Solar Charger for Mobile Phone

Discussion in 'Homework Help' started by Yvette_kur, May 24, 2015.

  1. Yvette_kur

    Thread Starter New Member

    May 24, 2015
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    Hi guys, I'm new to this forum, but if someone could help me out that would great!

    I'm designing a solar charger for an iPhone for my circuits class, but my professor won't allow for the use of voltage regulators. This has made it a bit difficult to come up with a working solution.
    My search so far includes shunt regulators, BJTs, MOSFETs, and relays.

    The solar panel is 18V @ 12W, and I don't want to simply throw in a bunch of resistors to dissipate all that energy. The plan is to possibly connect a few USB ports.
     
  2. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    Use 5 volt zener diode?
     
  3. Yvette_kur

    Thread Starter New Member

    May 24, 2015
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    This is what I have so far...
     
  4. shteii01

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    Feb 19, 2010
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    1. You need blocking diode. This diode will allow current to flow from the panel into the iphone. It will block current from flowing from iphone into the panel.
    Do you have one?
     
  5. shteii01

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  6. Yvette_kur

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    May 24, 2015
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    That's my problem. The voltage from the solar panel is variable and if I connect it directly to my phone that could potentially fry my battery (5V @ 1000mA)
     
  7. MikeML

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    Oct 2, 2009
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    If you connected your cell phone to a 5Vdc lab. power supply capable of delivering up to 10A, could that be used to charge it without additional circuitry?

    Why do you need three sets of regulators where one would do it?

    If you make a "series regulator", and the panel is in bright sun, the cell phone is accepting 1A of charging current at 5V, how much power will the series regulator need to dissipate?
     
  8. shteii01

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    Feb 19, 2010
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    That is why you need zener diode.
     
  9. MikeML

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    Where do you get a Zener diode that will dissipate 12W?
     
  10. shteii01

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    I never said that I had one.

    So you are saying that simply sticking zener in there will not work.

    The only other thing that I can think of is to build transistor/op-amp "amplifier" with a gain of 0.42. Op-amp probably will not work, not enough current at the output.
     
  11. Alec_t

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    Sep 17, 2013
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    How does your prof define 'regulator'? Does he mean an integrated circuit which regulates voltage? If not, you're facing an impossible task, since the phone input MUST be regulated to 5V.
     
    anhnha likes this.
  12. MikeML

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    A transistor-boosted Zener diode can dissipate many Watts in the transistor and only mW in the Zener...

    71.gif
     
  13. shteii01

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    My guess they can not use purpose made regulator/chip, 7805 comes to mind...
    Under other circumstances all she would have had to do is panel>blocking diode>7805>iphone.
     
  14. wu.robert1

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    Jun 27, 2013
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    Hi, if we are going from 18V to 5V, you can also look into buck converters.
     
  15. ian field

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    Oct 27, 2012
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    Shunt regulators are quite common in solar applications.

    The TL431 programmable zener can shunt up to 100mA.

    If you need more than 100mA shunt, you can make a hybrid Sziklai pair with the TL431 and a PNP bipolar power transistor.

    Unless you use logic level MOSFETs, some need about 6 - 8V on the gate to switch them on, so could be a bit tricky regulating 5V to charge a phone.
     
  16. estebanzapirain

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    Sep 8, 2015
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    I agree, why don't you just use a 7805? This should provide 5V regulated output. I don't know about efficiency...
     
  17. ian field

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    Oct 27, 2012
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    The standard 7805 has about 2 -3V dropout, so if the unregulated supply falls below about 8V the regulator output ceases. This can be a problem if the charging battery presents its voltage to the regulator output - drive current back in, and the regulator is toast.

    There may be some justification to use one of the LDO variants.

    At least one manufacturer is offering switch mode drop in replacements for 78xx regulators, they're a little bulkier so won't always fit existing equipment. The efficiency claimed for those is fairly typical for a SMPSU design.
     
  18. Morvan

    New Member

    Jun 24, 2014
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    Yvette Kur, there are plenty of Solar Panels with 5V100mA on the market. A good approach could be utilizing one of them. They never get burned your equipment and keep charge at trickle mode (secure charge).
    I have a circuit of solar charger, at my blog, whose you can view just for curiosity, once your magister do not wants it with regulator:
    https://morvlab.wordpress.com/teori...nica-pratica-montagem-de-um-carregador-solar/ (Ptg_Br).
    It uses a 10W Solar Panel and, thanks to a simple LM78?05, regulates from virtutally any current.
     
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