*Boosting 3V to 5V (using discrete components)

Discussion in 'The Projects Forum' started by JUAN DELA CRUZ, Feb 4, 2010.

  1. JUAN DELA CRUZ

    Thread Starter Active Member

    May 27, 2008
    121
    0
    Hi everyone, its been a long time:)

    Well, I was looking for the right circuit to boost 3V from a battery to 5V using only discrete component coz' dc to dc converter IC aren't available here in my country. Can any one help me to design a circuit and meets atleast 80% efficiency?

    Any help would be appreciated. Thank you
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    What is your current requirement at 5v?
     
  3. JUAN DELA CRUZ

    Thread Starter Active Member

    May 27, 2008
    121
    0
    Thank you sir for your reply.
    I need 5V/ 800mA to charge 3.7V lithium-ion battery.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    OK, so to convert 3v to 5v/800mA with an 80% efficient converter, you will need:
    5v/3v*80% = 1.333..Amperes from the 3v supply. Will the 3v supply be able to handle that current without dropping voltage? The lower the 3v supply goes, the more current will be required to charge the battery.
     
  5. JUAN DELA CRUZ

    Thread Starter Active Member

    May 27, 2008
    121
    0
    Yes sir, my battery source is rated 3V7/ 1800mAh.
    I need to charge a Lithium-ion battery thats why I need a approx. 5V to charge it. I need a circuit using common and discrete components.
    Thank you.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Can you get CMOS 555 timers, and P-channel and N-channel MOSFETs?
     
  7. JUAN DELA CRUZ

    Thread Starter Active Member

    May 27, 2008
    121
    0
    Yes sir. Cmos 555 is available as well as the P-channel and N-channel MOSFETs.
    Do you think it is possible do add an LED indicator to indicates the remaining charge of the source battery and at the same time to indicates if the battery being charge is fully charge already?

    Thank you.
     
    Last edited: Feb 4, 2010
  8. JUAN DELA CRUZ

    Thread Starter Active Member

    May 27, 2008
    121
    0
    Yes sir. Cmos 555 is available as well as the P-channel and N-channel MOSFETs.
    Do you think it is possible do add an LED indicator to indicates the remaining charge of the source battery and at the same time to indicates if the battery being charge is fully charge already?

    Thank you.
     
  9. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    You never charge a lithium-ion battery cell with "approx. 5V".
    If the voltage goes above 4.2V then the battery will catch on fire.
    If the charging current is too high then the battery will catch on fire.
    If it is charged too long then it will catch on fire.
    If the battery is discharged too low then normal charging current will cause it to catch on fire.

    Use a battery charger IC that is made for charging a lithium-ion battery cell.
     
  10. bertus

    Administrator

    Apr 5, 2008
    15,638
    2,343
  11. russ_hensel

    Well-Known Member

    Jan 11, 2009
    818
    47
    Sounds like you are using a (aprox 3 v ) battery to change a ( aprox. 3 v ) battery. Seems odd.
     
  12. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    It is odd.
    He is making one battery catch on fire (have you seen the videos of a lithium battery fire on You-Tube?) by over-charging it from a boosted another battery.

    My remote controlled toy helicopters have lithium batteries that are charged from another battery. But the charger works properly and never over-charges.
     
  13. JUAN DELA CRUZ

    Thread Starter Active Member

    May 27, 2008
    121
    0
    @audioguru
    Ok sir.
    So what will be the safe circuit (using Cmos 555 and P-type and N-type mosfet) that can enable to boost 3V7/ 1800mAh from a battery to a specific amount of voltage and current to charge another lithium-ion battery rated 3V7/ 900mAh.

    Thank you.
     
  14. JUAN DELA CRUZ

    Thread Starter Active Member

    May 27, 2008
    121
    0
    Yes sir. Cmos 555 is available as well as the P-channel and N-channel MOSFETs.
    Do you think it is possible to add an LED indicator to indicates the remaining charge of the source battery and at the same time to indicates if the battery being charge is fully charge already?

    Thank you.
     
  15. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Maxim and most other semiconductor manufacturers make battery charger ICs for charging lithium battery cells safely.

    It is possible to measure the loaded voltage of a lithium battery then guess how much charge is remaining.
    it is difficult to determine how much a lithium battery is charged.
     
  16. JUAN DELA CRUZ

    Thread Starter Active Member

    May 27, 2008
    121
    0
    What do you think is the better component needed to boost 3V/1800mAh to 5V
    with at least 80% efficiency if LMC555 is used as the Oscillator
    and mosfet is used instead of a BJT to achieve higher efficiency?
    What will be the value of the mosfet, inductor, diode and capacitor?

    Thank you.


    [​IMG]
     
  17. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Where will you find a Mosfet in your country that turns on with a gate voltage of only 3V?
     
  18. JUAN DELA CRUZ

    Thread Starter Active Member

    May 27, 2008
    121
    0
    0k. I will use BJT instead.
    So, what do you think is the proper value of the BJT to serves my purpose?
    How about the inductor, diode, capacitor?

    Can anyone please assist me here.
    Thank you.
     
  19. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    I don't know why you want to boost the voltage of one lithium battery to a voltage that is much too high to charge another lithium battery.

    Maybe somebody can remember the boost circuit they used 20 years ago before voltage boost ICs were available.
    Maybe somebody can remember the lithium battery charger circuit they used 12 years ago before battery charger ICs were available.
     
  20. JUAN DELA CRUZ

    Thread Starter Active Member

    May 27, 2008
    121
    0
    @audioguru
    Yeah your right sir. .the circuit that I want to build is quite old tech. But that is what I need. To build a boost converter using LMC555 AS THE OSC.
    But dont know what BJT is needed to boost 3V to 5V
    As well as the proper inductor needed.
    Plz. Help me. Thank you.

    @sgt. Wookie
    Sir, LMC555 is available here in my country. Please help me to design a boost converter to serve my purpose. I dont have enough 'know how' regarding this circuit that's why I'am seeking for assistance. Thank you.
     
Loading...