Voltage regulator

April 24, 2012 aPowerSupply.com 7 comments

7805 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 shortcircuits 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 shortcircuit protection starts to act, is given by voltage sum on R2 and R3. R3 and R4 resistances form a T2 voltage divider.

Shortcircuit protected voltage regulator schematic

This is LM7805 5V dc voltage regulator circuit diagram has not been tested.

Power supply circuits, Stabilized LM7805, voltage regulator

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Written by miloman on April 11, 2010. Reply

well here I am again back where I started 3yrs ago,,I have no formal education in electronics and at my age of 54 have NO desire “physically” to sit in any classroom atmosphere,,however after 27yr contract plumbing career ended from an accident, I found myself ingulfed with time and a sudden intrest in electronics. I built the “JL Naudin” 30KV powersupply fromscratch learning as I went how to read capps and resistor values because I wanted a variable power supply to test ideas of mine and everytime I tried to adjust voltage down on a project using a pot the pot of course would burn from the current, So I wound what later I found out to be availabe,,my own verzion of rheostat using nicrhome wire from a stripped out heating blanket wound on a cpvc pipe and the core of a alkaline battery for a wiper,,,crude but it worked . Still have it, still works but then I found the Naudin PS and built it. I have used it for sometime until the other day when I was testing a froze 12 V fuel pump and not knowing it had froze, I hooked it up and immediately smelt smoke from my supply,,,so upon exam I found I had burned up the 5K pot used to adjust the 2n3055,
I replaced it and started it up again and hooked up an auto brakelight bulb after cking with my multimeter that it operated,,,BURNED up that NEW pot! through further exam I found my LM7812 had also decessed and was allowing all the 60V through to the variable circuit so puzzeled I reexamined the schematics, then went to my data on the 78xx’s and found that the in Voltage was way to high for this regulator,,,but it had worked for 3 years and had never shown signs of over voltage.
How could this schematic have the req of a 75VA2x24V 1.56A transformer and use the 78XX seris regulation ? I haven’t replaced the regulator yet because I thinnn I know what went wrong,,,I never FOUND a transformer in my area with those specs but I did manage to salvage one trans from an old magnovox stereo tv combo cabnet that put out 70V on the multimeter as to the 1.56A I had nor have no idea what amps this transformer puts out but under a resistive load she sure HUMMMS WELL!
MY questIon is; before silicone, what was the circuit used to reduce voltage with discrete parts off the shelf,,, kirchoffs? Voltage dividers?? I would like to be able to say I know how to do this with parts instaed of Regulators, variac’s,or rheostat’s.

Any help out there for a old sore bone would really make me happy! Thanks Ed
- Written by ece on April 23, 2010. Reply
  
  Can I get me half my homework
Written by dhruv on September 17, 2010. Reply

hello….can i make this project for my college work? because it denotes that this circuit is not tested….thank u for answer…
Written by Bill on March 7, 2011. Reply

HI Miloman.
From an electronic technician who dabbles in plumbing to a plumber who dabbles in electronics.
In the olden days crude regulation was achieved by driving transformers into saturation. Magnetic saturation that is. As you may know, the secondary voltage is produced by a change in magnetic field in the transformer core. If the primary current drives the core into saturation, more current will not produce stronger magnetic field, and a reduction of primary current may still cause field saturation. So the secondary induction is from zero to saturation and back to zero.
These transformers run pretty hot.
You also had not idea of the watts capacity of your transformer. There is a formula for calculating this by the area of the transformer center core. Bigger area= more watts.
Written by Your namewaqas on April 22, 2011. Reply

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Written by nityadeep on July 27, 2011. Reply

sir,plese send me circuit diagram of dc voltage regulator in range of 30-50 volts
Written by nkwenti on November 15, 2011. Reply

Not tested?? i guess it looks like working, the author needs to go back to school and teach us tested and working schematic

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