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    li-ion voltage reducer to 3volt - help needed

    Hi fellas, I have a thing that I should improve any circuit that I design, back adays I've added lithium ion to my wireless mouse and its working fine
    but the thing is the mouse circuit is designed for 3 volt s when the battery at full state is around 4.2 volts
    for solving and reducing this voltage difference I added a diode to decrease voltage
    As you know its not efficient and when my battery is at lower voltage the mouse stops working but I know there's still enough juice. (battery at 3.3v)
    so is there a non-complex way ( considering 1cm*2cm*3cm space available in wireless mouse housing ) to have steady 3 volts at output of lithium battery?
    - also efficiency matters
    thanks in advance!
    Last edited by Javid.zare.s; 15th September 2019 at 01:29.

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    Re: li-ion voltage reducer to 3volt - help needed

    Hi,

    There are linear LDOs.
    And there are switch mode step down converters, also called buck converters.

    All have their benefits and drawbacks.

    But to decide which one to choose, you need to know electrical values, like current, time, battery charge, self discharge rate ... and so on.

    Klaus
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    Re: li-ion voltage reducer to 3volt - help needed

    My wireless mouse takes 3V @ 10mA. I made a battery pack from 2 half-used D cells. 2.5V is sufficient to operate the mouse.

    If your setup is similar then I think a plain zener diode does the job.

    Click image for larger version. 

Name:	3_3v zener diode regul 4V supply to 3_2V 300 ohm load.png 
Views:	7 
Size:	25.5 KB 
ID:	155519

    The supply V is between 3.2 & 4.2V.
    The load gets from 2.9 to 3.4V.
    A small amount of power is wasted.

    The zener voltage can be assembled from a combination of series diodes and led's.

    This is shunt regulation. By adding a transistor you can make series regulation.


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    Re: li-ion voltage reducer to 3volt - help needed

    Quote Originally Posted by BradtheRad View Post
    My wireless mouse takes 3V @ 10mA. I made a battery pack from 2 half-used D cells. 2.5V is sufficient to operate the mouse.

    If your setup is similar then I think a plain zener diode does the job.

    Click image for larger version. 

Name:	3_3v zener diode regul 4V supply to 3_2V 300 ohm load.png 
Views:	7 
Size:	25.5 KB 
ID:	155519

    The supply V is between 3.2 & 4.2V.
    The load gets from 2.9 to 3.4V.
    A small amount of power is wasted.

    The zener voltage can be assembled from a combination of series diodes and led's.

    This is shunt regulation. By adding a transistor you can make series regulation.
    great design, it provides exactly what I was hoping for, clever use of zener.
    the only thing is 10mA draw when idle, that's okay I'll add your design "after" the ON button, so it won't draw the juice
    Thanks mate



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    Re: li-ion voltage reducer to 3volt - help needed

    Quote Originally Posted by BradtheRad View Post
    My wireless mouse takes 3V @ 10mA. I made a battery pack from 2 half-used D cells. 2.5V is sufficient to operate the mouse.

    If your setup is similar then I think a plain zener diode does the job.

    Click image for larger version. 

Name:	3_3v zener diode regul 4V supply to 3_2V 300 ohm load.png 
Views:	7 
Size:	25.5 KB 
ID:	155519

    The supply V is between 3.2 & 4.2V.
    The load gets from 2.9 to 3.4V.
    A small amount of power is wasted.

    The zener voltage can be assembled from a combination of series diodes and led's.

    This is shunt regulation. By adding a transistor you can make series regulation.
    update: I've built it on my project board and seems it's not dropping any voltage, double checked .
    But my simulation app (icircuit) shows it should work( works there as you said), whats wrong here?



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    Re: li-ion voltage reducer to 3volt - help needed

    is the zener really 3.3V?
    increase the input voltage slowly to about 5 or 6 V - does the zener regulate?

    if you take the zener out, what is the voltage at the junction between the two resistors?

    if the voltage there is not greater than the zener voltage, the zener will not turn on
    and there will be no regulation

    how much current does the zener need to regulate?


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    Re: li-ion voltage reducer to 3volt - help needed

    Quote Originally Posted by wwfeldman View Post
    is the zener really 3.3V?
    increase the input voltage slowly to about 5 or 6 V - does the zener regulate?

    if you take the zener out, what is the voltage at the junction between the two resistors?

    if the voltage there is not greater than the zener voltage, the zener will not turn on
    and there will be no regulation

    how much current does the zener need to regulate?
    yes there was a mistake with zener diode selection, I thought my diode is a zener type but it turned out to be a 0.5 watt diode.
    now I placed the zener and everything seems fine. thanks for mentioning it



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    Re: li-ion voltage reducer to 3volt - help needed

    Hi,

    The problem with this shunt voltage regulator is, that it draws a lot of current.
    Li-ion voltage is above 3.6V even when it is discharged to 10% charge.
    This means about 5mA zener current.
    And at 4.2V it draws about 15..20mA.

    Any LDO will be more efficient than the shunt regulator ... making the mouse work longer.

    Klaus
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    Re: li-ion voltage reducer to 3volt - help needed

    I second KlausST's recommendation of an LDO (low drop-out regulator). There are many types available but some of them consume an appreciable amount of current in addition to the load. For example, the popular AMS1117 consumes 5mA by itself.

    The Holtek HT75xx-1 consumes just 2.5µA which is negligible compared to that used by the mouse. It has a drop-out voltage of 0.1V which means that it will still put out 3V even when the battery voltage has gone down to 3.1V. The mouse will probably continue to work even below that for some time. The xx in the type number stands for the voltage. Thus HT7530-1 is the 3V version.



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