Parallel voltage regulator

[tim90]

Hi,to everybody, i am using this circuit in the picture

The main problem is related to the two resistors R3 and R4 (to balance the two outputs), because since the maximum current is 15A, i have a voltage drop across the resistor (15A*0.01OHM), so the load regulation will be reduced. I already tried to put the feedback resistor (r1 and r2) after r4 but nothing change. Do you have some idea on how to solve the problem?

 

[dr pepper]

I cant help so much with that particular circuit, however if you were to use a reg with current limit you'd be able to do away with the balance resistors, if you mist use the '1083 you could use an op amp circuit to perform a current limit function using a sense resistor and the adj pin.

Note I wouldnt connect the 2 adj pins together, 2 sets of r1/r2 voltage dividers would be better in that circuit.

 

[alec_t]

Why not use the more conventional arrangement of a single regulator IC with a bypass transistor?

 

[tim90]

i need 15A and a very good load regulation. Do yuo think that i can use a bypass transistor? can you suggest my a proper transistor for this purpose? more over i had another idea but i am absolutely not sure about this idea, it is the following circuit, in which the op amp should sense the difference due to the voltage and modify the feedback. I simulated it and it works.

 

[AnalogKid]

Note I wouldnt connect the 2 adj pins together, 2 sets of r1/r2 voltage dividers would be better in that circuit.

Normally I would agree, but he got that circuit direct from the datasheet. Another concern is that he wants 15A from two regulators rated for 7.5 A each. That is zero margin.

i have a voltage drop across the resistor (15A*0.01OHM),

Nope. If the regulators are sharing correctly, it's 7.5A x 0.01 ohm, or 75 mV. Your output error at max output current due to the ballast resistors is 2.35%, but you can compensate for this by increasing R3. Note that output error is not the same as regulation. An output series resistor directly affects output impedance, but it doesn't affect the output accuracy or regulation unless the output current changes.

What are the min and max output currents that this circuit must supply to its load?
What is the regulation tolerance you need? The LT1083 device has a worst case regulation of over 1% at your input and power levels.

Back to your original question, look at the LM317 datasheet for the basic circuit for adding a power transistor booster to a 3-terminal regulator. The innergoogle is full of LM317 boosted circuits to learn from.

ak

 

[dr pepper]

Your on the right lines, however using the op07 as a comparator with the non inverting at the supply voltage I dont think will work in real life.
Configure a dual op amp to amplify the voltage across the 10mR resistor, and apply that to the adj pin through a diode, so the current amplifier shuts off the reg if its o/p reaches reference voltage.
You'll need either a seperate supply for the op amp, or one that can operate with its i/p's close to the + rail.
Also repeat this for the other reg, so they are seperate circuits.