zener diode usage for regulating of high voltages

[sweethomela8]

Hi,

I'm trying to use a zener diode (18.5V) reverse bias to ground with a source voltage that can range from 9 V to 30 V...I basically want the diode to conduct and regulate the voltage to 18.5 once the voltage gets that high. I'm using a 1 k resistor in series with the source, but get a very small voltage on the output (other side of resistor / zener diode), can anyone explain what may be going on? The current I'm drawing needs to support 2 amps atleast.

 

[kalyanasv]

Well, your using a Zener to clamp a voltage. I suppose your clamping it using a back-to back zener diode. you should have a look at this **broken link removed**.

 

[alexan_e]

Take a look at Tutorial: Transistor-Zener Diode Regulator Circuits

Alex

 

[Miguel Gaspar]

YOU MUST UNDERSTAND THAT ZENER DIODES requiere a minimum current to regulate correctly. And you can't expect that a 18.5 volts form the source the zener diode start the regulation.
For example for a 10Vz diode it is specified Iz = 25mA. You need a voltage greater than 10, in this example 15V.
R in series = (15-10) / 25mA =200 Ohms
So the resistor in series with the zener must be smaller or equal to 200 Ohms.