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Power supply build quality pictorial. part 2

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    Re: Power supply build quality pictorial. part 2

    Geez! Forgot one even larger difference. MJE13009-clones (originally it was a Motorola part; not sure if On Semiconductor, who bought Mot's discretes, still makes the part) are bipolar transistors. TO-247/TO-3P switch devices in power supplies are likely to be MOSFETs.

    Much, maybe most, of the power dissipation in a switch device - transistor or MOSFET - is during the switch time. During switching the device is conducting significant current at the same time there is significant voltage across the device. Power = (Voltage x Current). The slower the switch time, the more power dissipated during each transition; the greater the % switch time is of the entire cycle time, the higher the over all dissipation of the device.

    A bipolar transistor switches far slower than does a MOSFET. Consequently, a transistor dissipates more power during a transition than does a MOSFET, assuming both are of similar current rating and properly driven. At the same switch frequency, a bipolar transistor will dissipate more power than will a MOSFET.

    Looked at another way, if you know the maximum power power you can allow your switch device to dissipate and assuming the same output power, the maximum switch frequency at which a bipolar transistor can be operated is lower than the maximum frequency for a MOSFET. Why would one want a higher switch frequency? The magnetics for a given power level at 50KHz are smaller than for 200KHz, The P/S could be smaller, the heatsinks could be larger, or the resistance to airflow could be less (which allows considerable flexibility to the system designer). Also, filtering conducted noise at 200KHz tends to be less difficult than at 25KHz or 50KHz (BTDT, got a drawer full of T-shirts!)
    PeteS in CA

    Power Supplies should be boring: No loud noises, no bright flashes, and no bad smells.
    ****************************
    To kill personal responsibility, initiative or success, punish it by taxing it. To encourage irresponsibility, improvidence, dependence and failure, reward it by subsidizing it.
    ****************************

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      Re: Power supply build quality pictorial. part 2

      Originally posted by tom66 View Post
      In general you can exceed the Vbreakdown of a diode without damage (avalanche breakdown), but you will cause extreme power dissipation if it is continued for more than a few ms. Which is why they blow up. Isn't the Dell 3008 monitor well known to have issues with 170V diodes going short? On just a 24V supply?
      The originals were 100v or 120v IIRC. 170v diodes make the thing work fine again.

      Originally posted by Wester547 View Post
      I've seen many manufactures put 100V-200V+ (sometimes more) diodes (or schottky rectifiers) on the +12V rail... is that dangerous?
      No, it is "just making sure". It is overspec'ing to some degree, but i believe the main reason 100v diodes are used is that they are industry standard and very cheap in large quantities, for example the MBR20100CT is what's called a "jellybean part" - you can find it anywhere. As for 200v ones - were you talking about the FR302s commonly used in the diodes-on-a-bracket thing for 12v? Cheap cheap cheap.

      A 60 volt diode would be just fine, if they were overspec'ing, they would be better off overspec'ing the current rating instead, that way it wouldn't blow up anymore.

      Originally posted by PeteS in CA View Post
      not sure if On Semiconductor, who bought Mot's discretes, still makes the part) are bipolar transistors. TO-247/TO-3P switch devices in power supplies are likely to be MOSFETs.
      On Semi still makes 13009s, i bought some new ones a couple weeks ago. Fairchild also makes them, and a large number of knock-off manufacturers too. Pretty much everyone and their dog makes them. Fairchild makes them in TO-247 too, named J13009 (FJP13009), but they seem to be unobtanium from any reputable vendor, so i scavenge them from ATX PSUs. I've seen them on ebay tho.

      The cheap halfbridge ATX designs on the market haven't changed in 10+ years. They're still using bipolars. Apart from the 13009 there are some more TO-247 bipolars used in such things, like D209L (2SD209L), and a few more that don't cross my mind right now.
      Originally posted by PeteS in CA
      Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
      A working TV? How boring!

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        Re: Power supply build quality pictorial. part 2

        Originally posted by Th3_uN1Qu3
        A 60 volt diode would be just fine, if they were overspec'ing, they would be better off overspec'ing the current rating instead, that way it wouldn't blow up anymore.
        But is a well-designed PSU likely to short or blow up if 200V+ (if not double that) rectifiers are used on the +12V rail? ^^; Or is this only a threat for PSUs that can barely do their labeled rating if even that, or just lower-wattage PSUs? And I didn't mean diodes-on-brackets, I meant, like, two BYQ28E-200s (10A/200V per part).

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          Re: Power supply build quality pictorial. part 2

          It's the current rating that matters, increasing the reverse blocking voltage won't change that. As Th3_uN1Qu3 said above, the voltage from the transformer output isn't anywhere near that.

          @Th3_uN1Qu3: ST also makes TO-247 13009s.

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            Re: Power supply build quality pictorial. part 2

            ^
            I recently blew a few ST 13009s in TO-247 up. It took just over 400W, though.
            I love putting bad caps and flat batteries in fire and watching them explode!!

            No wonder it doesn't work! You installed the jumper wires backwards

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              Re: Power supply build quality pictorial. part 2

              Check out this absolute trash of a power supply. Pretty sure it's a Deer, all caps are YC and EVERY SINGLE cap on the secondary is bulging. Can you imagine the ripple coming out of this thing before it died? You can't see very well because I had to take a picture of this with my phone at work, but the PCB on the secondary is a very dark brown, a lot of things burned up. This thing took out the motherboard and the RAM when it died. The owner was insanely lucky that her hard drive didn't get killed cause she said she had 60,000 pictures on it and none of them were backed up....
              Attached Files
              Last edited by Pentium4; 09-02-2012, 03:16 PM.

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                Re: Power supply build quality pictorial. part 2

                The small ones are not bulging?
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                  Re: Power supply build quality pictorial. part 2

                  Originally posted by Behemot View Post
                  The small ones are not bulging?
                  haha I'm sure they're dead though! They probably committed suicide after all their buddies died.

                  Comment


                    Re: Power supply build quality pictorial. part 2

                    Motorola's 2N654x (TO-3-like TO-204) and MJE1300x (TO-220) series parts were their first parts designed for use in switching power supplies, their "Switchmode 1" series. Mot did develop a "Switchmode 2" and a "Switchmode 3" series of parts, but the "Switchmode 1" series were too good, and power MOSFETs came along soon after. I'm glad some MJE1300x parts are still made, and by good companies. A TL494 or 3524 and a couple MJE13007s or MJE13009s can be the heart of a very decent power supply. A "boring" power supply but good power supplies should be boring ... consider the alternative.
                    PeteS in CA

                    Power Supplies should be boring: No loud noises, no bright flashes, and no bad smells.
                    ****************************
                    To kill personal responsibility, initiative or success, punish it by taxing it. To encourage irresponsibility, improvidence, dependence and failure, reward it by subsidizing it.
                    ****************************

                    Comment


                      Re: Power supply build quality pictorial. part 2

                      I am not sure whether I get this post. Are these in this particular PSU?
                      Less jewellery, more gold into electrotech industry! Half of the computer problems is caused by bad contacts

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                        Re: Power supply build quality pictorial. part 2

                        So, on this Max Power (anything but) I was checking the specs of the output rectifiers. I can only identify 2 out of the 3. For the 12V, it has a 10A fast recovery diode (says 18A on the label) and a 16A fast recovery diode for the 3.3V (says 28A on the label). For the 5V, it looks like an actual shottky, but I can't read anything on it. I cleaned it and it looks like nothing was ever printed on it. I was considering taking it cause it's probably a 30A package (label claimed 50A but I doubt it) is it worth desoldering it and seeing if the numbers are possibly on the other side?

                        Edit: Rubbed some water on it with a Qtip and then it showed up but once it dried, it instantly went very very faint again, but anyways, yes it's a 30A shottky.
                        Last edited by Pentium4; 09-04-2012, 02:49 PM.

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                          Re: Power supply build quality pictorial. part 2

                          I got some good experience with silver thermal compound. Once slightly dirtied some memory VGA chips with that and after cleaning it with technical gasoline, the print was much better. Since that time I do it on purpose if I need to read something very faint.
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                            Re: Power supply build quality pictorial. part 2

                            Alright, thanks I guess I should try that some time. Think it's worth taking? I wonder if it even works cause the thing got pretty toasted.

                            Comment


                              Re: Power supply build quality pictorial. part 2

                              Well some of the silver always stays on whatever surface you put it on. And it is better visible on fair surface than on dark so it should improve contrast.
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                                Re: Power supply build quality pictorial. part 2

                                Originally posted by Behemot View Post
                                Well some of the silver always stays on whatever surface you put it on. And it is better visible on fair surface than on dark so it should improve contrast.
                                When I say the thing got toasted, I meant the power supply in general. Not sure about the 5V output rectifier, I'd just have to check it

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                                  Re: Power supply build quality pictorial. part 2

                                  I see…well, not really, from the pictures it does not seem burned more than usual crap of this category. I would expect the board to be brown, or at least orange, but it is fair yellow, no sign of overheat anywhere…?
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                                    Re: Power supply build quality pictorial. part 2

                                    Originally posted by Behemot View Post
                                    I see…well, not really, from the pictures it does not seem burned more than usual crap of this category. I would expect the board to be brown, or at least orange, but it is fair yellow, no sign of overheat anywhere…?
                                    It's definitely really burned, you just can't see very well because I took the pictures with my phone. The only burned parts are around the secondary caps and the little diodes, the secondary output doesn't look burned at all.

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                                      Re: Power supply build quality pictorial. part 2

                                      Isn't it actually some kind of degraded fixing shit, or maybe electrolyte from the bulged cap? First can be mistaken for something burned, second can be aggresive and do whole bunch of things.
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                                        Re: Power supply build quality pictorial. part 2

                                        If you mean the PCB, those cheaper phenolic boards discolour easily with heat
                                        "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
                                        -David VanHorn

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                                          Re: Power supply build quality pictorial. part 2

                                          Originally posted by Agent24 View Post
                                          If you mean the PCB, those cheaper phenolic boards discolour easily with heat
                                          Yeah, that area of the PCB. I also found out later that the fan completely seized up which killed it fast I'm sure cause the efficiency has to be terrible.

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