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DC/DC converter with propeller — Parallax Forums

DC/DC converter with propeller

max72max72 Posts: 1,155
edited 2009-06-17 05:20 in Propeller 1
I would like to investigate the possibility to use DC/DC converters in place of linear regulators.
I'm working on a battery powered project, including GPS, 2 or 3 LCDs and a couple of other components.
At the moment I use a 12V gel battery with a protoboard, stretching the capability of the board itself. To improve the setup I would like to switch to a couple of DC/DC converters in order to provide the +5V and the +3.3V.
As far as I know there is a ripple left and I am concerned it could cause problems to the components.

Any suggestion is appreciated.

Regards,
Massimo

Comments

  • Peter JakackiPeter Jakacki Posts: 10,193
    edited 2009-06-16 12:31
    There have been quite a number of schemes discussed before. Myself, I use the LM2594 in the 8-pin SOIC pack. This provides the bulk 5V output from which I may have one or more 3.3V linear regulators such as the LM2985 in the SOT-23 pack. I rarely would use any of the bulky packages such as the SOT-223 or the TO-220 as these are totally unnecessary.

    As to ripple, well the 3.3V linear regulator is fed from the 5V supply so it is nice and smooth but the ripple on the 5V is absolutely minimal anyway as the switchers operate at 100Khz or more. If you really want to it is easy to add a small post-filter to remove that last bit of high-frequency ripple but usually I don't have anything on the 5V rail that is fussy about it anyway.

    *Peter*
  • RaymanRayman Posts: 14,838
    edited 2009-06-16 12:33
    The biggest problem you have is going from 12V to 5V... I would recommend something like the LM2596 with S34566 coil and 1N5822 diode for that. Add a 100uF cap on the input and 330uF cap on the output. The ripple is small.

    There's not much loss going from 5V to 3.3V if the current is low, so I'd just use a regular regulator there...

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    My Prop Info&Apps: ·http://www.rayslogic.com/propeller/propeller.htm
  • mctriviamctrivia Posts: 3,772
    edited 2009-06-16 14:50
    Efficiency would not be to bad with 3.3 linear and switching 5

    I use a 63001 to get 3.3 on my propmod-us_ps

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    propmod_us and propmod_1x1 are now in stock. Only $30. PCB available for $5

    Need to upload large images or movies for use in the forum. you can do so at uploader.propmodule.com for free.
  • max72max72 Posts: 1,155
    edited 2009-06-16 19:29
    It looks 5v switching and linear 3.3 is the way to go..

    Thanks!

    Massimo
  • mctriviamctrivia Posts: 3,772
    edited 2009-06-16 19:33
    Yes if you do not need the best possible and not drawing to much on 3.3 side. I use switching so I can have input voltage from 1.8-5.5 v

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    propmod_us and propmod_1x1 are now in stock. Only $30. PCB available for $5

    Need to upload large images or movies for use in the forum. you can do so at uploader.propmodule.com for free.
  • Timothy D. SwieterTimothy D. Swieter Posts: 1,613
    edited 2009-06-16 23:59
    I also use the LM2594. In fact I have a prototype sitting here that I hope to power up later this week with the LM2594 setup as a 3.3V supply (I only needed 3.3V).

    Here is a list of parts used to put together the power system (kind of ugly list, I pasted it from Excel):
    1 LM2594 Switching regulator, 3.3V output, 500mA SMD: 8-SOIC National Semiconductor LM2594M-3.3/NOPB Digi-Key LM2594M-3.3-ND
    2 47uF Capacitor, tantalum SMD: 7343-31 10%, 16V AVX Corporation TAJD476K016RNJ Digi-Key 478-1739-1-ND
    1 100uH inductor SMD 20% Murata 46104C Digi-Key 811-1170-1-ND
    2 MBRS130 Schottky diode SMD: SMB 30V, 1A ON Semiconductor MBRS130LT3G Digi-Key MBRS130LT3GOSCT-ND
    1 Yellow LED Yellow LED, face up illumination, clear, 140 degree viewing SMD: 0805 CML Innovative Technologies CMD17-21VYC/TR8 Digi-Key L62407CT-ND
    1 120 Ω Resistor SMD: 0805 1%, 1/4W Vishay CRCW0805120RFKEA Digi-Key 541-120CCT-ND

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    Timothy D. Swieter, E.I.
    www.brilldea.com - Prop Blade, LED Painter, RGB LEDs, 3.0" LCD Composite video display, eProto for SunSPOT
    www.tdswieter.com
  • Fred HawkinsFred Hawkins Posts: 997
    edited 2009-06-17 02:58
    TI has just promoted a new chip. From their email:

    TI's TPS54620 is the industry's smallest single-chip, 6-A
    ·step-down switcher with integrated FETs. The 95-percent
    ·efficient device is 60 percent smaller than today's multi-chip
    ·converters, and results in a complete 6-A power solution less
    ·than 195 mm² — one-fourth the size of a postage stamp. The
    ·1.6-MHz monolithic DC/DC converter supports input
    ·voltages from 4.5 V to 17 V, allowing it to manage
    ·space-constrained 5-V and 12-V point-of-load designs.
    ·Features·

    ····· 14-pin, 3.5 x 3.5-mm QFN package
    ····· 200-kHz to 1.6-MHz operation,
    ····· synchronizes to external clock
    ····· High-efficiency 26-/19-m? Rds(on)
    ····· integrated MOSFETs
    ····· ± 1% voltage reference accuracy over
    ····· temperature
    ····· Power-good, enable and tracking pins for
    ····· sequencing
    ····· Easy-to-use, downloadable,
    ····· SwitcherPro™ design tool

    ·Applications·

    ····· Broadband, networking and
    ····· communication infrastructure
    ····· Servers and work stations
    ····· Compact PCI / PCI Express / PXI
    ····· Express applications
  • Ole Man EarlOle Man Earl Posts: 262
    edited 2009-06-17 04:17
    Looks good. TI's sample site is down. Digikey has them for $4.83 in single lots
  • Timothy D. SwieterTimothy D. Swieter Posts: 1,613
    edited 2009-06-17 05:20
    I saw this e-mail from TI as well. The price isn't too bad, I am just not sure why I would need up to 6 amps, but I see they have versions with lower current maximums. The QFN package though is a little harder for hobbyists to hand solder. It looks like a good choice for a project with motors or servos in it as well as electronics.

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    Timothy D. Swieter, E.I.
    www.brilldea.com - Prop Blade, LED Painter, RGB LEDs, 3.0" LCD Composite video display, eProto for SunSPOT
    www.tdswieter.com
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