Electronics > Projects, Designs, and Technical Stuff
Ideal buck converter for high current
mariush:
You should be able to change the feedback of the power supply to lower the 12v by 1-2 volts. The psu may even have a trimming potentiometer.
If not look for the voltage reference, probably not a LM431 but something similar... you could then change the resistor values to adjust voltage, but you'd also have to look into undervoltage protections.
If you don't care about efficiency, you could just get some beefy 30A+ bridge rectifiers and parallel a bunch of them on a good heatsink that will have enough thermal mass to keep them cool for 30s-1m (with a fan it should be doable)... you get 2 diode voltage drops on each rectifier, so you lose 1-2v on each rectifier.
For example : https://www.digikey.com/product-detail/en/micro-commercial-co/GBJ3508-BP/GBJ3508-BPMS-ND/2213559
That peaks at 35A ... if you use 6 of these in parallel along a heatsink, you'll get around 15-20A per bridge rectifier... you get 1.2v drop per diode so around 2v drop.
You could put 2 groups in series for higher voltage drop.
They can handle up to 150c ... but basically you could have them on the sides of a heatsink tube and run air through the tube center to dissipate the heat ...
scroll down on this page to where they show to-220 packages on a heatsink... think those bridge rectifiers instead: http://www.kerrywong.com/2018/09/17/inside-an-agilent-66312a-two-quadrant-power-supply/
anishkgt:
--- Quote from: Jay_Diddy_B on August 05, 2020, 05:18:31 pm ---Hi,
Consider that the ADP1850 demo board is designed for the following conditions:
1) Fsw 300kHz
2) Vout = 1.09V
3) The input power is around 55W, this is 4 to 5A
If you modify for 8V output
The Inductors need to be 6 to 8 times more inductance 3.3 to 4.7uH at 30A Higher values if you lower the switching frequency.
The output capacitors on the demo board 2.5V you need to change to 16V parts
At 40A x 8V = 320W
The input current at 12V is now around 27A
Regards,
Jay_Diddy_B
--- End quote ---
No, not going with the eval board specs, So far this is what i've come up with
Freq: 200kHz
VinMax: 12V
Iout per phase: 22A
Vout: 8.1V
Delta iL: 8.8A
RMS Delata iL: 2.97A
Peak iL: 13.2
Inductance: 1.49uH Round it up to 1.5uH
Duty Cycle: 0.675
Rtop: 125k
Rbot: 10k
Rds(on) max worst case highest Temp: 0.01Ohm
RiLIM: 1.8mOhm
R_RAMP: 349K
Css: 1uf
Tss: 0.0923ms
IN CAP I_RMS: 10.3A
Cin_MIN Capacitance: 100.54uf
Having trouble with calculating input capacitor, I can't seem to find a capacitor based on the value.
Siwastaja:
There's nothing advanced in designing in more phases.
You just, instead of a 8V, 100A converter, design a 8V, 25A converter and copy-paste it 4 times.
The only thing to add is to make them run in sync with phase shifts, for example 180 deg for 2 phases, 120 deg for 3 phases, 90 deg for 4 phases, 72 deg for 5 phases... you get the point. For this, you need to create the sync signal for the ICs with phase shifts, if you can't find a fully integrated controller IC that does 4 phases, or a 2-phase control IC with 90-deg phase shifted SYNC OUT, which would allow a simple single wire from SYNC OUT to another chip's SYNC IN to be used for 4 phases with two chips and no extra clock generators.
anishkgt:
--- Quote from: Siwastaja on August 05, 2020, 05:43:43 pm ---There's nothing advanced in designing in more phases.
You just, instead of a 8V, 100A converter, design a 8V, 25A converter and copy-paste it 4 times.
The only thing to add is to make them run in sync with phase shifts, for example 180 deg for 2 phases, 120 deg for 3 phases, 90 deg for 4 phases, 72 deg for 5 phases... you get the point. For this, you need to create the sync signal for the ICs with phase shifts, if you can't find a fully integrated controller IC that does 4 phases, or a 2-phase control IC with 90-deg phase shifted SYNC OUT, which would allow a simple single wire from SYNC OUT to another chip's SYNC IN to be used for 4 phases with two chips and no extra clock generators.
--- End quote ---
The ADP1850 has a SYNC pin but it only accepts input and no out.
anishkgt:
couple of questions regarding the ADP1850 buck converter.
Under ‘Setting the current sense gain’ on page 17 calculating V_CSMAX requires the Rdson_MIN and MAX resistance. Is this RDSon value from the datasheet of the mosfet or something to with the duty cycle. The max is not defined so i presume it is the same like MIN.Then there V_COMMAX where the ton is required. How can i calculate this ?
The duty cycle is Vout/Vin = 8.1/12 = 0.675 which is 67.5% of the time the high side mosfet is ON. 67.5% of 200,000Hz is 130,000. So how can i substitute it to the formula as a time.
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