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
This circuit is so easy to make, tanks for this picture
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Can anyone safely say if this circuit works…I built the damn thing but not regulating at the desired 5v, don’t know if I made a mistake or the circuit doesn’t work…Desperate and needs help…need a 5v 3a regulator real soon.reply to my email if anyone has made this circuit work.Thnx alot
guys , i have the same problem , i have found this circuit in “304 circuits” book and i trust , then i designed a PCB and this regulator is part of that , and then boom ! it doesnt regulate correctly , what’s the problem ?!?!
The circiut is unlikely to work, the NPN 2N3055 is shown as a PNP transistor and the collector and emiter are reversed, the 5v regulated o/p of the LM7805 neds to be conected to the base of the 2N3055. Have fun!
T2 is 2N2955, not 2N3055 as you say… And yes, this circuit works.
please help…i made this circuit for my project but problem is that it gives 7.5 v or 3 v constant…..how can i solve it…..is all components are in circuit are placed right?……if any one maid this please help…thank you very much for answering
I have a ultrasonic level sensor that produce the output of 0-5 vlot. I want
to convert this value to the range of 4-20mA? what circuit design is suitable?
Can you please tell me how to i use this circuit to act as a LED driver circuit for a LED of 3W.
there is no one who knows about the problem ?! please
My cranial simulator says it should work. This is how to troubleshoot:
Remove R4 –this appears to be unnecessary.
Remove T1 & T2 and verify that they are indeed PNP transistors.
Now see if it works as a normal 7805 (without T1 & T2). If not, correct wiring problem. I, myself, get the pin-out wrong frequently on regulators.
If it functions as a 7805, reinstall T2 and see if it works OK at high current.
If not, correct wiring problem.
Last of all, reinstall T1. T1 is dormant until the voltage drop across R1 exceeds 0.7V or so. Then it turns on and starves the base drive to T2 thus limiting current to about 3A.
The circuit has very high gain and could possibly oscillate with some components. Adding a capacitor to T2 (base to collector) could possibly tame it. Or add a capacitor across the input, or add a capacitor across R1 as it may be an inductive wire-wound type.
Also, do not expect this to work without a healthy load -perhaps 1A. The minimum load spec for the 7805 is 5mA. With less current, the output voltage may be high.
Thanks alot Mr.Keith , i’ll check it
SHITTY WORK
what volt/amp transformer i use in this project
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.