charge pump help need

Discussion in 'Homework Help' started by hertz.12, Feb 13, 2016.

  1. hertz.12

    Thread Starter Member

    Apr 25, 2015
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    0
    hi
    i want step up voltage from 3.3v to 6v...so i made charge pump but i put 2222 transistor instead of diode...now every thing work fine and i have 6.1 volt ..no problem with circuit...but i am afraid that the transistor may be damage because the "Emitter-Base Breakdown Voltage = 5v" i am really don't understand what Emitter-Base Breakdown Voltage are???

    here is my circuit

    pump.jpg
     
  2. WBahn

    Moderator

    Mar 31, 2012
    18,295
    4,968
    Emitter-base breakdown voltage is exactly what it says. If the emitter-base voltage exceeds 5 V, then it may break down and start conducting current.
     
    jjw likes this.
  3. hertz.12

    Thread Starter Member

    Apr 25, 2015
    36
    0
    so i have to put Schottky diode between the transistor and the cap to protect the Emitter from exceeds 5 V

    sure?
    it works fine now and nothing happen to 2n2222

    thanks
     
  4. WBahn

    Moderator

    Mar 31, 2012
    18,295
    4,968
    At what point does Veb exceed 5V now?

    Have you looked closely at your output voltage on a scope?
     
  5. hertz.12

    Thread Starter Member

    Apr 25, 2015
    36
    0
    hi
    i don't have a scope....voltmeter only
     
  6. crutschow

    Expert

    Mar 14, 2008
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    3,519
    Put the diode in series with the base.
    That way you will still protect the emitter but won't reduce the output voltage.
     
  7. hertz.12

    Thread Starter Member

    Apr 25, 2015
    36
    0
    and the emitter will not damage? that will protect it for sure?
     
  8. jjw

    Member

    Dec 24, 2013
    175
    32
    I don't understand how the circuit could work, the base is floating and the transistor never conducts.
    Is the diagram correct ?
    What is the 20Hz voltage on the base ?

    Edit: Forget the former sentence about the base, but this circuit won't charge or pump :)
     
    Last edited: Feb 14, 2016
  9. jjw

    Member

    Dec 24, 2013
    175
    32
    To double the voltage, Q1 must be a PNP transistor, emitter to +3.3V, from collector a diode to another capacitor, the base voltage pulsing from 0 to 3.3V.
     
  10. crutschow

    Expert

    Mar 14, 2008
    13,913
    3,519
    Yes.
     
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