Hot Issue-Only battery charging operation with charger

Discussion in 'The Projects Forum' started by mishra87, May 19, 2016.

  1. mishra87

    Thread Starter Member

    Jan 17, 2016
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    Dear All,

    1. If only charger is connected without battery, the instrument should not work.
    2. If charger and battery both connected, it should work.
    3. If only battery is connected, it should work.

    Schematic attached and Footprint denotes-

    1. J25- Charging jack and charger is connected with this point.
    2. U18- LTC4057 charging IC
    3. U20- FDS6375
    4. SW5- ON/OFF switch
    5. J22- Pin 1 and 2 connected with battery. Pin1-: +bat and Pin2-: -bat

    Please suggest the changes if any need to be done!!!

    If we look at Smartphone nowadays if we connect only charger and battery is removed, the Smartphone does not work. I want to implement the same things in my application.

    Thanks in Advance !!!
     
  2. JohnInTX

    Moderator

    Jun 26, 2012
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    Last edited: May 19, 2016
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  3. mishra87

    Thread Starter Member

    Jan 17, 2016
    207
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  4. wayneh

    Expert

    Sep 9, 2010
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    ? I don't see any schematic ?
     
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  5. mishra87

    Thread Starter Member

    Jan 17, 2016
    207
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    Can anybody can explain me-

    A battery charger can be used for only battery charging operation.
    I do not want a charger to operate the instrument.
    Only battery battery operate instrument.
    How it can be done...!!!
    Can dual channel MOSFET do the job for same.
     
    Last edited: May 28, 2016
  6. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    You can do that using a switched connector for your battery charger:

    upload_2016-5-28_7-12-52.png

    Thus, when the charger is plugged in, the battery is charged and the device will not operate. When the charger is unplugged, the device operates; however, you can add a second on/off switch for the device, if desired. I use the enable pin of the voltage regulator for that purpose.

    You can switch either the positive or negative, but center = positive is much more common.

    John
     
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  7. mishra87

    Thread Starter Member

    Jan 17, 2016
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    I do not understand your point.

    Lets take a example of smartphone-
    Conditions-
    1. Battery charger + battery= Battery is being charged and meantime smart phone works.
    2. Only battery- Smartphone works.
    3. Only charger(battery removed)- Smartphone does work

    Can it be implemented !!!
     
  8. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    I know of no way to charge a single battery while it is operating a device and have none of the electrons from the charger wander into the device. There will have to be a common ground. In theory, you could rapidly pulse the charging cycles and draw current from the battery only during the periods that the battery charger was not charging. Then that current could be stored quickly in a capacitor to provide relatively DC for the device. However, what do you think that will accomplish? You could also have multiple batteries and use some while the others are charging.

    Please explain why you want to do what you are proposing to do.

    John
     
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  9. mishra87

    Thread Starter Member

    Jan 17, 2016
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    you have misunderstood probably.

    In my application my load is working with charger even if battery is removed.
    I want it should not work with charger.
    As i explained smartphone application.
     
  10. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    OK, I think I understand now. Here is a patent that detects when the charger is connected but the battery is absent. That signal can be used to inactivate the device. However, the charger must deliver a pulsating voltage (e.g., unfiltered DC).

    http://www.google.com/patents/US5422560

    Since that patent is 20 years old, I suspect there may be a chip to do it. I will keep searching.

    John

    EDIT: Here is a device that detects whether a discharged battery is present by applying a trickle charge. If that charge doesn't work, then charging is suspended.
    http://www.linear.com/product/LTM8061
    You could do a similar thing (not necessarily with that device) by having a very low resistance in series with the battery. If no voltage is detected across that resistance, then an intelligent switch would disconnect the device.
     
    Last edited: May 28, 2016
  11. wayneh

    Expert

    Sep 9, 2010
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    It's very easy to set up a comparator to detect the presence of a battery. Control a MOSFET with the comparator output.
     
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  12. mishra87

    Thread Starter Member

    Jan 17, 2016
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    I think this is the way to do...
    Could you share a rough schematic...!!!
     
  13. eetech00

    Active Member

    Jun 8, 2013
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    Hi

    Use a smart li-ion battery charge chip. One that is designed to act as a DC supply (with a power source of course) if the battery is removed. Like the "PowerPath" series of charger chips.
     
    Last edited: May 29, 2016
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  14. mishra87

    Thread Starter Member

    Jan 17, 2016
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    G
    For your kind information I want to let you know that I have already using charging IC LTC4057.

    I think has started going some other way.
    Probably I am unable to make you people understand the exact problem.

    My question is totally different.
     
  15. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Hi mishra,

    Here is my understanding of your requirements:
    Condition: Result:
    1)Battery in place and not connected to charger Device works
    2)Battery in place and being charged Device works
    3)Battery removed and device attached to charger Device does not work

    If that understanding is incorrect, please please correct the states.

    A resistor in series with the battery, as I suggested in post #10 (last sentence), would have a voltage drop across it only when a battery was in place. Polarity of the voltage drop would tell you whether it was powering the device or being charged. So by detecting that voltage, you could produce a signal. That signal could be used to enable the device (e.g., via an enable pin on the voltage regulator). Is that an approach that you want to develop further?

    There is a 4th state you have not mentioned, "battery in place and discharged," that needs to be considered, but I presume you have handled or will handle that another way to avoid over discharging the battery.

    John
     
    Last edited: May 29, 2016
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  16. eetech00

    Active Member

    Jun 8, 2013
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    Yes...but the LTC4057 is not designed to provide the operation you want.
     
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  17. mishra87

    Thread Starter Member

    Jan 17, 2016
    207
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    Hello John,

    you are clear with my requirement. That is what i wanted to implement please find the attached schematic and let me know how can be implemented in the existing system.

    J25- Charging jack
    J22- Battery
     
  18. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Hi mishra,

    Your schematic has the battery charger connected regardless of whether SW5 is open or closed. One option to avoid that is to connect the !SHDN pin to the BAT terminal with a pull down resistor rather than to VCC. Thus, when SW5 is open, voltage at the !SHDN pin should be below the threshold. With a battery in the circuit and SW5 closed, it should enable the charger, assuming the battery's voltage is above the low-voltage lockout value. If the battery is out of the circuit, closing SW5 should not make a difference and the charger will remain shut down. I am not sure what happens if the battery is removed while SW5 is closed.

    I searched briefly on cell phone battery detection circuits. The LTC4078 has such a circuit:
    upload_2016-5-30_6-42-18.png

    Notice that it requires a third terminal on the battery for R4. There is an internal pull-up resistor on that pin. When a battery is not in circuit, the pin goes high and shuts down the charger. If you put a small leaf contact at the positive terminal of your battery holder, you could do the same thing. You could also use a similar leaf spring contact to control the !SHDN pin of the LTC4057. (Remember that the !SHDN of the LTC1054 and BATDET of the LTC4078 work oppositely when held high.)

    I do not have an LTC4057 to test. I would first try it with the simple solution mentioned above. It may work, or it may not. If it doesn't work, then the simplest next approach would be to add the contact to detect battery presence as is done by several cell phone battery charger chips.

    Regards, John
     
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  19. mishra87

    Thread Starter Member

    Jan 17, 2016
    207
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    Thanks john for reply !!!

    We have a product already running in market .
    So i would prefer 1st go ahead with LTC4057. If it can not be implemented then i would try with LTC4078.
    What could be pull up resistor value if i need to connect the SHDN pin of LTC4057 to Battery and please also let me know that whether it suppose to connect with BAT+ .
    SW5 is ON/OFF switch for Instrument .
     
  20. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    I suggested a pull-down resistor. When the LTC4057 is "off", the datasheet shows 2 uA at the BAT pin. !SHDN current is shown as 5 uA. So, a simple connection between the two may be enough to enable the device . A resistor, say 10K from BAT to ground would ensure the device was shut down (2uA x 10K Ω = 0.02V). Now, when the battery is attached, the voltage at the BAT pin would be 4 V or more. The resistor itself would draw 0.4 mA, which is wasted energy, but the voltage at the pin would be enough to enable the charger. I am not sure whether that is a workable solution, as I have no experience with that chip.

    Your schematic didn't show the battery, but it does show "3.7V/700mAh" which I assumed was the battery and power to the instrument was intended to be at CON4, pin1. (BTW, what is the purpose of the FDS6375? If it is a high side switch, the drain and source seem to be reversed. On P-channel mosfets, the body diode is forwarded biased D-->S. Moreover, the gate is grounded, so it should be on all the time. Is there another connection to the gate pin that is before R38?)

    John
     
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