Goldsmith,
I am still struggling with that boost converter. The IC works OK by itself, but when I apply power to the inductor/MOSFET, it dies...
I took the inductor, MOSFET, diode and two electrolytic caps and imitated what happens when I apply 200kHz to MOSFET.
Yellow graph is the voltage applied to the MOSFET's gate. about 10-12V, 200kHz. The total voltage that I applied to this setup was 120V. The output voltage ranged from 150V to 210V, depending on inductor.
Blue - is the voltage across the inductor.
Green (that looks like triangle on the second picture) - current across the inductor.
I tried 3 inductors between 200uH - 300uH, taken from TV power supply. I do not know if they they had right ferrite or any gaps.
What can you tell me by looking at these graphs? How they suppose to look like?
Can you help me to find where I can buy right inductor? If not, how can I make one?
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About our last conversation - I understand that back-to-back zeners limit the voltage after the capacitor. But I do not understand the benefit of that. If I am going to use a zener after the bridge, why bother to use these zeners? Also you said "don't forget behavior of a capacitor" - what did you mean by that?
Steven
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Goldsmith,
I tried to change the duty of the signal, for an experiment sake, to see if this would affect the waveform.
here are 3 pictures (10% duty, 25% and 45%). I was afraid to go over 50%.
Per my understanding, the current across the inductor should have a triangle form. But it is not...
Is this an inductor issue?
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I have a question for you - is there any way we could communicate a bit more often? Perhaps by E-mail? or it is your internet connection issue?
Steven
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Goldsmith,
I found a web site that helps calculating the value of the inductor for the boost converter. When I entered my data, it suggested a 2,400uH inductor instead of 200uH that was on the datasheet of FAN7340. It also higher than what is calculated using the formula on the datasheet of FAN7340.
https://www.coilcraft.com/dcdc.cfm
Which value is correct then?
Steven
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Update: I think I found what the issue was - wrong inductor. I found a new inductor today (got it from Y-board of Panasonic TV). It was 1mH and it worked like a charm! I finally got the current wave form as it should be!!!
Look:
Green is that desired wave form, blue is the voltage across the inductor. yellow - what goes to the gate and pink is the resulting output voltage. Boy, am I happy!!!!!
That brings me to the question though - how come the final solution was nothing like the formula from FAN7340's datasheet calculated and nothing like the above-mentioned web site calculator produced??? But something in between? By the way, I tried 2.5mH inductor and waveform was not triangle (too much inductance?).
Steven