Hot!High Voltage Power Supply

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Ioannis
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2018/02/01 01:55:16 (permalink)
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High Voltage Power Supply

Looking for help on High Voltage Power Supply.
 
Requirements are:
Output 10-300 Volt/400mA
Adjustable voltage and current (CV/CC)
Display status on a LCD by means of a MCU that will control the P.S. as well.
Power from 240Vac line.
Initially started on a linear power supply but power losses are too much and I reject this idea. So turned to SMPS design but could not find proper parts for the above range of control.
 
Any help, ideas appreciated.
Ioannis
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70 Replies Related Threads

    DavidBLit
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    Re: High Voltage Power Supply 2018/02/01 10:25:16 (permalink)
    +2 (2)
    You might try posting to a forum that is at least remotely related.  Hint: this ain't it.

    Yeah, "//Code and stuff".
    #2
    Bob White
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    Re: High Voltage Power Supply 2018/02/01 12:02:18 (permalink)
    +1 (1)
    What you are attempting is not a simple task.
     
    My usual warning: if you are not experienced in designing mains connected equipment, and switch mode power supplies in particular, STOP!  Working with mains connected electronics is dangerous - both for you and the eventual user of your product.  There is a real possibility of causing a fire, simply getting hurt, or even getting killed if you do not know and follow good safety practice and procedure.  Find somebody local that is experienced and can guide you through the design, construction, and testing of such a power supply.
     
    All that said, a basic question is are you attempting this as a home project or experiment, as a school project, or as a design for a product that you want to sell?

    And as above, there are better forums (such as any number of power supply design groups on LinkedIn) for this question.
     
    #3
    Ioannis
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    Re: High Voltage Power Supply 2018/02/01 14:19:54 (permalink)
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    Thank you for the replies.
    This is not a home project or experiment. I know the risks, (as I am an electronics engineer for 35 years but not specifically on power SMPS).
     
    I was suggested to explore the Phase shifted technique. Looks interesting.
     
    Regarding the relation to MCU, I think it is directly related as it will be controlled and monitored by an 8-bit PIC with LCD and Keyboard.
     
    An PWM enabled PIC is a must to control either H bridge or a Linear circuit.
     
    In any case I will not bother more and an Administrator/Moderator can freely delete this thread if not related to the rest of the forum.
     
    Ioannis
    #4
    jack@kksound
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    Re: High Voltage Power Supply 2018/02/01 14:41:40 (permalink)
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    I think you will get more (eager) help when you ask more specific questions that deal with the pic and programming. There are a few who frequent this forum that have a great deal of knowledge in the power supply arena and quite a few with same in pic programming and hardware design. Stick with it and ask more specific pic related questions.
    #5
    qɥb
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    Re: High Voltage Power Supply 2018/02/01 14:58:40 (permalink)
    +1 (1)
    +1
    particularly when you are asking about a device that can easily kill people!
     

    This forum is mis-configured so it only works correctly if you access it via https protocol.
    The Microchip website links to it using http protocol. Will they ever catch on?
    PicForum "it just works"
    #6
    PStechPaul
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    Re: High Voltage Power Supply 2018/02/02 00:38:11 (permalink)
    +2 (2)
    I would advise starting with a 0-12V or 0-24V switching supply and then simply scale up to 300 volts when you have the low voltage design working. Here is a pretty good app note for SMPS topology selection:
     
    http://ww1.microchip.com/downloads/en/AppNotes/01114A.pdf
     
    Here is a project to make a 0-45 VDC at 8 amp switching supply. It doesn't use a PIC but you could adapt it to use a microcontroller:
     
    https://www.eleccircuit.com/0-45v-8a-dc-switching-power-supply-circuit/
     
    Here is a 3-60 volt, 40 amp, switching power supply project:
     
    http://www.danyk.cz/reg60v_en.html
     
    Here is a simulation of a simple PWM DC supply:
     


     
    #7
    Peter Sikora
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    Re: High Voltage Power Supply 2018/02/02 02:14:19 (permalink)
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    I was suggested to explore the Phase shifted technique. Looks interesting.

    I don't think you are going to get that out of an 8 bit PIC. more like fast dsPIC maybe. Having 25years of PSU experience with Battery charger and inverter technology. While your output power requirements are not great ~150W
    I think your request is out of the realm of this forum of mostly software related engineers. (I welcome contributors comments on this if they feel I am being unjustified) Try looking at AN1421 - Platinum-Rated AC/DC Reference Design Using the dsPIC DSC for a start.
    #8
    PStechPaul
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    Re: High Voltage Power Supply 2018/02/02 04:01:54 (permalink)
    +2 (2)
    Quite some time ago I designed a DC power supply with outputs of 48, 125, and 250 VDC, at 1 amp, using a phase-fired SCR. The disadvantages are that you need a 50/60 Hz transformer for isolation, and you need large, heavy inductors and capacitors on the output for filtering. Output regulation is also tricky, especially with light loads. High frequency switching supplies have many advantages of cost, size, and weight.
     
    I found a pretty comprehensive resource for various types of power supplies, including phase-fired SCRs or TRIACs:
    http://www.delftek.com/wp-content/uploads/2012/04/HP-power-supply-handbook.pdf
     
    Some SCR theory and circuits:
    http://www.nutsvolts.com/magazine/article/scr_principles_and_circuits
     
    More SCR info:
    http://www.mcgoff-bethune.com/manufact/cci/technical/SCR-Guide.PDF
     
     

     
    #9
    Ioannis
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    Re: High Voltage Power Supply 2018/02/02 13:54:55 (permalink)
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    Thank you all for the replies.
     
    MCU will be used for the monitoring of the operation, so 8-bit hopefully is OK.
     
    Ioannis
     
    P.S. I can only post on the same PC that I opened the thread. Is this normal?
    post edited by Ioannis - 2018/02/02 13:56:09
    #10
    Peter Sikora
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    Re: High Voltage Power Supply 2018/02/03 01:49:07 (permalink)
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    So how were you thinking of using phase shifting? I upvoted @PStechPaul for providing you with design information to research, but with today's PFC requirements and EMC compliance I don't think SCR switching is going to cut it. Certainly not if you are looking to regulate from 10 to 300V with a good clean DC output. Like @PStechPaul says you will need big inductors and filter capacitors. Hardly seems worth it for 400mA output with marginal performance.
    post edited by Peter Sikora - 2018/02/03 02:39:47
    #11
    Bob White
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    Re: High Voltage Power Supply 2018/02/03 15:06:47 (permalink)
    +3 (3)
    Some questions about what you are trying to achieve...
     
    Is this a development of a product to be sold?  If so, what markets (geography and application, so that we can know what safety and EMI regulations apply)?  For example, if this is a laboratory instrument then the safety requirements are much different than for medical equipment.
     
    What are the development priorities (and all of these cannot be the priority)? BOM cost, sales price, development time, size and weight, efficiency.
     
    You say 240 Vac input.  What is the actual input voltage over which the unit must work properly?  Do you have operate with sustained 275 Vac such as in China or parts of Australia?  Do you have to work at 200 Vac as in Japan?  This goes back to the markets question but also the application.  What range of input mains frequency?  47 -53 Hz? 45 - 55 Hz?  45 - 65 Hz?  What are your requirements for the ride through of ac power sags and dropouts?
     
    Does the dc output need galvanic isolated from the ac input?  If so, presumably with reinforced insulation.
     
    Does the input require power factor correction?
     
    What is the communications interface between the user and the power supply control and monitoring circuit?  Are you going to use an established protocol such as the PMBus®?  Use your own protocol over a RS-232 line?  Put an embedded web server in the power supply and communicate via ethernet or a wireless link?  USB with a custom driver?
     
    I know this is a lot of questions but it only the start of what one needs to know to do this project.
     
     
     
    #12
    Ioannis
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    Re: High Voltage Power Supply 2018/02/04 12:17:36 (permalink)
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    Peter:
    There is a pdf by TI http://www.ti.com/lit/ug/tidu248/tidu248.pdf that shows a step down regulator using phase shifting.

    Using a PWM to regulate say, 300V with 80% duty cycle, down to 10volts would need 2.67%, or in terms of pulses too narrow to obtain with a PWM control.

    Based on the above pdf I am trying to figure how this can be modified for my needs.

    Bob:
    Well, the design is about an Electrophoresis power supply to be sold in EU market (230-240Vac/50Hz). The main power is no problem.

    Galvanic isolation is needed and at least I can use double transformers for this.

    PFC is not a priority right now.

    Communication with the rest of the world not needed. Only internal MCU (settings and display).

    All the above is not a problem. My concern is on the wide range that the supply must work (10-300V dc/0-400mA) as a constant voltage/constant current supply.

    EEVblog had a tear-down of such a supply with a very limited schematic, but seems it is working like an IGBT switch charges the output capacitor in this link https://www.youtube.com/w...ue=1&v=1j4L4ecjUz0

    Ioannis
    #13
    PStechPaul
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    Re: High Voltage Power Supply 2018/02/04 14:51:16 (permalink)
    +1 (1)
    I don't see the difference between the TI phase shifted supply and an ordinary PWM supply, like this:
     

     
    My understanding was that a phase shifted design worked on the AC side. The TI design assumes a DC bus which would be produced by rectifiers and capacitors on the AC line, like an ordinary switching PSU. PFC would be much desired, especially for higher power applications.

     
    #14
    Peter Sikora
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    Re: High Voltage Power Supply 2018/02/04 15:23:17 (permalink)
    +1 (1)
    As @BobWhite pointed out about the your input voltage range problems you can overcome this by using a Power Factor Correction circuit with wide input voltage range of 85 - 265V. This will give you a non isolated DC voltage of 385V. Have a look for International Rectifier AN-1077 which uses the IR1150S. You could then chop and feed that power in through an isolated transformer to get your 10-300V. For 8 bit PWM, 300V / 255 steps gives you a resolution of 1.1765V per step. If you need better resolution there are a few more options. I think your TI phase shifted control solution is tending towards a dsPIC device rather than a simple 8 bit device. You have some choices.
    #15
    Ioannis
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    Re: High Voltage Power Supply 2018/02/05 02:13:34 (permalink)
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    The not so strict specs of my client, require 1 volt step. The mid PICs have also 10-bit PWM which would cover it just fine I suppose.
     
    IR1150S look good for the PFC. My concern is on the 385V Bus chopping down to 10. PWM Pulses have to vary from 80% down to 2,7% and that drives me to think Phase shifting as an alternative.
     
    Also, I forgot to mention, speed is not critical in such applications. Meaning that user sets the output voltage and then hits the button to activate the output.
    #16
    PStechPaul
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    Re: High Voltage Power Supply 2018/02/05 02:49:03 (permalink)
    +1 (1)
    I found several suppliers of electrophoresis power supplies, to see what sort of specifications they might have. Here is one:
    http://www.bio-rad.com/en-us/product/powerpac-universal-power-supply?pcp_loc=catprod
     

    Mostly, I wanted to know such things as ripple, step response, overshoot, and overcurrent protection. The model shown above has modes for constant voltage, constant current, and constant power. Also programmable with storage capacity, and other features. It's about $2500.

     
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    Peter Sikora
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    Re: High Voltage Power Supply 2018/02/05 04:42:50 (permalink)
    +1 (1)
    PWM Pulses have to vary from 80% down to 2,7% and that drives me to think Phase shifting as an alternative.

    The beauty of pulse width modulating a regulated and steady voltage is that if your on time is say 10% of the total time you can expect 10% of the voltage to be present on the output. It then simply becomes a problem of proportionality. If you are guaranteed the the per-regulator is giving you 385V then at 10 bit resolution (1024 steps) each step will guarantee to give you 0.376V per step. Of course if your PWM frequency is too high you may have inductance to consider, and if too low, switching noise will be difficult to filter out. Much easier to go for standard PWM technique with a H'bridge where you can program some dead time into your switching. This will help prevent FET's or IGBT'S from blowing up due to cross conduction. PWM and 8bit CPU will work fine for that. I implemented a similar thing for a micro step stepper motor drive and it worked as advertised.
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    Ioannis
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    Re: High Voltage Power Supply 2018/02/05 05:25:34 (permalink)
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    For the purpose of electrophoresis, ripple, noise or perfect regulation, fortunately, is not too important. The load is almost stable, so the voltage, given the source is pre-regulated, will be stable too.
    Now, for a PWM freq of 1KHz, the 385Volt at 80% duty gives about 308 Volt and pulse width of 800usec.
    At 2,7% gives 10,4 Volts and a pulse width of 27usec.
    My selection of 1KHz is more of a random to the lower side, so that the pulse width is not too narrow.
    I think it is viable to control a pass MOSFET from a 385V dc rail to a 10-300 volt at the output.
    #19
    Peter Sikora
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    Re: High Voltage Power Supply 2018/02/05 05:55:16 (permalink)
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    1KHz is too low and would be audible and output transformer would be larger. Anything 20KHz and above would be more suitable (25KHz - 40KHz). Most conventional PWM converter IC's easily operate at these frequencies. Don't forget that PFC pre-regulator is not isolated so you need to drive a second transformer to provide isolation. I can see from EEVblog video that output regulation is poor by PSU standards and this is acceptable. I think I was able to operate a PIC16F73 at 20Khz PWM output frequency. It's just out of the audio range. There are much more choices of CPU now.
    #20
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