Bench PSU question

Collapse
X
 
  • Time
  • Show
Clear All
new posts
  • Crystaleyes
    Badcaps Veteran
    • Sep 2021
    • 493
    • Brazil

    #21
    Giving the socket a quick clean and a close look, nothing jumps out at me.

    One other thing, while I remember, is that when the voltage is set to zero, and then the amperage is also set to zero. the voltage goes up to around 5 -6 volts. Not sure if that might be a dodgy pot but a quick test of them shows that the voltage pot goes from 1K down to 1.8 ohms and the amperage pot goes from 10k down to just under 4 ohms.

    Comment

    • stj
      Great Sage 齊天大聖
      • Dec 2009
      • 31139
      • Albion

      #22
      check the tracks from end to end in each pot

      Comment

      • redwire
        Badcaps Legend
        • Dec 2010
        • 3912
        • Canada

        #23
        Where is the output capacitor? You need at least 10-100uF cap at the regulator's output for stability or it can oscillate. It might be doing that.

        A weakness with this PSU design, and every bench PSU has shortcomings... is the for the output voltage to spike up when you shut off power. You can have it set to 5V and then turn it off or a mains failure happens, and the output voltage spikes up and blows whatever you were powering. It's because the 5V rail falls fast (powering LED panel meters) so the control op-amp can't operate but the pass transistor gets turned on full until the big caps discharge on the HV rail.

        Another possible weakness is charging batteries I would guess 12V is the max. but a 24V battery could backfeed and blow parts if the PSU voltage was set low say a few volts, or power outage - and you connect the battery.
        For reverse-polarity protection I just add a big MR756, 6A10 or 10A10 for good smoke and sparks whenever I do that by accident lol.

        Comment

        • Crystaleyes
          Badcaps Veteran
          • Sep 2021
          • 493
          • Brazil

          #24
          Originally posted by stj
          check the tracks from end to end in each pot
          Think I'm just gonna put in some new ones. I have plenty here...

          Comment

          • Crystaleyes
            Badcaps Veteran
            • Sep 2021
            • 493
            • Brazil

            #25
            Originally posted by redwire
            Where is the output capacitor? You need at least 10-100uF cap at the regulator's output for stability or it can oscillate. It might be doing that.

            A weakness with this PSU design, and every bench PSU has shortcomings... is the for the output voltage to spike up when you shut off power. You can have it set to 5V and then turn it off or a mains failure happens, and the output voltage spikes up and blows whatever you were powering. It's because the 5V rail falls fast (powering LED panel meters) so the control op-amp can't operate but the pass transistor gets turned on full until the big caps discharge on the HV rail.

            Another possible weakness is charging batteries I would guess 12V is the max. but a 24V battery could backfeed and blow parts if the PSU voltage was set low say a few volts, or power outage - and you connect the battery.
            For reverse-polarity protection I just add a big MR756, 6A10 or 10A10 for good smoke and sparks whenever I do that by accident lol.
            Thank you for the suggestions. I'll give that output capacitor a go and let you know how it goes. If that works and the voltage stabilises, then I'll give the diode a go too.

            Nice one!

            Comment

            Related Topics

            Collapse

            • Dvsr
              On M-Audio AV40 active studio speaker's two zener diodes get really hot.
              by Dvsr
              Hi. I need help from wiser guys. I am amateur in electronics and can't figure this out by myself.
              I bought faulty speakers, M-Audio AV40's. Other speaker has all the electronics in it and the other speaker is just passive one powered by the other speaker's amp. Original problem with the speakers was loud buzzing. I figured out that there is something wrong with the capacitors. I went ahead and replaced every electrolytic capacitor on the PCB. The caps are good quality and have the same values as the original ones.
              After replacing the caps I started testing out the speaker. It seemed...
              09-10-2025, 10:20 AM
            • caspian
              What Zener Diodes on a Linear Power Supply
              by caspian
              Dear members,

              I have a linear variable power supply with unknown brand name that I used for voltage injection.
              Then it failed. I discovered that its transistors (Q1 and Q2) are shorted.
              In addition, I discovered that its zener diodes are defective.
              I can replace the burned transistors.
              But I do not know the model of the zener diodes. the model number is not marked on the zener diodes.
              Therefore, I cannot replace the zener diodes.
              I do not want to test the zener diodes in a test circuit to discover their model or value.
              no schematics are available...
              05-26-2025, 12:38 PM
            • shamsudeen
              Hi, Can we use SMPS Bench Power Supply for Laptop troubleshooting?
              by shamsudeen
              Hi all, I just need to know that, can i use SMPS type power supply to test and short circuit detection on a laptop motherboard?
              I saw 95% of repair guys are using only Linear bench power supply. linear bench power supply is pricy, thats why i planned to get one SMPS supply.

              i know that in linear power supply the noise will be very low comparing to SMPS supply....
              07-19-2025, 07:14 AM
            • Eniaro
              Bench test a series X
              by Eniaro
              How do you bench test a series X? I was planning to find a defective PSU to use its connector, but before I go about doing this, I was wondering if there's any bench PSU to the series X connector adapter available
              06-17-2025, 01:46 PM
            • Nikolai Danylchyk
              Lenovo T480s usb-c charging port replacement - Knocked off a couple of diodes.
              by Nikolai Danylchyk
              Hi folks. As the title says, I was doing a port replacement on a Lenovo Thinkpad T480s and in the process of post-solder cleaning, I somehow knocked off 2 or 3 diodes (i think they are diodes) near the main usb-c. I can't seem to find what kind of a diode is that. I know it's ultra tiny and just has a letter "G" on it. Would someone maybe have a proper schematic for the t480s model? I can only find the non-s one and it's quite different to the "s". Would love to figure out what component that is.
              Thanks in advance!...
              05-08-2025, 06:18 AM
            • Loading...
            • No more items.
            Working...