voltage regulator circuit

3 Ampere LM7805 Voltage Regulator

Voltage regulator IC’s, with 3 pins, from LM7805 and LM7812 series are excellent for usage in voltage regulator circuits. If you need higher currents, up to 3 A, you must add a complementary transistor, T2 in this schematic. In a normal design, in case of a shortcircuit, the power dissipation can be very high. This problem can be solved using the voltage regulator design presented bellow.

Through electronics tehniques, when short-circuits occurs this circuit design reduces the maximum current consumption when the output voltage drops. At this voltage regulator prototype the maximum current, with output shortcircuited it was only 0,5 A, so no overheating occured.
In this dc voltage regulator circuit, T1 is for current limitation. As soon as the voltage on the R2+R3 becomes higher than 0,6-0,7 V, T1 opens, which leads to a reduction to zero of the T2 base current. The voltage at which the short circuit protection starts to act, is given by voltage sum on R2 and R3. R3 and R4 resistances form a T2 voltage divider.

7805 voltage regulator circuit diagram

voltage regulator circuit


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  • ander

    hello, transistors
    T1 = BD240C
    T2 = 2N2955
    They not sold in my country, with another transistor can replace

  • V.Sambath kumar

    Hi Chris,

    R1 6.8 ohms, R2 0.22 ohms 3 watts, R3 10 ohms, R4 150 ohms 1 watt.

    c1 and c2 0.1mfd,104j,100k all are same ceramic disc cap or polyster cap. ceramic cap usually fr 50 100v. polyster usually above 100v.

    V.Sambath kumar.

  • Chris

    Can anyone tell me the “R1” and “R2” resistor and “C1” and “C2″capacitor values are in this diagram? I am a novice and don’t understand the way the values for the resistors and capacitors in this diagram are written.



  • gwumex

    please can i use this circuit with a 10v 410ma solar panel? please i nid a reply

  • Anwar Malik

    Hello Mr.Jim Keith
    i would like to know about DC volts auto regulator CIRCUIT
    which works with vehicle RPM pulse voltage, by increasing RPM the regulator should increase DC volts up to 200 volts DC,
    i will be very great full if you may help me,
    best regards
    Anwar Malik

  • Eka Handayani

    Another alternatif. you may want to use SMR8805 from SMR88xx series, its a switch mode replacement for 78xx with higher output current.

  • Jim Keith

    I would use a 12.6VCT @ 2A filament transformer with full-wave center-tapped rectifier configuration using (2) 3A Schottky rectifiers and large input capacitor (47,000UF). This is necessary to keep minimum voltage above 7.5V @ full load.

    Triad VPS12-2000 (DigiKey 237-1256-ND) sells for $7.80.

    United Chemi-con 47,000uf, 16V (DigiKey) 565-2620-ND) sells for $4.00.


    what volt/amp transformer i use in this project

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