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Competition #1: Charge Pump Using Astable Multivibrator

Discussion in 'Entries' started by ElectroMaster, Jun 23, 2008.


Do you wish to vote for this Project?

Poll closed Aug 17, 2008.
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  1. ElectroMaster

    ElectroMaster Administrator

    Jul 5, 2002
    Broadbeach, AU
    ***** To vote for this project please answer the poll above. *****

    Project: Charge Pump Using Astable Multivibrator

    LCD text module that is available in most of the country is 5 V type. Recently, many microcontrollers are able to operate below 5 V, and some are limited to only 3.3 V (3.6 V max). If the supply voltage is limited to only 3.3 V, there will be problem interfacing with the LCD module. Usually, boost regulator in IC package is used. Without using any IC, 5 V can be obtained from 3.3 V too.



    Q1, Q2, C1, C2, R1, R2, R3, and R4 form an astable multivibrator to provide oscillation for switching the next stage.
    Q4 is turned on via R4 and R6 when Q1 is off. Then C3 is charged at
    3.3 V – 0.7 V (Vdrop) = 2.6 V.
    When Q1 is turned on, Q3 is turned on too via R7. The voltage appear at the collectors of Q3 and Q4 is approximately 3.0 V (0.3 V Vce drop). With respect to ground, the voltage at the junction of D1, D2, and C3 is pumped up to
    2.6 V + 3.0 V = 5.6 V
    D1 plays an important role here to avoid the current flowing into the supply site.
    This is for one complete cycle, charging and pumping.
    While the next cycle is charging up, D2 and C5 are used to store the current for the previous cycle. The voltage appears at the output is
    5.6 V – 0.7 V (Vdrop) = 4.9 V
    Rload is used as the load. 4.9 V/1.5 k = 3.27 mA which is more than enough for the LCD



    Bill of materials


    PCB layout


    Actual picture


    ***** To vote for this project please answer the poll above. *****
    Last edited: Jul 3, 2008

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