feedback
Rate this webpage

Need
Support?


Ask An Expert

Our Ask An Expert knowledge base contains answers to questions from designers like you. Browse the knowledge base by category or search key words. Not seeing what you need? Ask An Expert a question of your own.
All   >>  Energy Efficiency   >>   Power Supplies   >>   Questions
 

Reference 1N5333B series Zener Voltage Regulators, specifically 1N5388B (200V, 5W zener). My problem is datasheet versus ohm's law. The datasheet has: At 200V (Vz), I-zt is specified at 5mA. And Z-zt at I-zt is specified at 480 ohms. But why is this not consistant with Ohm's law: Ohms = V/I = 200V/5mA = 40,000 ohms I am trying to limit an unregulated HighVoltage power supply which goes over-voltage, So I want to limit it with zeners. But I don't want the zeners to current-overload my HVPS when the 'safe' over-voltage falls near the rated-voltage output. My application is biasing individual photomultiplier dynodes with individual HVPS for US Navy, NAVAIR. So I really need to know zener-impedance at 5ma, 1mA, 0.1mA. And I also need to know at what voltage does the zener impedance start a significant increase (only a very few zeners on this datasheet show this inflection). So is there data on zener impedance as they approach Vz ? Thank you kindly.

Zzt and Zzk are measured by forcing a 1kHz current into the device centered around the Izt and Izk value listed in the datasheet. The displacement from that current parameter is 10%. For this device, Izt and Izk are 5mA and 1mA respectively. This means that the current used for this test would be a sinusoidal wave form of 5.25mA in the case of Izt and 1.05mA for Izk. The voltage dropped across the diode is then measured, and the impedance of the device is calculated. These parameters are used to give the customer information about the knee of the device. The values for these parameters that are listed in the data sheet are the max impedance specs for the device. We do not have any other data for zener impedance. For limiting of the high voltage from your HVPS you can also consider basic transistor series voltage regulator circuit.Hope this helps. Answered by:
ON Semiconductor
2014-01-28 12:30:20.138