Can Diodes be placed without proper resistance?

Question

While looking at circuit schematic of a rectifier, i recalled that i once came across a fine article on diodes that read "diodes offer almost zero resistance to current hence theres a greater possibility that it can burn out at high voltage operation, hence its advisable to use resistors before every power diode" So, does it mean that we should place resistors before diodes or is it just for high voltage operation? if so, how should resistance be matched with every diode?

I'm really confused because the schematics for rectifiers dont show a resistor placed before any of the diodes :-s

Answer 1

The load acts to limit current so in normal application, no resistor is required or desired.

I don't know where that statement came from, but it is false. Unless you misquoted it. For example, this is correct "LED diodes offer almost zero resistance to current hence there's a possibility that it can burn out at higher voltage operation, hence its advisable to use resistors in series with every one"

The resistance is not zero, just low.

edit: the exception is if you put diodes in parallel, you need resistors to equalize the current between them. Usually very small. For example, if you put 5 - 1 amp diodes in parallel, you would use about 0.5 ohms in series with each.  You would still not get 5 amps out of it, perhaps 3 or 4.

Diodes in parallel are never recommended as the negative temperature coefficient tends to cause all the current to flow through 1 diode.  Vf of a diode goes down by 2mv per degree. If one diode started to use more current, it would get hotter, and it's lower Vf would cause even more current to flow, positive feedback, leading to overheating and distruction.

Answer 2

Place resistor in series with rectifier only require when it carries high current and you have limit of choice to obtain high current rated diode. The resistor value is quite small,like 1 ohm or 0.1 ohm to limit the peak current like feeding into very large capacitance (100,000mfd). Or connecting diodes in parellel to increase the current rate ( using 10 diodes rates at 25 amps to obtain 250 amps output to save cost to buy high power diode). For small current application,do not need any resistor in series of diode . Always choose higher voltage and current rated diode at least double or more where the circuit requires.

Answer 3

diodes are used in the billions with out series resistors