Hi all,

i have designed the circuit using MC34063AD
to produce -5V at the output for +5V input.This -5V used to give the supply to multiplexer
i designed the circuit as per the datasheet
I have calculated the resistor R2 and R1 as per the formula
Vout=1.25(1+R2/R1)
Hence i got that R2=8.2K and R1=2.7K
L=100uH,Ct=470pF,R sense=240ohms
but i got only -0.2v at the output
can any one suggest me what was the wrong in my circuit?
Thanks in advance...

 

Hard to help without a schematic.
Please post your total circuit.

 

thanks for your reply..here i have attached the schematic..but the values mentioned above

 

Perhaps you've lost a decimal point . If Rsense = 240 Ohms the circuit will shut down if you try to draw more than a few mA output current. In the datasheet circuit Rsense = 0.24 Ohms !

 

oh k ..but i got the -5v as the output if the R sense value as 10 ohms

 

Good. But the current will be limited to about 30mA. If you need more current, reduce the Rsense value.

 

k..thanks for your reply..actually the maximum output current will be given that 50 mA..
this 30mA is the current which has been reduced in the input side...is it right?
in my case i got that 43.5mA as the output current