Paralleling of power regulators( LTC3780) for high-current applications (600W)

[vishwa062]

One regulator(LTC3780) is having output 12V @10A ,My requirement is 50A, 600W.So i am connecting 5 regulator in parallel. to achieve the high current.

My questions are;

1] Can we connect 5 regulators in parallel through diodes(Power ORing at output side)?. In this case we have to use high power diode.it will be a constraint.

2] Current sharing of 5 regulators how it will be managed?

3] How far it is safe while considering the full load and design.

4] Anybody had a idea regarding this kind of design, please share the information.thanx in advance.

 

[milind.a.kulkarni]

I have one question here....

Are you planning to use 12v output of all the regulator on common bus ?.....if yes...then it is very very tricky....you need to consider the voltage balance and impedance balance between the regulator...bcz in this case if the load increases the requlator with less impedance path will try to feed the maximum current and eventually may burn out even....one more thing is about this idea is you need to have some sense mechanisum for overcurrent protection and voltage control of that regulator such that other regulators will start feeding it.... typically in power system same concept is implemented for load sharing in alternators using governors with the help of speed and excitation controls....

If you don't have common bus requirement then it is as good as using five seperate regulators used on main units.....

may be helpful to you

Good Luck

 

[vishwa062]

I have one question here....

Are you planning to use 12v output of all the regulator on common bus ?.....if yes...then it is very very tricky....you need to consider the voltage balance and impedance balance between the regulator...bcz in this case if the load increases the requlator with less impedance path will try to feed the maximum current and eventually may burn out even....one more thing is about this idea is you need to have some sense mechanisum for overcurrent protection and voltage control of that regulator such that other regulators will start feeding it.... typically in power system same concept is implemented for load sharing in alternators using governors with the help of speed and excitation controls....

If you don't have common bus requirement then it is as good as using five seperate regulators used on main units.....

may be helpful to you

Good Luck

thanx milind for your concern...on my post


These sentences are making me to worry.......

"then it is very very tricky....you need to consider the voltage balance and impedance balance between the regulator...bcz in this case if the load increases the requlator with less impedance path will try to feed the maximum current and eventually may burn out even..."


HOW TO DO THIS.???????

Voltage balance?
Impedance balance?..on board it is going to be a challenge

Is their any idea..to achieve this.Have you did this kind of designs earlier.?

 

[milind.a.kulkarni]

I had read the datasheet of the LTC3780 now ....It have "Foldback Output Current Limiting" ....I think you win the game here....also it have voltage sense too but if I see the current rating it is not exactly 10amp ...see the regulator efficency curve.... i think it will give you out safely 8.5amp at 12v.... In my view you should try out... first two regulator in parallel....for 15 amp...may be load of altest 16amp.....10 ohm 1 amp / 10watts resistors ....i think 15 in parallel for load....if it works....Also I will suggest you have proper heat sink and fans/Air flow ON ....Make sure that the capacitor that you are using should have higher values like 1000uf best will be electrolyte for power design.....
Please put the fuse also in the circuit for protection and monitor the time and temperature of the regulator....should be work....

Good Luck

 

[mtwieg]

For typical current mode converters, using many in parallel is usually not difficult. All you need to do is have all the converters share an error signal (the Ith pin voltage for the LTC3780), and share other things like soft start voltages and other control signals. If that's the case then the current setpoint of all the converters will be the same and they should share current equally and there is no need for output diodes. You would have one of the converters be a master with its Ith pin driving all the other Ith pins (through low impedance buffers, probably).

HOWEVER, the LTC3780 is not a typical current mode converter. Each one can operate in one of three modes, based on vin and vout, and if you want to run them in parallel, then you need to ensure that they all run in the same mode at the same time. However the LTC3780 doesn't give that level of control, so I don't think it's possible. If you try to run these things in parallel, I suspect they will behave very wildly when you try to have them change operating mode.

It's possible that you could use larger FETs and get more power per converter, but the switching frequency only goes down to 200KHz, which probably prohibits going much over a couple hundred watts. But decreasing the amount of stages would help a lot... but again, still might not work at all.

 

[vishwa062]

Hi

""HOWEVER, the LTC3780 is not a typical current mode converter.""


If i use converter of having feature "Current Mode Control". can I achieve it.
So i can choose some other converter with this feature.

 

[FvM]

Referring to mtwieg's doubts, I think there's a chance, that the multiple converters will cooperate in a reasonable way with just parallel connected Ith pins. You won't want to use additional diodes, because they dwart the converter efficiency.

To get full advantage from paralleling the converters, you can supply a multi phase clock signal to synchronize them. This should allow a considerable reduction of total input and output capacitor size.

I agree however also with mtwieg's conclusion, that a converter with discrete transistors is most likely the better solution.

 

[Mehrshad74]

you can easily parallel regulators with current limit function without any sharing circuit.
Assume 3 regulator with 10A current limit and some difference in output voltages and output impedance.
while the load current is less than 10A the regulator with the higher voltage (or lower impedance)will supply the current and others are resting.
when the load current goes higher than 10A it will go to current limit region and its output will drop and now the second regulator will supply the additional current.
when current goes higher than 20A the 3d regulator will wake up.
in this configuration one regulator might work harder than others but it works.