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Thread: Generating 5V power from 3.3V powered PIC

  1. 24th February 2008 02:08 PM #1
    Andy_123
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    Default Generating 5V power from 3.3V powered PIC

    Have a small project with PIC 18F66J60 / Ethernet connection
    It is powered by batteries and 3.3V/200mA generated by TPS60120

    I need to add 5V LCD, so is it possible to generate 5V /30mA using PWM output and inductor?
    For now I am using TPS60140, but would like to simplify whole thing.
    I know I can use TL2775 and few external components as well

    The goal is to cut the cost for small batch (~25 pcs)

    Point me to the righ direction please.
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  2. 24th February 2008 02:17 PM #2
    blueroomelectronics
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    Yes you could build a boost converter with PWM, there are a few companies making 3.3V LCD displays like www.topwaydisplay.com
    Bill
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  3. 24th February 2008 02:19 PM #3
    Hero999
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    What's the battery voltage?

    You can use a flyback inductor circuit to generate higher voltages but you need some feedback to stop it from rising to too high.

    Does the microcontroller have an ADC pin?

    You might also be able to use the comparator to cut the pulses when it gets to 5.01V and start them when it drops below 4.99V which would give 2mV of ripple.

    I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong.

    Please ask on the open forum if you have a question and I'll be happy to help,     if I know the answer.
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  4. 24th February 2008 02:19 PM #4
    bananasiong
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    How about charge pump with only diodes and caps via one output pin?
    Last edited by bananasiong; 24th February 2008 at 02:25 PM.
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  5. 24th February 2008 02:30 PM #5
    Andy_123
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    @blueroomelectronics:
    I have to use a small display that fits in specific box (16x2 LCD 60mm wide max), if you can point me to a 3.3V display, I can use it

    @Hero999:
    It uses 2xAA batteries, TPS60120 generates 3.3V, TPS60140 generates 5V.
    PIC has available ADC pin, and I am looking if someone already has design
    PWM->inductror -> load-> feedback to ADC

    @bananasiong:
    this will be another option, but I need about 30mA, will it work? Can you point me to a working schematics please.

    Like I said I have TPS60140 with 4 capacitors working, but trying to reduce cost.
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  6. 24th February 2008 02:32 PM #6
    blueroomelectronics
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    This page has 16x2 3V (3.3V) displays.
    http://www.topwaydisplay.com/Product...Char/index.htm
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  7. 24th February 2008 02:36 PM #7
    Andy_123
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    Quote Originally Posted by blueroomelectronics
    This page has 16x2 3V (3.3V) displays.
    http://www.topwaydisplay.com/Product...Char/index.htm
    None of 3V LCDs one this page are less than 60mm wide
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  8. 24th February 2008 02:38 PM #8
    blueroomelectronics
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    What LCD do you have?
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  9. 24th February 2008 02:38 PM #9
    bananasiong
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    What type of LCD you use that consume that much current? I've used one which draw only 3 mA that I can directly power from the PIC.
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  10. 24th February 2008 02:41 PM #10
    Andy_123
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    http://www.hantronix.com/down/16216ls.pdf

    53mm wide

    Should I try to run it from 3.3V?
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  11. 24th February 2008 02:42 PM #11
    bananasiong
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    I mean I was using 5 V. 3.3 V most probably won't work.
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  12. 24th February 2008 02:49 PM #12
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    Just a thought, the ENC28J60 chews through power when the Ethernet is running, the LCD backlight will also burn through power. You power source is only 200ma have you measured it, is it enough?
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  13. 24th February 2008 02:49 PM #13
    Andy_123
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    Right now I have 80 mm LCD in different box, no backlight and it uses few mA only
    Adding backlight makes it power hungry.
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  14. 24th February 2008 03:15 PM #14
    bananasiong
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    Hi,
    I think this is enough for a few mA. Try with a load resistor first.
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  15. 24th February 2008 07:47 PM #15
    Andy_123
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    Quote Originally Posted by blueroomelectronics
    Just a thought, the ENC28J60 chews through power when the Ethernet is running, the LCD backlight will also burn through power. You power source is only 200ma have you measured it, is it enough?
    I am not using ENC28, I am using 18F66J60 and TYP value is 180mA and TPS60120 works just fine - device typically used for just a couple minutes once in a while and TPS can handle short overloads up to 300mA.
    As of today LCD uses own regulator directly from the battery.
    But you are right: adding LCD to 3.3V source may be too much for TPS60120.
    Last edited by Andy_123; 24th February 2008 at 07:50 PM.
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