High Power Zener Diodes - Page 1
Forum section: electronics / beginners

author: sonnytiger
author_rank: Frequent Contributor
timestamp: March 18, 2015, 04:24:40 pm
content: What are they used for? I have this nice Motorola 1N4559 part from the mid 70s and was just curious.http://pdf1.alldatasheet.com/datasheet-pdf/view/114757/MOTOROLA/1N4559.html

author: JohnnyBerg
author_rank: Frequent Contributor
timestamp: March 18, 2015, 04:42:26 pm
content: Quote from: sonnytiger on March 18, 2015, 04:24:40 pmnot are, whereQuoteShunt regulator?

author: SeanB
author_rank: Super Contributor
timestamp: March 18, 2015, 04:53:27 pm
content: High power zeners are typically used as either a shunt regulator or as overvoltage protection. You would use the above 50W zener to regulate a voltage rail where you need high current but have a supply that needs a minimum load to operate. They would be used with the output of say a solar panel to limit the voltage output, or with a thermoelectric generator so that you do not exceed the voltage rating of the supply or the load.Often used in older power supplies to clamp overvoltage so that the built in resistance of the supply ( pass transistor with a series resistor so if the transistor goes short circuit the zener is still within limits) will limit current so the load will not have a hgh voltage even if the PSU fails shorted.Typical in aviation as clamps on power rails, from 400Hz transformers with linear supplies, as a failed supply ( typically a shorted pass element) will not fail the equipment totally, but it will still operate with possibly a thermal warning or a supply monitor showing overvoltage just out of limits, to tell you it is in a failing condition. Still runs but will flag a "change me on the ground" warning instead of stopping a critical system in mid flight, which typically means the landing will be very unplanned and lacking in control.

author: sonnytiger
author_rank: Frequent Contributor
timestamp: March 18, 2015, 05:15:38 pm
content: Ahh that makes sense, thanks for the info! I got it out of an old fluke meter calibrator, no date code but the rest of the parts are from the mid 70s.In short it is a fail safe mechanism or even a fail... working mechanism?

author: SeanB
author_rank: Super Contributor
timestamp: March 18, 2015, 05:49:26 pm
content: Provided the overload is not too much the failure mode from moderate overheating ( 200c or so) is the metallisation on the surface and the internal PN junction migrate through the silicon slice till it diffuses out the back, shorting the device with a low resistance mostly resistive layer. High power and high current it blows the lead wires inside open circuit.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 18, 2015, 05:52:42 pm
content: Primarily an historical abberation; in the veeeery old days, the regulation (change in supply voltage for a change in load current) was improved simply by heavily loading it with ballast resistors. Extremely wasteful, but achieves its goal (the output resistance is reduced at least by the amount connected in parallel, but usually better than that, due to the nonlinear resistance of the rectifier). Later, gas discharge tubes were used as shunt regulators, then as voltage references for the now-familiar pass regulator configuration.Early semiconductor circuits used zener diodes as shunt regulators, typically "boosted" with a pass transistor; but sometimes the zener would be used directly, even for fairly high currents. I wasn't around back then, but the reasons above sound as good as any.Tim

author: sonnytiger
author_rank: Frequent Contributor
timestamp: April 09, 2015, 11:14:37 am
content: Interesting, I don't think I fully understand how it can be used as a regulator by itself or with a transistor, but it seems like the bond wires almost act like a fuse as well, in the case of short circuits. Just an aside.

author: madires
author_rank: Super Contributor
timestamp: April 09, 2015, 11:26:35 am
content: How to create your own power zener:http://www.bristolwatch.com/ele/zener_power_supply.htm