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Dual Output Lab Supply: 0 - 16V/3A

Discussion in 'Electronic Projects' started by bountyhunter, Aug 7, 2009.

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  1. bountyhunter

    bountyhunter Well-Known Member

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    Dual Output Lab Supply: 0 - 16V/2.5A

    I am posting the schematic for a dual output lab supply I designed some years back and built for my own lab bench. It's a good learning project and can be simplified or built fully depending on complexity level of the builder. I am going to try to post the PDF file, then I will add technical info if it does go through.... to save a half hour of typing only to find out it won't post.
     

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    Last edited: Aug 7, 2009
  2. bountyhunter

    bountyhunter Well-Known Member

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    The power supply uses dual outputs which are basically the same except for some connections to do specific things like auto parallel or stacking outputs.

    The outputs are fully floating and can be stacked up or down. They can also be paralleled because of the auto parallel circuitry.

    The unregulated supplies put out about 18V DC on each side. The voltage regulator is done by the 2N5885/2N6124 current drivers controlled by the voltage error amp That amp uses a 2.49V LM336 voltage reference. The VADJ pots allow you to adjust the voltage from zero to 16V. LM358 op amps are used throughout so no negative supply is needed (saves space it's a small chassis it had to fit into).

    The voltage amp runs the PS in constant voltage mode unless or until the load current is high enough to reach the value set to the current error amplifier, which also uses a 2.49V reference and pot adjustment to set the current from zero to about 2.7A. Note the current error amp has top priority, because it can take the drive from the output of the voltage error amp. Thus, it forces the voltage down if the current reaches the set value.

    The design incorporates thermal shutdown with a transistor glued to the heatsink between the power transistors. U2B shuts the power supply down if the temp gets too high by programming both sides to zero output current. The B side is run through an opto isolator to allow the outputs to be stacked.

    The auto parallel mode is used by strapping both negative output terminals together first, then adjusting the B side voltage and current pots to maximum. The A side current is used to provide the reference voltage to the B side current error amp, so it tracks the A side (current shares). By adjusting the B side I ADJ pot, you can have the B side current track the A side in any ratio up to 100% of A side.

    There are "CUR LIMIT LED" indicators which show when the current error amplifier has taken control, meaning the PS is in constant current mode. If these are not lit, it is in constant voltage (CV) mode.

    There is also an LED to show when auto parallel is engaged.

    The total design can be simplified by eliminating auto parallel and thermal shutdown. Any good 2.5V reference can be used such as LM385 or similar.
     
    Last edited: Aug 7, 2009
  3. tytower

    tytower Banned

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    About 10 years ago Silicon chip magazine published a 40 V 3 A project and a 45V 8A model. I built the smaller one at the time and still use it.

    It has all the features of overheating shutdown and current and voltage limiting so why is yours different or special ? Why have you posted this when the SC model is available as a kit ready to assemble?
    Why would I use yours is what I am asking you ?
     
  4. dave

    Dave New Member

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  5. picbits

    picbits Well-Known Member

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    Because this forum is a community and we share our designs and ideas ?

    It could be that another member hasn't got access to the Silicon Chip project ?

    Maybe people want to make their own projects from scratch and not buy a kit from Silicon Chip ?
     
  6. bountyhunter

    bountyhunter Well-Known Member

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    The auto parallel feature is extremely useful, it doubles the output current capability for the unit. You can strap the outputs in parallel and they share current equally (and don't fight for control).

    As to why I posted it: as a general information tool to show how linear regulators work. For example: there is a parallel thread running about a dual rail power supply in a freq synthesizer with a blown power supply and the person trying to fix it didn't know how it works. The basic building blocks of this unit show how the insides of virtually every linear regulator work including that unit's power supply.

    As for what's available as kits: I have no idea. But, there are a lot of people with parts laying around they could turn into projects. That is actually when you know you have learned to be a designer: you have a need for something, you have a pile of parts and an old chassis, and in your mind you see how they can come together to make something useful. In order to do that, you must first have an understanding of circuit building blocks. Kits are useful, but building from scratch is about 1000X as informative.
     
    Last edited: Aug 8, 2009
  7. bountyhunter

    bountyhunter Well-Known Member

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    Or maybe they need an output voltage or current that isn't covered by that particular design and would build their own if they knew how?
     
  8. tytower

    tytower Banned

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    Fair enough - I'll have to study that auto parallel feature.
     
  9. qbone

    qbone New Member

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    Hello Bountyhunter, thank you very much for posting this PSU, this project looks very attractive.
    Do you by any chance have the PCB for it?
    Also, would a 2x15V/120VA transformer be sufficient to run this?

    EDIT: removed question regarding wattage requirements for resistors, I didn't look at the schematic carefully enough :)
     
    Last edited: Sep 2, 2009
  10. bountyhunter

    bountyhunter Well-Known Member

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    No, sorry. I built it on regular blue vector board with point to point wiring.

    Does that mean the transformer has two separate outputs and each one is rated at 15VAC @ 4A? If so, that should work.
     
    Last edited: Sep 3, 2009
  11. Airian_007

    Airian_007 Member

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    Help Need For Project

    Hi
    I need your help in my project in wich i have to make a regulated and adjustable power supply (0-30)V but it seems to be easy but the main thing is that i want to add a led bar in my project so that when the voltage range is in b/w (0-10)v then only 2 or three led's (green) depending on the bar should be lighten and as we increase the voltage to 20 then amber led's along with green should be lighten and simmilarly red along with green and amber should glow as we reach to 21v-30v
    so plzz help me and give me some suggesions on how to do this?
     
    Last edited: Nov 10, 2009
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