| Electronics > Projects, Designs, and Technical Stuff |
| Lab power supply over-voltage when turning on |
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| David Hess:
--- Quote from: Chris56000 on June 21, 2019, 08:10:31 pm ---The reason a turn-on overshoot occurs is because the control error amplifier is operative before the rest of the PSU has started to provide a feedback-voltage to it's voltage-control input. --- End quote --- It is not always because the error amplifier is inoperative. It can also be caused by integrator windup in the error amplifier. Some designs do not require anything extra to prevent problems during startup or shutdown. In the example below from a Tektronix PS503A, Q15 and Q115 (marked red) clamp the outputs during shutdown to prevent output voltage spikes (1) but no special precautions were necessary for startup because the reference at Q25 and Q30 (marked green) does not start until the error amplifiers are already operating. The lack of additional external frequency compensation in this design prevents excessive integrator windup. The Tektronix PS501, which is basically the positive half of the PS503A, does not even have the shutdown clamp circuit because there is no negative output to interact with the positive output. (1) (1) I suspect the shutdown clamps were added to the PS503A design after discovering that there was an issue. I doubt they were originally designed in. I do not know if they were in the PS503 because I do not have those schematics. |
| lordvader88:
--- Quote from: pevonous on June 19, 2019, 01:20:05 pm ---Have you tired to open it up and check inside of it, sometimes, there has a problem of MOSFEET issue on it. I don't know if it can help you or not. --- End quote --- I don't know much, but I was thinking a MOSFET too because I had 1 do something similar in a load tester. And also learned better linear PSU's use MOSFET's...can't wait to make 1. But there's other things too, maybe there is no FET |
| Zero999:
--- Quote from: Chris56000 on June 21, 2019, 08:10:31 pm ---Hi! Apart from the hassle of arguing it out with his original Supplier, with all the aggro of waiting for a replacement to be supplied, the OP could well do that and find out the replacement that comes has an even worse overshoot, and the Supplier/OEM denies it's a design fault, which it most assuredly is! --- End quote --- Then send it back again and demand a refund. I know what you mean: fixing something can be educational and rewarding, but it's not the buyer's job to fix a defective product. I also think doing so would be a wrong, since it would allow the seller to get away with selling defective products. Consumers shouldn't have to put up with this crap. |
| Siwastaja:
--- Quote from: Zero999 on June 25, 2019, 10:25:20 am ---I know what you mean: fixing something can be educational and rewarding, but it's not the buyer's job to fix a defective product. I also think doing so would be a wrong, since it would allow the seller to get away with selling defective products. Consumers shouldn't have to put up with this crap. --- End quote --- Yes. IMHO, people are too shy when it comes to completely normal things like making things right by the person/company that fucked it up. I have manufactured and sold things; I have made mistakes; I have never felt bad when they have been pointed out to me, and I'm asked to make it right, in one way or another. It's normal customer service. There are companies and people unable to be responsible, but you don't need to assume that. Assume they want to set it right, and be polite and clear, and most often everything goes well, and you don't need to suffer with faulty products. Unless you genuinely want to see it as an learning opportunity, of course. The same applies to reselling & retail. They are making a profit for a reason. It's part of their business risk that some units fail and come back, and it's their job to communicate it further to the manufacturer. |
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