6v regulator is putting out 8v

Discussion in 'General Electronics Chat' started by whiz100, Mar 23, 2010.

  1. whiz100

    Thread Starter New Member

    Mar 23, 2010
    2
    0
    Hello this is my first post, I'm new to electronics and don't know very much so I'm sorry if this question is dumb.

    I have built a circuit but I'm having problems and I think it's because I've not setup the regulator correctly.

    the power (9v battery)enters a 6vreg which then powers a 3.3v ldo.
    the 3.3v ldo feeds into a pic18 uC
    the 6v feeds into a ftdi usb module, a parallax continuious rotation servo, a laser, and a webcam.

    when the servo is rotating all is well.
    when laser is turned all is well.
    I'm using the pic18 adc to read the 10K variable resistor - which doesn't give me consistent results - but not having used an adc before I don't know if this is normal.

    but if I have the servo and laser do their thing at the same time things start to go bad.

    so I started poking around with a voltmeter and noticed the 6v reg, is pushing 8v not 6v.
    I don't have any capacitors for either of the regulators and wondering if this is causing the problem.

    when i turn either the laser on or off the voltage drops about 1v when the laser is active and several volts (perhaps 4v I think) when the motor is turning. there is a npn transistor connecting the pic 3v to the lasers 6v - used as a switch.

    so I so decided to read the datasheets for the parts and see (i didn't read them in depth before because I don't understand them yet - working on it) they recommend both input and output caps.

    before I put the cap. onto the circuit can someone tell it I'm barking up the wrong tree. Or any other information that will help me.


    parts list
    reg v6 - L7806CV
    ldo 3.3v - mcp1700-3302e



    thanks
    K
     
  2. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    You need caps on the regulators. If not, oscillation can become a big problem.
    That may be the cause to all of your problems. The increase in voltage is causing a decrease in current. SO, when both items are operating at the same time, there isn't enough current available. The regulator is using the extra current to output the 8v instead of the 6v.
     
  3. whiz100

    Thread Starter New Member

    Mar 23, 2010
    2
    0
    thank you. I'll see if can squeeze them on tonight.

    Peter
     
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