MC34063AD negative voltage problem

Discussion in 'General Electronics Chat' started by riyashini, Jan 3, 2015.

  1. riyashini

    Thread Starter New Member

    Sep 18, 2014
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    0
    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...
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,000
    3,229
    Hard to help without a schematic.
    Please post your total circuit.
     
  3. riyashini

    Thread Starter New Member

    Sep 18, 2014
    20
    0
    thanks for your reply..here i have attached the schematic..but the values mentioned above
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,781
    1,103
    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 !
     
  5. riyashini

    Thread Starter New Member

    Sep 18, 2014
    20
    0
    oh k ..but i got the -5v as the output if the R sense value as 10 ohms
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,781
    1,103
    Good. But the current will be limited to about 30mA. If you need more current, reduce the Rsense value.
     
  7. riyashini

    Thread Starter New Member

    Sep 18, 2014
    20
    0
    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
     
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