I'm trying to build a large dc bench power supply with buck and boost converters - Page 1
Forum section: electronics / projects

author: SKHILLBILLYSlures
author_rank: Regular Contributor
timestamp: July 14, 2017, 03:57:29 pm
content: This is the proposed control circuitry.The idea is to only have one V+ terminal and one ground terminal on the output of the power supply and to control the out put based upon the biasing of the comparator (the power sources that bias the comparator is actually the voltage sense inputs the 80V is the boost module and the 12V is the Buck converter module) I'm using 2of each module in parallel just as the block section indicates

author: SKHILLBILLYSlures
author_rank: Regular Contributor
timestamp: July 14, 2017, 04:16:11 pm
content: https://drive.google.com/file/d/0B2I-dxxrl_-Td3RER0pMRllsRFE/view?usp=drivesdk

author: SKHILLBILLYSlures
author_rank: Regular Contributor
timestamp: July 14, 2017, 04:22:36 pm
content: I have never tried to post a picture on here before with my Google phone which stores the image at around 1MB

author: MK14
author_rank: Super Contributor
timestamp: July 14, 2017, 04:25:01 pm
content: You can't usually just parallel power modules like that, as they won't share the load very well.The way you have got V2 and V5 in your circuit, with 50V and 12V seems a very odd way to draw out your circuit, and must surely be a mistake ?There could easily be more issues, but I will leave it at that for now.

author: SKHILLBILLYSlures
author_rank: Regular Contributor
timestamp: July 14, 2017, 05:38:40 pm
content: They are not a mistake, they also are not actually power source as the symbol suggested they are biasing ( the 12 is constant and the 50v is where I would stick a wire to give the comparator a voltage to bias against) if the 50V is turned down to 9.5V or so the relay is supposed to "trip" I understand how completely odd it is I hate using multi-sim wish I could have used eagle or ltspice which unfortunately I don't know how to use either at this time and would've derrived a much better schematic

author: SKHILLBILLYSlures
author_rank: Regular Contributor
timestamp: July 14, 2017, 07:04:23 pm
content: I had a feeling they probably wouldn't share it very well despite the CC/CV on all four "units" I don't believe that I will ever pull on a full 20amps in either direction this is more of a "throw together"Despite this being the case I still wanted proper control circuitry

author: MK14
author_rank: Super Contributor
timestamp: July 14, 2017, 08:04:05 pm
content: Quote from: SKHILLBILLYSlures on July 14, 2017, 07:04:23 pmCC/CV switching, is not necessarily reliable enough, and may lack too much quality (e.g. too slow to respond, overshoot, etc). To allow power sharing like that, in practice. Even though in theory, aperfectCC/CV device, might be able to do it.Your unconventional (to at least me), way of introducing the voltages (such as 50V), into the circuit. Makes it harder for me to help you here. Maybe someone else here, will be much less thrown by that way of doing it, so they can help you.If it was me, I'd probably use opto-isolators, to transfer the information between the separate supplies, and the control circuitry. Hence avoiding a lot of the possible problems, if you don't use them. I'm NOT sure if there are any common grounds between the different power supplies, and the control circuitry.

author: SKHILLBILLYSlures
author_rank: Regular Contributor
timestamp: July 20, 2017, 12:59:41 am
content: Oh my ,terrible mistake. I was so busy today I forgot to mention that the modules do share ground connections. And that the sense input the 50v is the sense positive and the other sense wire is connected to control circuit groundif I were to use opto-isolators to transfer the information in what fashion (I'm sorry to ask you to go out of your way but a schematic would be seriously helpful I'm very visual with some things) we haven't really used those (opto-isolators in class)I wrote this post a while ago school has recently let back in session

author: MK14
author_rank: Super Contributor
timestamp: July 20, 2017, 01:24:42 am
content: Opto-isolators allow you to connect up different circuits. When they are used, things are normally electrically not connected together, in anyway. between the two sides of the opto-couplers/isolatorsThey can help protect your circuit from higher voltages.http://www.electronics-tutorials.ws/blog/optocoupler.htmlIt can also be done, in some cases, by using sensible resistor values, to monitor the different voltages. But that needs to be carefully/properly designed into your circuit. Otherwise, you could easily break your low voltage circuit elements.Since your things share ground connections (to an extent I'm not fully clear about), you can't really draw your schematic like you have. The ground related things need to all stem from the same ground. Just plonking things in the middle of the circuit, like you have is likely to be wrong, and very confusing.You are free to leave it like it is. But doing so, may mean that very few people can ever help you with it.

author: MK14
author_rank: Super Contributor
timestamp: July 20, 2017, 01:30:09 am
content: Also, voltages at or above 30V/50V can be high enough to cause serious injury or kill someone (because of the potentially dangerous currents, through the human body). So I'd totally avoid such voltages, until your electronics capabilities are good enough to safely do stuff like that.Best to stick to 5V or 12V, and other low voltages until your abilities and experience improve.