Boost Converter

Discussion in 'General Electronics Chat' started by R!f@@, May 28, 2015.

  1. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
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    Looking for diagram any one made.
    Basically I need to boost a 3.7V Li-on to 30VDC. Max 100mA.

    Any one ?
     
  2. pwdixon

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    Oct 11, 2012
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    Lots of LM2577 based modules available on the internet, they all look pretty much the same and I would guess they come straight out of the datasheet.
     
  3. R!f@@

    Thread Starter AAC Fanatic!

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    Ya, I have seen that.
    Looking for a quick DIY.
    It will take a month for those to reach me.
     
  4. MrAl

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    Jun 17, 2014
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    Hi,

    What parts can you use then?
     
  5. R!f@@

    Thread Starter AAC Fanatic!

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    I have quite a lot.
    Need to know or see the schema u know
     
  6. AnalogKid

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    Aug 1, 2013
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    Linear Tech's LT1070 or 1071, 1270, 1370, etc. I use their circuits straight off the data sheet. For 0.1 A output current, you need a minimum 1A switch. LTC has a long app note that is an excellent design manual for all kinds of simple switching converters. For a smaller package consider their 1377.

    Vishay LPE-5047 is a nice off-the-shelf multi-winding inductor that can be configured as a flyback transformer or boost inductor.

    ak
     
  7. pwdixon

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    Oct 11, 2012
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    You must know if you have a booster chip surely? I assume therefore that what you really want is a schematic based on non-single chip solutions eg using something like a 555/op-amps or transistors.
     
  8. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
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    I have set down DC to DC that is sold from china. These works well as a buck.
    I believe it uses the LM2596S chips.
    Wondering if it could be used to boost the voltage.

    I have seen the 555 booster. A little bigger than I expected.
     
  9. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
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    Crap.! LM2596 cannot be used as a booster.

    I have seen an LT chips from my junk somewhere. I guess I need to start digging.
     
  10. ian field

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    Oct 27, 2012
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    You could probably do it with a "Joule thief" style blocking oscillator, normally they operate from a 1.2 - 1.5V cell, the higher voltage means you need a slightly different feedback/bias arrangement. The feedback path needs a DC blocking capacitor, so then you'll need a base bias resistor to get the transistor started.
     
  11. DickCappels

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    Aug 21, 2008
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  12. ronv

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    Nov 12, 2008
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    It sounds easy, but it is not as easy as it sounds. :D
    100 ma is quite a bit for the little joule thief type circuits.
    Is the load a constant 100 ma or is it more like 0 to 100 ma.
    How about tolerances 10% ok?
    Is switching ripple or noise an issue?
    I have crude one based on a 555, but for the low voltage (3.7 volts) it would need a powered up cmos 555 to work.
    Anyway, do you have any logic level FETs or fast low saturation NPNs good for 3 amps or so?
    Also needs a 470 uh 2 amp or larger inductor. Everything else is pretty vanilla.
     
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  13. R!f@@

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    I believe my load is stable as they are just LEDs.
    I think I can find logic level FETs.
    I might need to wind an inductor. I have an inductance meter.
     
  14. RichardO

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    May 4, 2013
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    Just remember that any inductor make must not saturate. Saturation current is a pain to measure since you have to measure the inductance with a large direct current flowing through the inductor.
     
  15. ian field

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    Oct 27, 2012
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    The basic self oscillating flyback converter that resembles the basic layout of the "Joule-thief" was a popular choice for the PSU in 80s home computers, Atari and Amiga are two such units I had a contract to repair PSU boards for.

    The DC input is about 320V, so using a center tapped primary and feeding the other end back to the base via a resistor wouldn't work so well. The feedback part of the winding is isolated from the main primary and fed to the base via a DC blocking capacitor.
    The voltage developed by the feedback winding is also rectified and smoothed to supply the opto-coupler transistor in the regulation loop. Regulation is effected very simply by a medium power transistor that shunts the B/E of the chopper transistor - a current sensing emitter resistor also feeds back a voltage to the base of the clamp transistor to limit overcurrent.

    Atari & Amiga are yust 2 makes I can remember - there were oodles of small board open frame switchers that used a circuit based on the "Joule-thief" style.
     
  16. ronv

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    Give this a look. Normally it's not good to run a bosst converter in discontinuous mode but in this case the load is stable so I think it is ok. It needs a high current inductor, but maybe not to bad.
    You can adjust voltage or use constant current for your leds. Q1 for voltage adjust or Q2 and the resistor for constant current. If you use both make sure the voltage is set higher than needed to supply the current desired.
     
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