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Bench supply, Linear or SMPS?

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by Little Ghostman, Apr 20, 2017.

  1. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    I have two really good HP bench supplies I got really cheap at a bankrupt auction. 25V and 5A each. They seem spot on and very accurate, the problem is sometimes you need to erm 'abuse' a PSU. So I tried a ebay special and it was pretty bad, it lasted around 3 weeks and died before I could abuse it properly. I think the HP are linear (not taken them apart), the cheapo one was SMPS. I have a old weller desoldering station that has had it, but the transformer is ok.

    Its 24V but until I find some specs I am not sure of the rating. Is it worth knocking up a bench PSU with it? Or maybe using a SMPS unit with some adjustments? The other question is LT spice, is there a way to do a transformer easily in it? I have started playing with LT spice using some of the demo sims to look at SMPS etc.
     
  2. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Simulators aren't going to help you regarding abusing supplies :D

    It's really best if you don't abuse then - if you find the 'need' then you need something else, not what you're abusing.
     
  3. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    So LT spice dosnt have a smoke symbol, is that what your telling me :D
     
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  4. dave

    Dave New Member

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  5. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    Actually to be more serious, Which would you go for Linear of SMPS. Which can take the odd slip up better, or be designed with reasonable protection in mind? I know this has been done to death on here!! But new regulators etc come out etc, so although I brought a cheapo supply, I am thinking it might be an option to build one. Sometimes i dont want to use something that cost me £25, but is worth alot more, when I am messing with stuff I am not sure wont go wrong!

    I would be gutted if I ruined the HP's but not so much if I ruined one I make. If that makes sense, Also a reasonable bench supply using modern parts might be a good project. Especially if I can flick a switch and have it charge my batteries :D. The HP ones dont like being used as chargers!
     
  6. tomizett

    tomizett Active Member

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    I don't think there's any hard-and-fast rules, really. I suspect (and I'm sure others with more experience will jump in with specific recommendations) that it really is about getting what you pay for to a large extent. If something has been designed to work reliably in a demanding environment then it will - it something has just been designed to sell in volume, then it won't be as reliable.
    I'm sure there are exceptions - as I say, others may have some specific good/bad recommendations.

    I do a lot of my day-to-day tinkering with a simple linear supply I built years ago, which is combined with my soldering iron power supply. That's just got a 7812/7912 in it - about as simple as they come. Despite years of (ab)use, it's never given any trouble. I suspect you want something more comprehensive though - variable output, variable current limit, metering, etc?
    Your Weller transformer, by the way, is probably around the 50VA mark.

    There are tutorials on doing transformers in LTspice but, if you're looking at a linear supply (with a line-frequency transformer) then you shouldn't need to worry about it - a sine voltage source with some series resistance will do fine.
    Looking at SMPS transformers is simple enough in theory, but in my (very limited) experience the difficulty comes in knowing how to actually build the transformer you have designed, or (conversely) knowing (predicting/measuring) what the characteristics of the transformer you have built will be. Dealing with magnetics at this level is outside the scope of most hobbyists (and many pros) and I for one don't have much "feel" for it yet.

    Oh, and regarding "abuse".... it all depends on how you expect to be abusing your supplies?
     
  7. tomizett

    tomizett Active Member

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    And how about repairing the one that died and, while you're at it, trying to see if anything can be improved to stop it happening again?
     
  8. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    The one that died is beyond repair! It has a multimeter like chip inside, this is fried as is the pwm chip. The current limiter must also be gone, because I shorted the supply by accident and it fried itself. Alot of the parts are 3x3mm and no pins, so repairing it isnt worth the effort or cost.

    I like the sound of yours, Yes current limit and voltage settings with a readout and a the obligatory LED, is the kind of thing I had in mind, except I am going through a analogue meter phase, so yes a LCD but voltage and current on a nice analogue meter :D. Mostly because I got a JOB LOT on ebay really cheap:D, all really old from a university clear out.
     
  9. AnalogKid

    AnalogKid Active Member

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    Large HP supplies sometimes are a hybrid of a linear power transformer, then a switching pre-regulator to reduce heat and capacitor size, followed by a tracking linear regulator for low noise and output impedance. The manuals are very often online, complete with schematic and parts list.

    ak
     
  10. JonSea

    JonSea Active Member

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    I'm not really awake and my eyes are blurry this morning, so I apologize if I'm too far off the topic here. If the power supplies still make DC, look at these modules on ebay. You will be amazed.

    These come in a variety of voltage/amperage combinations. I recently got one of the 50 volts, 5 amp versions. Connect a DC source at up to the maximum voltage and any current rating. You then have a spot-on, extremely accurate power supply where you can set the voltage you want, the current you want, power limits. The the menu screen you can set absolute limits, so when you're adjusting any parameter with the rotary encoder, it won't let you exceed those limits.

    The output voltage is what you set within the limits of my Fluke 45 to verify. If you want a constant current supply, set the current with the encoder and what the display says is exactly what you will get when you connect a load.

    These come in up to 15 amp capabilities which use the same module and firmware with an external circuit board. The 2 amp modules seem to include a built-in thermostatically controlled fan; other versions you need to bring your own cooling for higher loads.

    Some of them require use of an external rectifier to charge batteries (which means the voltage readout will be incorrect) While others don't. This feature is spelled out in the specs, so if you want to charge batteries, read carefully.

    There are different firmware versions. I think you'll want one that looks like this. The main display is a large readout of voltage and current, which can be set from that screen with other parameters on a screen with smaller text. Some do not have the large V/A screen.

    Recommended!

    SmartSelectImage_2017-04-20-06-19-06.png
     

    Attached Files:

  11. Cicero

    Cicero Active Member

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    What do you actually mean by abuse?
     
  12. schmitt trigger

    schmitt trigger Active Member

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    Yes it does. Not by default though.
    But you must add it as an .INCLUDE SMOKE spice directive.

    Now seriously...if you want to abuse a power supply (whatever that means), then either you have to build/purchase a bullet proof circuit (expensive), or get a cheap throwaway Ebay module.

    The decision actually boils down to Dollars, Euros or Pounds Sterling.
     
  13. hexreader

    hexreader Member

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    Why not abuse some ATX PSUs?

    They can be found in many skips, or bought cheap new.

    Who cares how many you blow to pieces (just be sure to wear eye protection)

    Maybe invest in a whole load of in-line fuses to limit the potential fire hazards resulting from "abuse"

    I am assuming that Mum has already banished you to the barn so you can't set the main house on fire ;)

    Or the new Scottish pound, which I guess will be called the "Sturgeon" :)
     
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  14. AnalogKid

    AnalogKid Active Member

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    Links?
     
  15. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    I prefer my shed to the house, but I have a room in the house for electronic stuff. Depends how loud the bangs are to how long I get kicked back out to the shed. I like the cheapo ones you got jonsea. I wonder what chips they use. LT has some great ones.
    As for Sturgeon...... I think if my mum could sell up and move back to England she would. Although we have worked really hard to do the holiday thing, but seems to be getting tougher up here at the moment.

    I thought I was going to vote in the next election, but now it will be when I am 21. Choosing a political party is like being asked to choose your method of execution!
     
  16. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    Heard on the news they clamping down on spice in prisons!! apparently its illegal to get caught with it!!! Better be really careful with those sims ;). I had no idea prisons were full of people into electronics!! Apparently they even use drones to get a copy into the prison.
     
  17. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    ATX I already use, but wanted something a bit better.
     
  18. throbscottle

    throbscottle Well-Known Member

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    I designed a somewhat complicated one which has a linear transformer and rectifier/smoother, current pre-limiter to protect the transformer, buck converter and then a linear voltage regulator with adjustable current limit that also makes it work as a constant current supply. It has two channels that can track or be paralleled. All the parts work, I just haven't got it all working together properly yet due to various forms of flakiness in test builds (and I started it 3 years ago!) and stuff I've overlooked (like, how 2.5 + 3 = 5.5, for example). If you want the design PM me, it might work better with a fresh pair of eyes! I was hoping to publish the design on Instructables this month or next, but another hiccup. I don't want to put it on here publicly (there are older versions on ETO though) until I've sorted out the last bits.
     
  19. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    Sounds great!!! Shame you cant publish on here, I understand and respect it though. I might not be much help, but I have enthusiasm and think building a half decent PSU is a kind of right of passage :D. Lets face it, its cheaper to buy them, but everyone has to build at least one! Plus in the last three years new chips and regulators have come out.
    So pm sent :D.
     
  20. tomizett

    tomizett Active Member

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    That's incredibly poor... the very least a bench supply should be able to do is protect itself from a short circuit.

    At work we use the GW Instek GPS3303
    (see http://www.gwinstek.com/en-global/p...y/Multiple_Channel_DC_Power_Supplies/GPS-x303)
    ... it looks like they go under a variety of different badges.
    I can recommend them as being a useful general-purpose supply, and doing what they say on the tin. My only gripe (and it's a significant one, actually) is that you get the entire 0-30V range on one single-turn pot, which makes it very difficult to set precise voltages. How important that is, of course, depends on what you're going to do with it. Looking at RS they're a lot more expensive than I thought they where, so they could be a bit more than you want to pay, although they may well be cheaper elsewhere.

    Kudos to throbscottle for taking the time to make sure his design is watertight before publishing it... from what I hear, not everyone who publishes on Instructibles is so dilligent.
     
  21. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    My HP is excellent, really accurate and precise, but lacks tracking and isnt needed in many cases. Besides there is alot to be learnt from building one, as pointed out it isnt simple if you want some decent functions on it. But aa great experience if you pull off a half decent job!

    The cheapo one has a place on the board for a fuse and fuse holder, it looks like there is just a jumper wire there! It was a cheapo and while I thought it was worth the money, I was surprised it died without any real attempt to kill it :D. Ironically the HP ones are said to be almost bullet proof! But it nags at me that it would be a long long time before i could replace one :D.

    The desoldering station by the way is heavy, it has a desoldering iron and can run another soldering iron at the same time, it also runs the suction pump. No idea what size it is yet, but should be a bit bigger than the normal old weller solder stations. The pump has gone on it, and some other bits are missing, I have another weller desoldering station I got at the same time, that one works a treat and was super cheap. I wouldnt be without one now!
     

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