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  #1  
Old 04-25-2011, 07:03 PM
jayzac jayzac is offline
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Default Buck Converter MPPT

Below attached my design for buck MPPT
All of the port will connect to pin header and to the microcontroller board. I wish to test this buck converter board individually without connecting to the MCU board. So, the buck is supplied with 18V from DC power supply in order to step down to 12V battery charging voltage. I am giving PWM signal to IR2104 driver at pin 2 using signal generator. However I fail to turn on my NMOS because there is no output at IR2104. After sometime the R7 of 100 Ohm resistor at current sense burned. Is there any problem with the current sense circuit ?

1. Is my way of testing correct?
2. Is my design for buck converter works for MPPT application ?

Thank you
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Old 04-25-2011, 11:39 PM
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russpatterson russpatterson is offline
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I would isolate just the driver section and see if you can get your MOSFET's to swtich the way you expect. I'm working on a similar circuit for MPPT for solar. I gave up on the high-side NMOS for the time being and went with a P-Channel FET. The problem I ran into was generating the voltage higher than my panel voltage necessary for turning on the NMOS. I've got mine working now, (still has some issues but basically it functions). Let me know if you want that schematic.
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Old 04-26-2011, 02:45 AM
jayzac jayzac is offline
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Can i have a look at your design ? Thank you
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Old 04-26-2011, 02:04 PM
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russpatterson russpatterson is offline
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Sure thing. Here's the schematic. I've built this on the bench but am expecting a PCB of this design later this week. You can get the PCB here if you want but it's yet untested. http://www.batchpcb.com/product_info.php?products_id=58595&check=8570465f4 e3d4f44206c587865acb773

Ignore the second MOSFET on there. That's for experimenting with eliminating the diode, D3, for improved efficiency.

So on the tests on the bench I was able to put out 30V on my bench supply and buck it down to 12V (or whatever target voltage I set in the firmware). I've been running it at 5Khz but plan to speed that up.

I've been having a lot of issues due to the sudden current change when I switch off the supply voltage. It causes voltage drops/spikes that my 7805 voltage regulator is not handling well and sometimes resetting the MCU.
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Old 04-26-2011, 05:50 PM
jayzac jayzac is offline
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I wonder if this design is able to run at 50khz ? Because my inductor of 220uH limit my frequency.
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Old 04-26-2011, 05:58 PM
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russpatterson russpatterson is offline
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Good question. I would say, in a simulator, yes. Maybe you might want to eliminate R4, I added that to slow switching as I was getting a large voltage spike on the gate when that switched on. However going with a PMOS with lower gate charge helped that quite a bit.

Things are different on the bench than they are in the simulator, that's for sure. I also have a PCB with just the high side driver circuit (w/out the caps) that can be available on BatchPCB if you're interested. You can build up your circuit and test it.

I'll give it a try at 50Khz but it may be a couple of weeks before I get to that.
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Old 04-26-2011, 06:14 PM
jayzac jayzac is offline
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I am interested with the other approach that you mention about the high side driver. Can i have a look for it please ? Thank you .
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Old 04-26-2011, 08:13 PM
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russpatterson russpatterson is offline
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Sure, the high side driver is part (most) of the design above. Here's the schematic along with links to threads on here that cover the topic pretty well.

http://www.backyardsolar.blogspot.com/

You can order the PCB here. http://www.batchpcb.com/product_info...48c36bff69aeba I have a few extra from my last order so if you're interested let me know and I can get you one with or w/out parts on it.
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  #9  
Old 05-04-2011, 07:31 AM
s.chandrashekar020 s.chandrashekar020 is offline
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Hi all, Am writing C code for MPPT algorithm and got struck in between, please help me to sort the issue. My query is
"For every environmental condition there is a voltage-current array, from which we choose the pair that gives maximum power, I generated this array by varying the duty cycle of the DC-DC buck converter, by assuming its input is not changing while varying and then choose the pair for which am getting maximum power and then giving this voltage-current pair to the battery". But am not sure this is the right way or not, please help me. Thanks in advance.
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Old 05-04-2011, 02:02 PM
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russpatterson russpatterson is offline
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Have you seen this app note from Microchip? http://www.microchip.com/stellent/id...pnote=en536175

I think the idea is that you alter the duty cycle and then calculate the power coming out of your circuit and into the battery or load (watts = current * voltage). You then look for the highest power output. Change the duty cycle every 5 seconds or so and if power goes up, good, if it goes down then go the other direction. You should probably start a new thread though.
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