "cheated" in some way? Do I need to calculate the total circuit power requirement to avoid drop-out? If I do this, and add 5V to the circuit, do I simply need to use resistors to limit power to a certain component?

2) What is a practical, real-world application of the Zener diode vs a standard diode? I've used what I would consider a "regular" diode to prevent reverse current flow, how does this differ from what a Zener diode can offer? Some tutorials use them in circuit design to prevent reverse current, is this the correct use of these diodes?

 

[keith1200rs]

It depends on the application, but most circuitry uses a fixed voltage (or two) and the supply voltage (e.g. batteries) is regulated to that voltage. Provided the circuit is designed correctly that voltage will not vary with the load or as the battery voltage drops.

Zener diodes have a deliberately engineered reverse breakdown voltage. Used in the forward direction they look like normal diodes. Used in the reverse direction they can help to limit voltages. They can be used as crude voltage regulators, voltage references or limiting devices.

Keith.

 

[bdl]

Very good, thanks for the reply, Keith.

 

[steelhacker]

a 1n4742 (12v) zener diode in reverse bias will only allow 12v to pass.

there are zener diodes for just about any voltage that you need.

use a transistor to boost the current capabilities of your regulation circuit.

 

[LvW]

.........
Zener diodes have a deliberately engineered reverse breakdown voltage. Used in the forward direction they look like normal diodes. Used in the reverse direction they can help to limit voltages. They can be used as crude voltage regulators, voltage references or limiting devices.

Keith.

To explain the effect a bit in more detail:
In reverse direction (around the breakdown voltage) due to a very steep current-voltage characteristic there is a very small dynamic (differential) resistance in the order of 1 Ohm. Thus, for changing (unregulated) voltages you can create a voltage divider with a very small output resistance, which is the property of a good voltage source.