Adjustable Linear Regulators (reguladores de tensão)

8/12/2019 Adjustable Linear Regulators (reguladores de tensão)

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Adjustable Linear Regulators

The Other Voltages page 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 datasheet ad %*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# theoretical output 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(&

http://www.cpemma.co.uk/diodes.html

http://tomshardware.co.uk/2004/12/13/zalman_cnps7700/page4.html


http://www-s.ti.com/sc/ds/ua7805.pdf


http://www-s.ti.com/sc/ds/ua7805.pdf

http://www.cpemma.co.uk/diodes.html



Construction

Construction Guide – Component side view

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

1

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<77= rated at '&5>.& ?olt the regulator to the sik with a

thi s#ear of ther#al co#poud i betwee before asse#bl(& .ith a differet sik do a dr(;ru

first to check ever(thig fits&

The heatsik will be electricall( coected to the regulator*s *co##o* pi so #ust ot touch the

liks or other case #etal& <o track breaks are eeded&

apacitors with 5## pitch leads are a perfect fit@ the 0$ #a( be hard to fid 4apid Alectroics

have the#, '0;6--/ but (ou ca use a 660$ or 370$ istead if ecessar( which Mapli have i

#ultila(er pol(ester fil#, BT::C or BD80?/&



The ter#ial blocks % get fro# 4apid@ 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

potetio#eter

MiscTO660 heat;sik G paste, coectors,

cotrol kob to suit&

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

L600 are 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&

http://www.national.com/pf/LM/LM317.html


http://eu.st.com/stonline/books/pdf/docs/1318.pdf


http://eu.st.com/stonline/books/pdf/docs/1318.pdf



.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

alculator @ 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&

Construction

arts List

%' LM'7T

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

fil#&

6 'u$ '-V tatalu# bead

4' 6304 0&65. 5E or better

46 'k 0&65. 5E or better

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

potetio#eter

Misc TO660 heat;sik G paste, cotrol kob


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'

#

http://www.cpemma.co.uk/317calc.html






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 fit@ 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<77= t(pe show o the photo at the botto# of the page, the(*re rated at'&5>. but ver( eat ol( 60## tall/, or their clip;o JK50A is cheaper ad at 65>. is

suitable for a lot of faage& (More on choosing a heat-sink)

$it the heatsik ad dr(;asse#ble the other co#poets to check there*s o iterferece, the cut

the tracks ad start solderig, lowest co#poets !u#per liks, the 46, etc/& %f there is a( dager

of the heatsik touchig the !' lik it ca be #oved to colu#s 6, 3 or '3&

heck the polarit( of the tatalu# electrol(tic 6 before solderig 1 there*s usuall( a plus sig 9/

ad a lie b( the positive lead&

Oe warig 1 the tab of the '7T is coected to the regulator*s output pi, so do*t allow the heat;

sik to touch a( grouded #etal case parts, circuit;board liks, etc, or a short;circuit will occur&

http://www.cpemma.co.uk/heatsink.html





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

up&

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*s M%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 page for 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&

http://www.micrel.com/



http://www.micrel.com/





Construction

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

below)

MiscTO660 heat;sik 60165deg./ G

paste, cotrol kob


1 2 ! 5 " # $ % 1& 11 12 1 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 %ertical mo&nting) ad bed i to fit& The 6 G 3

leads eed less bed, agai support with a dart or fie screwdriver& Test for fit i the stripboard ad

faste o the heatsik&

ut-ut Range it0 arious resistors

4' V4' 46 Mi output Max



output

0 '0k 'k '&63v '&-v

3k7 '0k 'k5 5&'v '&3v

-k8 '0k 'k8 5&:v '6&8v

8k6 '0k 6k -&v '6&5v

'0k '0k 6k6 -&:v '6&5v0 37k 5k' '&63v '6&7v

'8k 37k -k8 3&5v '&'v

k 37k 8k6 -&6v '&v

37k 37k '0k 7&'v '6&:v

3k 50k '0k -&-v '6&7v

Br(;ru asse#ble the co#poets to esure othig fouls o the potetio#eter or heat;sik, the

#ake the track breaks ad solder up, lowest co#poets liks/ first, fiishig with the regulator&

heck carefull(, especiall( for a( solder bridges@ a #ulti#eter with bu))er cotiuit( check is

had( for this, or a #agif(ig glass&

ou ca use a rage of other resistors i the 4'1V4'146 chai to give differet #ii#u# outputs,

or to suit available potetio#eters@ so#e exa#ples are give i the table right, or (ou ca work (our

ow values out usig the above for#ula& %t*s o proble# usig '00k or 370k pots, !ust #ultipl( each

resistor b( '0& $or the #ii#u# output, '&63V, use a wire lik istead of 4'&

Of course, (ou wo*t get over '6V output fro# a '6v suppl(, but the headroo# allows for so#e

co#poet tolerace&

This regulator ca also be used with high;value <T ther#istors i a ther#al cotroller, usig thether#istor i place of 46 ad a suitable pre;set potetio#eter for V4'& $or a '00k P65>

ther#istor Mapli 405$/, 4'9V4' set to 370k would give outputs of 5&8V at 60>, 7V at 65>,

:V at '> ad full;speed at 7>, so 4'30k, V4''00k would be o the butto for fie tuig&

%f (ou wat to check differet ther#istors, there*s a Axcel spreadsheet dowload for the L600

regulator that ca be adapted, with the co#plex for#ula show here icorporated&

in.ut o3-arison

Fi M%6:'56?T M%6:3'+?T

http://www.cpemma.co.uk/l200c.zip

http://openwin2%28%27thermistor.html%27%29/

http://www.cpemma.co.uk/l200c.zip

http://openwin2%28%27thermistor.html%27%29/



' Aable +d!ust

6 %put Dhutdow

Qroud Qroud

3 Output %put

5 +d!ust Output

There*s also a M%6:3'+?T low drop;out regulator, rated at '&65+ ad a fair bit cheaper '&:7/,

but the pi;out is totall( differet, as show right, so it wo*t work i the above la(out& %t also has

o big brothers as alteratives, though '&65+ is ade2uate for #ost fa;cotrol purposes&

Otherwise the circuit is virtuall( the sa#e, the ol( differece beig that the 6:3' IDhutdowI pi

is coected to groud but the 6:'56 IAableI pi is coected to Vi for or#al IOI operatio&

The resistor values used above will give the sa#e results, withi a few #illivolts&

The 660$ 0&66u$/ capacitor ' is reco##eded if suppl( leads are over '0I log which covers

ever( FDK %*ve see/ ad 6 ca be a( value over '0u$, alu#iiu# or tatalu#&

Other eeded parts are as the above list, ad agai the alteratives will work as detailed&

4apid Alectroics ad 4D o#poets stock all the Micrel LBO regulators #etioed, Mapli

do*t do a(&

(to be contin&e")

4ied Regulators

http://www.micrel.com/_PDF/mic2940.pdf

http://www.micrel.com/_PDF/mic2940.pdf



Standard fixed regulator circuit

%f the 7;volt Trick is too drastic a power reductio, a se#icoductor regulator ca be used for a

higher voltage& $ixed output 8V ad :V desigs are #ade, but #a( be hard to fid ador

expesive& Cowever, the cheap ad co##o 7805 5V '+ regulator ca be wired to give other

voltages&

% the stadard circuit, the Ico##oI ter#ial goes straight to groud ad the output is 5V&

ote the "io"e across the reg&lator is o#tional ' it #rotects the reg&lator against re%erse %oltage

from 2 or the loa" if the s&##l$ si"e is shorte" to gro&n".

The regulator should also be fitted with a s#all heat;sik, such as Mapli*s 4<83$ 60deg./&

Output adjusted by resistors

%f the voltage at the Ico##oI pi is raised above groud, this is added to the 5V regulator output,

up to a li#it about 6V below the iput voltage 1 so a '6V suppl( ca give 5;'0V output to fas&

Text;book #ethod show is with a two;resistor potetial divider o the output& Voltage across 4' is

5V, which produces a curret of 54' a#ps& This, plus the regulator*s curret fro# the Ico##oI

ter#ial 2uiescet curret %2/, flows through 46 producig a voltage across 46 of 4654' 9 %2/

volts& This voltage across 46 is added to the 5V across 4' to give the raised output voltage&

$or#ula for the output voltage Vo is



Vo = 5 + R2(5/R1 + Iq)

which rearrages to

Vo = 5(1 + R2/R1) + (Iq * R2)

%2 is t(picall( about 3#+ &003+/, so if 4' is 630 oh#s ad 46 is '50 oh#s,

Vo = 5(1 + 15&/2!&) + (&&! * 15&) = $#V

To #ii#ise the effect of %2 variatios betwee regulators, the divider curret eeds to be

sigificatl( higher tha %2, so 4' should preferabl( be uder 0 oh#s&

heck the output with a #ulti#eter, as s#all chages i %2 fro# oe regulator to aother have a

sigificat effect& Or use a 660;oh# preset potetio#eter for 46 ad ad!ust as re2uired&

Output adjusted by zener diode

+other si#pler #ethod is to use a )eer diode to raise the groud ter#ial voltage, the the output

is

Vo = V6ener + 5V

The ?"88?"R55 series 0&5. )eers co#e i a rage of values betwee 6&7V ad 5&'V givig

7&7;'0&'V fro# the regulator&

The resistor 4' is preset to produce eough curret to #ake sure the )eer is well o, ad #a(

regulators will work fie without it (3 is eno&gh)&



70e #.olt ooler 4an 7ri89

%f a case fa is fitted with a 3;pi Molex #alefe#ale pair of coectors, it*s a eas( ad free

#odificatio to ru it at a lower voltage&

The 3 wires carr( 9'6 volts (ellow/ ad 95 volts red/ supplies with two 0 volt grouds black/ &

The fa leads are or#all( coected to the (ellow ad a black wire for the stadard '6 volt suppl(,

but if coected to (ellow ad red the fa sees '6 ; 5 7 volts&

Oe wa( to re#ake the coectio without the eed for solderig is

'& .orkig fro# the ope eds of the coectors, getl( press i the two barbs o the Molex

pis coected to each ed of the black 0V/ wire that the fa*s black lead coects to& Kse a

fie;bladed !eweller*s screwdriver or a sewig eedle& Bo*t overdo it ; the barbs !ust eed

bedig flush with the pi bod(&

6& The pis should ow slide out the back of the coector& Bo the sa#e for the pis at each

ed of the red 5v/ wire&& <ow getl( bed out the barbs agai, swap the two wires over, ad push the pis back ito

the Molex housigs util the( click ito place& heck first the(*re the right wa( roud, sa#e

as the origial pis&

3& %t*s worth #arkig the coector with a I7I so (ou kow it*s bee altered&

That*s itN The coector ca still be used to power disk drives or a cd;ro#, ol( the wire colours

have chaged& Aach coector pi ';3 still carries the correct voltage&

heck the fa starts reliabl( with the reduced suppl(, as it could ow be ver( difficult to hear that afa*s ot workig @;/

%f (ou wat #ore a bit #ore cotrol, check out how to switch;operate the two suppl( voltages i

this excellet Ihow;toI at ?it;Tech&

http://www.bit-tech.net/article/52/3

http://www.bit-tech.net/article/52/3



+s a securit( agaist the fa ot startig at the lower voltage, (ou ca add a capacitor ad diode to

the 7;volted circuit as described at www&o#ad&ee

.he the co#puter is first switched o, the u;charged capacitor is at groud potetial& Do the full

'6v of the suppl( is iitiall( developed across the fa #otor, esurig it starts&

+s the capacitor charges up, the voltage across it rises to about 5&8v 5v plus the 0&8v forward

voltage for a '<300' diode/, whe curret ca flow through the diode to the 5v rail& The fa eds

up ruig at -&6v& Ksig a schottk( diode eg '<58'7/ with a Vf of aroud 0&3v, the fa would ru

at about -&-v&

The %ast ma4orit$ of fans will start 3&ite reliabl$ at /%, so this is 4&st a bit of ins&rance - neat trick,

tho&gh.

http://www.nomad.ee/micros/quietpc.shtml

http://www.nomad.ee/micros/quietpc.shtml

Documents

Adjustable Linear Regulators (reguladores de tensão)