I want to make something clear. Most diodes have in their datasheet some current for a given treshold voltage. For example a led will pass 20mA current when 4volts are applied to it. Or a zener diode's minimum turn on current is 10mA when 5,6 volts are applied across it. Does this mean this litteraly means that the zener or the led will pass this current when the minimum turn on voltage is applied across them? I mean for example the led will pass 20mA when you apply 4volts to it. If you have 9volts you would need to add a current limiting resistor because the large voltage will push too big current through the diode and burn it. Is it some kind of refference or standart? In DC motor datasheets there are given two currents for a given nominal voltage. One at no load condition which is the smaller one and with load condition which is bigger. They are given so you can know in case you want to build a bridge for example. Isn't this the same thing? I need to know this because if I were to build a transistor zener voltage regulator I would need to know what current will the zener pass so I can calculate the required base resistor in order to give me the needed base voltage.