Secure Voltage Regulator - Page 1
Forum section: electronics / projects

author: eKoh
author_rank: Newbie
timestamp: April 29, 2017, 07:39:59 am
content: Hello guys!! I am currently designing a little voltage regulator but I want it to make it really safe. Recently I burn a 30$ component in a PCB I made and I don't want it to happen againI have made this out so far:Thespecsthat I am looking for are these:* Short circuit protected* Reverse voltage protected* Low heat dissipation from the regulator- See, I was using a 7805 because I need +5V. Since I am using a Kinetis KL25z for my project, it has a Voltage Input from 5v-9v so, I am planning to feed it with +9v using a 7809 and from the Kinetis there is a pin with +5v so I can feed my other componentes with that. I read that the heat comes because the regulator is not efficient, because going from 12v to 5v, there is a (5/12)*100% = 41.67% of efficiency, and the other 58.33% converts to heat. By changing to a 7809, I am getting a better efficiency: 75%, so "only" 25% goes in heat. Well that's what I think. I have not made any practical testing bydoing so.Correct me if I am wrong!- I was also thinking on adding aLimiter Resistancein series to the input Voltage of the regulator, so that the consumed watts, lower. So there will be less heat, but I am not sure if that's really OK.If my system need more current, will my battery be able to give that?* Solve random functionality by adding Capacitors- I was having some "random functionality" from the XBee S2C Pro when I turned off and on the system. I had to put a 470uF (just random value) Capacitor from V+ and GND, and it kinda solved it (Not the 100% of the times I turned it on it worked). But I know that this is not the best solution.What is this problem about?Btw, I know that the Capacitors fix the ripples from the battery but I am not sure if this is what causes the problem.Well, that's all atm, if you guys have any recommendations or see any problem.Please tell me=)!Have a nice day=)!P.D. By the way, I was thinking on adding a Zenner Diode of 8.2v more less, to the Vo, so that the Kinetis doesn't risk a lot, but I am not sure how to add it, I put a Resistance in series in the output and the Vz in parallel, is that just fine?

author: pelule
author_rank: Frequent Contributor
timestamp: April 29, 2017, 10:34:48 am
content: I am missing some security functions:1) overvoltage protection (needed, if the supplied circuit is sensitive against voltages higher as the nominal value)2) Current foldback (reduce to secure low current, if the current of supplied circuit goes over the defined limit)3) Inverse polarity protection (if by accident you connect a power source to the outputs, but with inverse polarity)/PeLuLe

author: Ian.M
author_rank: Super Contributor
timestamp: April 29, 2017, 11:28:38 am
content: You'll probably want a TL431 crowbar circuit to save your load if the regulator fails shorted. See figs. 24 & 25 in its datasheet:https://www.onsemi.com/pub/Collateral/TL431-D.PDF

author: tecman
author_rank: Frequent Contributor
timestamp: April 29, 2017, 02:23:19 pm
content: For ultimate protection you need to add 2 diodes. One from pin 3 to ground, reversed biased. That will protect the regulator from reverse voltage applied to the output. The other diode is from pin 3 to pin 1. A recommended protection to prevent the output voltage from exceeding the input, which can kill the regulator. A common issue is a cap on the output. You remove the input power and the cap will supply voltage to the output higher than the input and kill the regulator.You might also want to increase C1 for stability.Paul

author: Zero999
author_rank: Super Contributor
timestamp: April 29, 2017, 02:42:24 pm
content: Quote from: eKoh on April 29, 2017, 07:39:59 amWell, whatever you do, i.e. adding resistors, zeners in series with the input, with a linear regulator, the efficiency can be no greater than the ratio of the output and input voltage. The only way to get any better is to use a switched mode regulator.And no one can tell you whether your battery can handle it or not because you've not said how much power you need or the size of your battery.