transformerless low cost power supply

8/12/2019 TransformerLess Low Cost Power Supply

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TransformerLess Low Cost DC Power Supply : Resistive & Capacitive:One on the major part of our electronics products is the DC Power Supply that converts mains

AC voltage to a lower DC voltage. Usually we use a step down transformer to reduce mains AC voltage to

desired low voltage AC and then convert it to DC or we use Switched Mode Power Supplies. ut in !oth

cases cost is very high and it ta"es considera!le amount of space. Another #ow Cost alternative for

$ransformer and Switcher !ased power supply is $ransformer #ess Power Supply. $here are !asically

two types of $ransformer #ess Power Supplies.

Capacitive %esistive

$he main difference !etween them is& in resistive transformer less power supply e'cess energy is

dropped as heat across a voltage dropping resistor while in capacitor power supplies voltage is dropped

across a voltage dropping capacitor so there is no energy loss or heat dissipation.

Capacitive $ransformer#ess or Capacitor Power Supply(

)n Capacitor Power Supplies we use a *oltage Dropping Capacitor in series with the phase line.

An ordinary capacitor should not !e used in these applications !ecause Mains Spi"es may create holes in

dielectric of ordinary capacitors and the capacitor will fail to wor". $his may destroy the device !yrushing current from the mains. $hus we use + %ated Capacitor with re,uired voltage is used for this

tas". + %ated Capacitors rated for -/& 0//& 1// * AC and higher are availa!le. %eactance of the voltage

dropping capacitor should !e greater than the load resistance to "eep constant current through the

load.

%eactance of Capacitor& + 2 34-5fC

6here f is the fre,uency and C is the Capacitance. $hus a /.--78 capacitor has reactance of 30.09: on

mains fre,uency ;/. $he appro'imate value of ma'imum current can !e find out !y dividing mains

voltage !y reactance of the capacitor ;since load resistance is small>.

) 2 *4+

) 2 -?/ * 4 30. 0 2 3.@ mA

$hus a /.--78 capacitor can supply a ma'imum current a!out 3mA.As shown 3A fuse may !e used to avoid damages due to short circuit and a MO* ;Metal O'ide

*aristor> also may !e connected as shown a!ove to avoid pro!lems due to voltage transients. $he

resistor %3 is used to limit the high current that may occur during power on. Capacitor C3 --9 ;-.-78> is

used as the *oltage Dropping Capacitor. A leeder resistor is connected parallel to it for discharging the

capacitor when the supply is switched off. Diodes D3 D0 is wired as ridge %ectifier and the capacitor

C- is used to filter the pulsating DC. Bener Diode is used to regulate the filtered DC or you can use )C

*oltage %egulator for !etter results. %esistor %? is used to limit the current through the Bener Diode.

$he following ta!le shows the ma'imum current and open circuit voltage of some commonly used

capacitors.

Capacitor *oltage Current

3/09 0 mA

??09 3/ -- mA

009 3- - mA

109 3* 3// mA

3/9 -0* 0/ mA

--9 -0* 3//mA


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Capacitive $ransformer #ess #ow Cost DC Power Supply or Capacitor Power Supply

Advantages

Significantly smaller in si=e and lesser in weight than transformer power supplies. #esser in Cost when compared to $ransformer or Switcher !ased power supplies. Capacitor Power Supply is more efficient than %esistive $ransformer #ess Power Supply.

Disadvantages


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)t is !etter to use a resistor of dou!le the rated power.

Advantages

Significantly small si=e and less weight than transformer !ased power supplies.

#esser Cost than $ransformer or Switcher !ased power supplies.

#esser Cost than Capacitor Power Supply.

Disadvantages

Eo isolation from AC Mains which introduces many safety issues.

%esistive Power supplies are less efficient as the e'cess energy is losted in the form of heat

across the *oltage Dropping %esistor.

Caution

DonFt $ry this circuit if you donFt have much e'perience with electronics. Care should !e

ta"en while testing or using this circuit. DonFt touch at any points of the circuit since some

points of this circuit is at Mains Potential. After constructing and testing enclose the circuit in a

metal casing without touching PC and metalGcase. $he metal case should !e properly earthed

to avoid shoc" ha=ards.

(1.)Power Supply !DC no transformer$his is circuiut power supply @*DC no transformer&)t easy circuit and small si=e.

*olt output 2 *olt Benerdiode. Output Current 3//mA ;min>.

)t easy circuit and small si=e. Power Supply @*DC no transformer

Hou may "now the reason that ma"e power supply circuit have largeGsi=ed as a result & !ecause

transformer. 6ay this out !e must not use. 6e use capacitor replace as a result wor" also well.

)n Power Supply @*DC no transformer circuit . $he this !ase e,uipment have =ener diodeperform heal voltage !e sta!le or @* DC %egulator. !ut "ind this circuit !e defective that

current not tall sir. $he detail is other & see in the circuit sir.


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(".) DC power supply not use transformer

6or" cycle is C3 and %3 acts reduced AC Current Source to rectifier current is a DC *olt !y!ridge diode circuit which D3GD0 acts to change AC to DC with the C- ma"es the filtering power

DC to smoother will a =ener diode acts to reduce voltage is e,ual to the num!er of volt =ener

diode and C? will DC* voltage output that is more smooth

(#.)$e%ative !ola%e Re%ulator ! not use Transformer

)f friends with loo" for Mini power supply 1* si=es. $hat give negative voltage. ) !egs for to

advise this circuit. )t has prominent smallGsi=ed point and light weight. ecause do not use$ransformer. ut still can use current get /./Amp not e'ceed and when see the circuit. $hin"

use Bener diode control voltage !e sta!le that 1* and have transistor enlarge the trend e,ual to

that want. And still systematically protect through the circuit or Shot Circuit Protect with

$ransistor as well. $he detail is other & see in circuit picture has yes.


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('.) DC Re%ulator supply 1! non transformer

8riends at donFt li"e largeGsi=ed of a transformer. ) !egs for to advise 3*DC regulator powersupply can give the trend current get low a!out /mA not e'ceed. ut enough will usa!le smallG

si=ed circuit has comforta!lely. $hin" ) uses Bener Diode !e formed help maintain oneFs position

volt !e sta!le & and use $ransistor help enlarge current tallly increasingly. Ma"e this circuit is

usa!le well & ut friends as a result must use the carefulness specially & !ecause apply to the

level voltage tall directly yes.

Transformerless Power Supply:One of the major pro!lems that is to !e solved in an electronic circuit design is the

production of low voltage DC power supply from AC to power the circuit. $he conventional

method is the use of a stepGdown transformer to reduce the -?/ * AC to a desired level of low

voltage AC. $he most suita!le and low cost method is the use of a*oltage Dropping Capacitor in

series with the phase line.

Selection of the Dropping capacitor and the circuit design re,uires some technical

"nowledge and practical e'perience to get the desired voltage and current. An ordinary

capacitor will not do the jo! since the device will !e destroyed !y the rushing current from themains. Mains spi"es will create holes in the dielectric and the capacitor will fail to wor". +Grated

Capacitor specified for the use in AC mains is re,uired for reducing AC voltage.

+ %ated capacitor 0// *olt

efore selecting the dropping capacitor& it is necessary to understand the wor"ing

principle and operation of the dropping capacitor. $he + rated capacitor is designed for -/&

0//& 1// *AC. &%ectance

; + > and the Mains fre,uency ; / 1/ are the important parameters to !e considered

while selecting the capacitor. $he reactance;+ > of the capacitor ; C >in the mains fre,uency ; f >

can !e calculated using the formula


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+ 2 3 4 ;- J fC >

8or e'ample the reactance of a /.-- u8 capacitor running in the mains fre,uency / as an

important parameter. )mpedance can !e calculated using the formula

B 2 v % +

Suppose the current in the circuit is ) and Mains voltage is * then the e,uation appears li"e

) 2 * 4 +

$he final e,uation thus !ecomes) 2 -?/ * 4 30. 0 2 3.@ mA.

$herefore if a /.-- u8 capacitor rated for -?/ * is used& it can deliver around 3 mAcurrent to

the circuit. ut this is not sufficient for many circuits. $herefore it is recommended to use a 0/

n8 capacitor rated for 0// * for such circuits to give re,uired current.

+ %ated AC capacitors -/*& 0//*& 1/* AC

$a!le showing the + rated capacitor types and the output voltage and current without load

transformerless low cost power supply

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