current-mode boost converter UC3845

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Hi,
Datasheet says:

Klaus
 

turn on your fets slower to reduce radiated noise - try 33 ohm for starters ...
 

pcb design as attached
 

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thank you all
can i use pcb trace as shunt resistor?i need two 0/008 ohm resistor for current sensing.can i use 10mm length and 0/8mm width trace(0/008 ohm resistance and 0/4 watt losses) as current sense resistor?
 



i made this circuit with all the components used instead of the current sense resistor

at the source pin of the the mosfet. wound the inductor choke myself. the circuit input is 9vdc

and output is 48vdc but the trimmer indicated in the diagram when connected to pin # 2-Vfb of uc3843

the oscillator stops. when disconnect from pin # 2 start oscillating give output of 48vdc.

i don't know the reason why the oscillator stops when trimmer connect with Vfb with no output voltage.

- - - Updated - - -



this is the PCB layout of the boost converter circuit. with trimmer not working.
 

too few volts into pin 2 perhaps? it is designed to see 2v5 from the output divider at all times ....

a soft start ckt would be a good idea too ...
 

with Vout = 48vdc. if the trimmer is set to the bottom then the voltage at Vfb = 3.1 volt.

for Vfb = 2.5v by setting the trimmer at the bottom mean 10k + 4.7k = 14.7k in series with 0.8k.

but i want to change the output voltage to 14vdc using the trimmer which is not working.
 

you cannot have Vout < Vin due to the diode - you need to have a load on the o/p to test properly ...
 

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