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Design Challenge 3: Power Supply Circuit/Regulator Needs

Editor’s note: Here is a third Design Challenge from one of our readers. Please feel free to make suggestions and comments/questions, and the author will respond. Maybe we can even improve upon the design.

Opportunity for improving this design: We have an analog power supply circuit for one of our products that employs an obsolete LAS6350 regulator, and we need to update this. The circuit was originally designed to accept either an AC or DC input, but we now use only 24V DC.

We would appreciate your recommendation on our best design configuration and regulator for replacement. Our Vin is 24V DC with Vo at 2.55V DC. Current is less than 1A.

Below is a schematic and data sheet of the old Lambda regulator:

Power supply schematic with LAS6350

Power supply schematic with LAS6350

Sheet 1 of LAS6350 data sheet

Sheet 1 of LAS6350 data sheet

Sheet 2 of LAS6350 data sheet

Sheet 2 of LAS6350 data sheet

Sheet 3 of LAS6350 data sheet

Sheet 3 of LAS6350 data sheet

Sheet 4 of LAS6350 data sheet

Sheet 4 of LAS6350 data sheet

Sheet 5 of LAS6350 data sheet

Sheet 5 of LAS6350 data sheet

Our circuits for this system are all analog, which I would like to maintain as I feel we obtain the best precision of measurement as well as durability in harsh environments

Your suggestions and recommendations will be greatly appreciated.

20 comments on “Design Challenge 3: Power Supply Circuit/Regulator Needs

  1. antedeluvian
    May 26, 2014

    Our circuits for this system are all analog, which I would like to maintain as I feel we obtain the best precision of measurement as well as durability in harsh environments

    I am not sure what we are being asked here. Does the reader want a pin replacement part? Is he going to re-lay out the PCB? Will a SMT part work? And I am not sure how to parse the above statment. Is he looking to redesign the whole analog circuitry? Or is he saying that he is worried that the noise from a SMPS will be a problem.

    At any rate, let me suggest the TI Simple Switcher LMZ14201 or its brothers which is a single chip solution (although he will need a few caps and resistors) to his power supply conundrum, provided he is prepared to go with a new PCB. It has everything including the magnetics built in. Of course it works at a much higher frequency and the noise/ripple is going to be different to his current design. I hope it doesn't affect it adversely. Of course he can follow the advice given here on Planet Analog to follow the SMPS with a linear regulator.

     

     

     

     

  2. eksb
    May 27, 2014

    Thanks for your response. We are redesigning the PCB to accommodate the replacement regulator and some other changes. If a SMT will provide maximum precision and reliability we will certainly adapt that into our circuitry.The possibility of noise is a concern. Off-hand the LMZ14201 looks promising. What capacitors do you recommend we use with this?

    Thanks much.

     

  3. samicksha
    May 27, 2014

    I guess re-lay for PCB is not required, we already have simple PCB layout with mounting capability.

  4. antedeluvian
    May 27, 2014

    eksb

    What capacitors do you recommend we use with this?

    I have only used the device in one design. I used the values on the data sheet using ceramic and low ESR tantalum. The data sheet covers the selection.

     

    FWIW Wurth sells a similar (identical?) part, even using the same number. My guess is that it is made in the same factory.

     

  5. eksb
    May 27, 2014

    Thanks very much for your help. We'll try this.

  6. antedeluvian
    May 27, 2014

    eksb

    At the risk of muddying the waters, some time back TI also took over a company called Power Trends who produced similar regulators that were ahead of their time. They had some through hole products- you may want to look here. At the time (~1995 IIRC)  their price rose dramatically when TI took them over. I don;t know the relative pricing today.

  7. eksb
    May 27, 2014

    You have a good memory. These look like they might work as well and the price is reasonable for our needs. Thanks again.

  8. RedDerek
    May 28, 2014

    @eksb – if you are indeed making a new PCB layout, then you have many options before  you as suggested. If trying to do a drop-in, the challenges go up several notches.

    I currently work for a company that has the later issue to deal with – I constantly have projects where I essentially have to replace a black-box with another within the same form, fit and function.

  9. wawaus1
    May 28, 2014

    At the risk of confusing your choice, I have been using the Linear LT8610 very successfully in a similar design. You could also consider the LT8611 or LT8620.

    Best regards

    Bill

  10. DynaMho
    May 28, 2014

    SMPS is not the only way depending on the load, so the first question is “what is the load”?

    If the load is fixed, a NON-SMPS solution would be the best.

    I have found that a purpose built design based on the load can save on the BOM.

    I love counter EMF, but just not in my designs if it can be avoided.

  11. Netcrawl
    May 29, 2014

    @antedeluvian you're right TI, the growing complexity of power management creates real challenges, plug-in power supplies are a growing trend in power management and TI expect demand for plug-in power supplies to grow within five years. I guess this is the reason why TI acquired Power Trends, Power Trends is a leading supplier of fast-growing market for power solutions.  

  12. Netcrawl
    May 29, 2014

    @wawaus1 Linear LT8610 is great, its a compact, high-efficiency switching regulator that consumes only 2.5 uA of quiescient current, its proven and guaranteed to meet today's challenges, and I have no problem using it.

  13. chirshadblog
    May 30, 2014

    @Netcrawl: Yes it's always good to take a few risks especially with technology since only if you take risks you will know that it's a risk or not. 

  14. chirshadblog
    May 30, 2014

    @netcrawl: Thank you for the update. Im planning to use it during the weekend for a short term project. Will update on the status of the device soon. 

  15. chirshadblog
    May 30, 2014

    @ekab: Yes the price is reasonable for the mentioned features but you do have to use it for some time and see the compatibility and the reliability of it. Then only we can figure out the value of it

  16. eksb
    May 30, 2014

    One of the nice thngs about EDN is the help that everyone is willing to provide. Thanks to all who responded to my request and especially to Steve for initiating this blog. I appreciate it greatly.

  17. geek
    May 30, 2014

    @eksb: I agree with you. It was indeed quite a helpful blog and answered a great deal of questions. I think that's one of the things I like about this community – it's quite a helpful bunch of people who also happen to be very knowledgeable in their areas.

  18. Netcrawl
    June 1, 2014

    @eksb EDN provide a huge database of useful information about power supply and regulator, learning tools, enguineering resources and etc. everything you need.

  19. eksb
    June 1, 2014

    Thanks. I've begun digging into some of them. Great stuff and very helpful.

  20. eksb
    June 1, 2014

    Thanks. I've begun digging into some of them. Great stuff and very helpful.

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