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Help for Boost Converter

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edmond_chan85

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boost converter formulae

I am trying to build a boost converter. The scope of my project is that the input voltage is variable (8V to 23V) and the output is constant (24V). I am using PIC16F877 as the switching part and MAX627 as the MOSFET driver. The switching frequency is 20kHz and my boost converter should be able to run until 100W.

Problems occurred when I test my circuit with load. During low load condition R=165ohm(I'm using pure resistive as load), the output voltage is correct and runs according to calculation and formulas. But when I tried with higher load R = 25ohm, the output voltage starts to distort(spike/overshot) and voltage drop occurred. The circuit not run according to the formulas (Vout= Vin/(1-k) ). My major problem is that the voltage waveform is not smooth.

Anybody can give ideas?I had stuck in this problem for few months. Thanks.
p/s:I had attached my design circuit for easy understanding.
 

eem2am

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not foundnot found1

thats very low frequency.

maybe you just download switchercad from linear.com and open up their test fixtures and see how it works for nothing
 

edmond_chan85

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boost converter

thanks for your information. I had tried to increased the frequency but it seems nothing different to my output voltage waveform compare to earlier. By the way, am I using the right power MOSFET?should my MOSFET working in linear region or saturation region?
 

sakthivel.eee

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HI
I think by increasing the load, u r operating at discontinuous mode. Try to reconsider ur inductor for the specific low current that u try.

Sakthi
 

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