| Electronics > Beginners |
| Zener's burning out |
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| mikerj:
--- Quote from: lordvader88 on July 20, 2019, 06:47:30 am --- --- Quote from: Vgkid on July 19, 2019, 03:46:47 pm ---Schematic, what value of current limiting resistor are you using? --- End quote --- It's on page 11/12 http://www.introni.it/pdf/Farnell%20-%20L%20series%20Bench%20Power%20Supplies The 470 ohm resistor passes around 32mA Z4, the 5V1 is what burns out. One time, P1 also burnt out. It normally is locked around 1mA, I admit IDK how the feedback loop toasted it. --- End quote --- Where are you pulling these numbers from? Given your recent thread I can take a pretty good guess... Z4 is a 1N823 6.2V Zener to start with, and the current through the 470 ohm resistor is set by Z3, a 5.1v zener on the other side of the current mirror: 5.1/470 ~ 10mA. This is the maximum that should be passing through Z4, since some of the current will be going into P101/P102. |
| bd139:
I see the problem here: 1. Circuit copied verbatim without understanding it. 2. Circuit something from the middle ages to start with (Farnell power supplies usually are - decent supplies however). 3. Cargo cult developing. Solution: 1. Go back to basics and understand the problem. 2. Get art of electronics and the learning the art of electronics book (both are on library genesis if you're a cheap arse) 3. Work through the whole damn thing until after lab 11. 4. Consider oneself hit with the clue stick. Short cut as I know it'll be taken: 1. Get an LM723 in and use a circuit off the datasheet. 2. Build the supply around that and an external pass transistor. 3. Admit that it's a cargo cult. Some advice: building a bench power supply is much much harder than it looks. Even all the semi sexy looking designs on here and a lot of commercial units are full of stupid flaws. Overshoot, spontanous oscillation, failure prone (try charging a car battery up with that Farnell supply and then the line power fails!), all sorts. Even an LM317 can oscillate like hell if you happen to have a couple of metres of test leads hanging off it. |
| thinkfat:
LM723 is actually not such a bad choice. You can make quite decent power supplies with it if you combine it with some power transistors. Gesendet von meinem Nokia 6.1 mit Tapatalk |
| bd139:
Yeah it's a VERY nice IC despite being 50 years old this year. It's still going strong. |
| tggzzz:
Snipped a reasonable analysis of PEBCAK... --- Quote from: bd139 on July 20, 2019, 10:34:04 am ---2. Get art of electronics and the learning the art of electronics book (both are on library genesis if you're a cheap arse) --- End quote --- First time I have bumbled into this: --- Quote ---Sorry, this page is not available through Virgin Media Virgin Media has received an order from the High Court requiring us to prevent access to this site. For more information about the order and your rights, please click the relevant link below. --- End quote --- Suppose I'll have to investigate how to avoid that, presuming they aren't using deep packet inspection. |
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