Timeline for How do you size the correct diodes for OR application of two power supplies? [closed]
Current License: CC BY-SA 3.0
16 events
| when toggle format | what | by | license | comment | |
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| May 27, 2016 at 8:18 | history | closed |
Eugene Sh. The Photon Daniel Grillo JIm Dearden user39382 |
Needs more focus | |
| May 25, 2016 at 13:34 | comment | added | user4574 | @Douglas So you have said that the supply feeding the contactor coil is capable of 1.25A, but does the coil actually draw that much current or is it some lesser amount? | |
| May 25, 2016 at 12:00 | answer | added | Olin Lathrop | timeline score: 2 | |
| May 25, 2016 at 11:42 | comment | added | sathyanarayanan | For selection of diode allaboutcircuits.com/textbook/semiconductors/chpt-3/… check this link. | |
| May 24, 2016 at 21:28 | comment | added | Mark | OK, it's not as simple as I first imagined. I think that you are OK, but that's assuming I really understand how you are doing this. A schematic would help. | |
| May 24, 2016 at 20:35 | comment | added | Douglas | @ThePhoton i am looking for the theory behind how to calculate the correct size for a diode. I am not asking anybody to calculate it for me. thanks. 12V power supply with max current of 1.25A from the power supply. Does that mean it is as simple as say 15V 2A diode or increase to 50V 3A Diode what the reasoning behind what diode to choose? | |
| May 24, 2016 at 20:29 | comment | added | Douglas | @Mark im not actually ORing two separate power supplies i am actually ORing two control signals, each of those control signals being a 12V supply from the same power supply. ie I have two relays and the are controlled by other devices, the relays both have a NO contact and when the relays activate the 12V is passed through each of the respective relays. These control signals can be independent or on together and they control a contactor. So either 12v A or 12v B can operate the contactor. I want to have all the "control" signals there are 5 of them OR together with 1 O/P to contactor. | |
| May 24, 2016 at 19:59 | comment | added | The Photon | @Douglas, there is no one size fits all solution. You as the engineer for your system need to evaluate what the normal and maximum load currents are, if there are any transient load currents, what thermal environment the diode will operate in, what lifetime the product needs to have, etc., then choose a diode that meets your requirements. | |
| May 24, 2016 at 19:56 | comment | added | Mark | Why are you trying to OR two power supplies? If it is because one supply does not supply enough current, then you may have issues, as Sparky pointed out. If you are just after redundancy, and a single supply provides adequate current, then you're fine, as long as you can tolerate those voltage variations caused by the diodes. | |
| May 24, 2016 at 19:54 | comment | added | efox29 | @Douglas - use the "@" symbol when referring to users such as what I have done with your name. If you do not, they will not be notified that a comment has been made to them. | |
| May 24, 2016 at 19:46 | comment | added | Douglas | At Sparky,256, how much of an issue is it if one diode dominates? and what does that mean long term? ie will one power supply be more likely to burn up before the other? thanks. | |
| May 24, 2016 at 19:43 | comment | added | Douglas | AT EUGENE : Well, i do actually understand that the diodes need to be sized in relation to voltage and current at the extremes, the question is "How do you size them" and what is a good safety factor? You answer provided zero help. I am looking for a step by step guide which details the "how". If anybody can explain it, it would be appreciated. Professor responses like the above are not helpful at all. | |
| May 24, 2016 at 19:43 | review | Close votes | |||
| May 27, 2016 at 8:18 | |||||
| May 24, 2016 at 19:40 | comment | added | user105652 | Do not assume that both diodes will have exactly the same Vdrop across them unless it is proven by testing. This means that with diode summing junctions, 1 diode will dominate as the current source, even if by a tiny amount. The power supplies will not put out exactly the same voltage either. This will also cause one diode to dominate as the source of current. | |
| May 24, 2016 at 19:07 | comment | added | Eugene Sh. | The voltage and current is determined by the voltage and current expected on these diodes at extreme conditions multiplied by a safety factor. You do the calculations. | |
| May 24, 2016 at 19:04 | history | asked | Douglas | CC BY-SA 3.0 |