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Adjustable Linear Regulators (reguladores de tensão)

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  • 8/12/2019 Adjustable Linear Regulators (reguladores de tenso)


    Adjustable Linear Regulators

    The Other Voltagespage showed how a fixed voltage regulator like the LM7805 could be rigged to

    give a variable output, ad this is !ust what "al#a do i their little $a#ate %% cotroller&This

    regulator sets the #ii#u# output at 5V, #axi#u# is about '&5V below the igoig suppl( level&

    Maxi#u# load will deped o the si)e of heatsik fitted up to the chip*s '+ li#it& The $a#ate

    ol( has a s#all sik, li#itig loads to 0&5+ -./ so (ou #a( wat to build a #ore powerful

    versio ador #ake oe #ore suited to pael #outig&

    The circuit is straight fro# the Texas %stru#ets datasheetad %*ve icluded the reco##eded

    s#all capacitors 1 these should be fitted ear to the regulator iput ad output pis to prevet itfro# oscillatig uder so#e circu#staces& The "al#a circuit does*t bother with the#, but it ol(

    saves a few pece&

    Output voltage is give b( the for#ula

    Vout= 5(1 + VR1/R1) + (Iq * VR1')

    where %2 is t(picall( about 3#+ 0&003+/ ad V4'* is that fractio of V4' i use, so with 4' 'k

    ad V4' 'k, the #axi#u# theoreticaloutput of over '6V allows for so#e adverse tolerace o

    the resistors ad regulator& +s said, (ou*ll be luck( to get over '0&5V fro# a '6V suppl(&
  • 8/12/2019 Adjustable Linear Regulators (reguladores de tenso)



    Construction Guide Component side view

    1 2 ! 5 " # $ % 1& 11 12 1 1! 15


    2 0V !' '

    ! V4'b/

    ! '6V 4egi/ '

    5 4egc/ 4' ! V4'w/

    " Var9 4ego/ 6 !6

    # !3 V4'a/

    $ 0V !' 6 !3

    % !6 4'

    %*ve used a piece of stripboard : strips wide, '5 holes log which icel( suited the screw;ter#ial

    blocks ad heatsik used, a Maplis 4

  • 8/12/2019 Adjustable Linear Regulators (reguladores de tenso)


    The ter#ial blocks % get fro# [email protected] Mapli sell si#ilar 6;wa( 5&08## pitch but theirs are #uch

    #ore expesive& Or it #a( suit (ou to solder wires direct to the board ad take the# to a #olex

    suppl( ad fa coector&

    heck the fiished board for a( errors or solder bridges betwee tracks, fire up ad test&

    arts List4g' LM7805 5V regulator

    ' 0$ 0&u$/ cera#ic or fil#&

    6 '00$ 0&'u$/ cera#ic or fil#

    4' 'k 0&65. 5E or better

    V4''k li, '-## F?;#outig


    MiscTO660 heat;sik G paste, coectors,

    cotrol kob to suit&

    The #ore co##ol( used but slightl( #ore expesive/ ad!ustable regulators such as theLM'7or

    L600are essetiall( si#ilar, the LM'7 beig at heart a '&65V regulator, the L600 a 6&77V device&

    Their advatages over the 7805 iclude higher curret hadlig up to '&5 a#ps with a '7T, 6+

    with the L600/, a #uch lower 2uiescet curret %2, ad a lower #ii#u# voltage, though that*s of

    little iterest i a fa cotroller&

    Most published regulator circuits give a output dow to the #ii#u# possible 1 with fa cotrol

    there*s little poit i goig below about -V, as (a)the fa #a( ot start ruig at lower voltages,

    ad (b)(ou*re wastig a lot of potetio#eter track that could be used for better sesitivit(& +ddig a

    fixed resistor i series with the pot achieves this&

    The LM'7 has a 4eferece Voltage of '&65V betwee the output ad ad!ust#et pis, ad with the

    circuit show, i si#ilar vei to the previous exa#ple,

    Vout= 125(1 + R2+VR1' / R1) + (Iq * R2+VR1')

    +s said, the %2 value is ver( #uch lower t(picall( 50u+ &00005+/ ad ca usuall( be igored i

    calculatig the output&
  • 8/12/2019 Adjustable Linear Regulators (reguladores de tenso)


    .ith the values show i the circuit above, the calculated output will be fro# -&5V up to ''&7V,

    ideal for fas& The resistor co#biatios for other output voltages ca be calculated with this '7

    [email protected] for exa#ple, #akig 4' 6004 ad 46 -804 will give a 5&5V1''&8V rage with the

    'k pot&

    +s poited out earlier, so#e volts are lost across the regulator trasistor !uctios, so fro# a '6V

    iput the output is li#ited to aroud '0v i a( case (10.25V on mine, with a 0.2A fan)& %*vedesiged for ''&7V because potetio#eters have a prett( broad tolerace rage H60E is co##o/,

    so there*s a bit of leewa( if the actual pot resistace is o the low side of o#ial&


    arts List

    %' LM'7T

    ''00 0&'u$/ '-V cera#ic or #(lar


    6 'u$ '-V tatalu# bead

    4' 6304 0&65. 5E or better

    46 'k 0&65. 5E or better

    V4''k li, '-## pcb #outig


    Misc TO660 heat;sik G paste, cotrol kob

    Construction Guide Component side view

    1 2 ! 5 " # $ % 1& 11 12 1 1! 15

    1 0V ' !'2 br/ 46 !6 V4'

    '6V ' 4egi/

    ! $a9 69/ 4' 4ego/ br/ !6 V4'

    5 4' 4ega/ 46

    " $a1 61/ !' V4'

  • 8/12/2019 Adjustable Linear Regulators (reguladores de tenso)


    The circuit was built o a piece of veroboard, 7 strips wide, '5 holes log& Two track cuts as show

    b( the red spots&

    + 0&65I -##/ drill bit ca be used to #ake these, a few turs b( had will re#ove eough copper

    to break the track&

    % used a sli# coductive pol(#er potetio#eter for V4' but a '-## F?;#outig carbo t(pe

    will [email protected] the lik ad resistor, if ecessar(/ will go uder the pot barrel&

    The '7T re2uires a heat;sik 1 a 65>. t(pe will ru fas rated at up to about '0. at '6V/ as at

    the worst case it will be droppig -V at 0&36+, i&e& 6&5.&

    % like the Mapli 4

  • 8/12/2019 Adjustable Linear Regulators (reguladores de tenso)


    Fhoto shows a earlier desig to use up so#e rather log heat;siks 1 % had to bed the regulator

    legs to fit a drive ba(, the Mark6 is si#pler to build ad eater&

    Lo ,ro-.ut Regulators

    + #a!or drawback of the '7T ad si#ilar stadard regulators is that '&716 volts are lost fro# the

    '6V suppl(, so the fa ca ol( ru up to about 85E of its full speed ad flow ratig& +lthough this

    site is ai#ed at keepig oise dow, there #a( be occasios whe (ou wat to tur the wick right


    ou ca get #uch earer the '6V iput with the ewer low;dropout regulators, ad with the

    cotroller show below #( voltage loss ruig a 600#+ 6&3./ fa was ol( '0#V '6V i,

    ''&87V out, ::E full speedN/&

    The( cost a fair bit #ore tha the hu#ble '7T 1 4apid Alectroics price for a M%6:'56 is &'0

    co#pared to 8p for a '7T 1 but whe (ou factor i the other parts, especiall( with a fac( cotrolkob, it*s ot such a big differece overall, ad well worth it %MCO&

    %*ve used Micrel*sM%6:'56?T regulator, which is rated at '&5+ ad co#es i a 5;pi TO;660

    case& %f (ou eed #ore curret, the M%6:06?T is idetical but rated to +, or the si#ilar

    M%6:506?T will carr( 5+& ou #a( eed a bigger heat;sik with the bigger bo(s& Dee the heat;

    sik pagefor the details&

    Klike the '7, the 4eferece Voltage is across 46, ot 4', ad the calculated voltage output is

    Vout= 12!(1 + R1 + VR1 / R2)

    .ith the resistors show, the calculated output rage works out at -&:V to '6&5V, givig a bit of

    headroo# if co#poet toleraces ru the wrog wa(& (The 20! tolerance ban" on #ots can #la$

    ha%oc with calc&lations ' if $o&r 10k #ot is below abo&t k $o& won*t get the f&ll #otential. The

    ratio of (+1V+1)+2 m&st be o%er ./1 ' increase +1 to 12k or re"&ce +2 to 2k)

    The two capacitors esure stabilit(, particularl( useful with log suppl( leads& Do#e alterativeresistors are give below to suit differet #ii#u# voltages&
  • 8/12/2019 Adjustable Linear Regulators (reguladores de tenso)



    arts List

    4eg' M%6:'56?T

    ' '00 0&'u$/ '-V cera#ic

    6 '0u$ '-V alu#iiu# electrol(tic4' '0k 0&65. 5E or better (see below)

    46 6k6 0&65. 5E or better (see below)

    V4''0k li pot, '-## pcb #outig (see


    MiscTO660 heat;sik 60165deg./ G

    paste, cotrol kob

    Construction Guide Component side view

    1 2 ! 5 " # $ % 1& 11 12 1 1!


    2 '6V 4eg'/ !' ' br/ ! V4'

    4eg6/ !'

    ! 0V 4eg/ !6 ' br/ 4' ! V4'

    5 $a9 4eg3/ 69/ 4'

    " 4eg5/ 46 V4'

    # $a1 !6 61/ 46

    The stripboard is 7 rows x '3 colu#s, two track breaks as show i red& ?ed the regulator leads

    carefull(& % foud the best wa( was to support the outer legs as ear the case as possible with a

    thu#b;ail ad bed outwards slightl(, the support agai o the other side ( &se a "art ti#, also

    %er$ &sef&l for c&rling resistor or "io"e lea"s for %ert

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