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I need to voltage boost my battery voltage 3V to 12V DC to power cheap RF module transmitter. The boost voltage will last until I transmit 3 or 4 bytes of serial data. Roughly 5ms time.

I read this wonderful article by olin lathrop & trying to understand it.

I need 3V to boost upto 12V. 50mA current is more than enough. Supply battery is CR123 3V Cell.

I have some questions...!

1) Where is the boosted output voltage calculation? How to calculate it?

2) What component values need to change in the attached diagram to get 12V/50mA?

schematic

simulate this circuit – Schematic created using CircuitLab

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    \$\begingroup\$ Back when boost converters were much harder to get and use (and because I'm only a hobbyist, anyway), I used a similar technique (not your schematic, though) to generate the +13.5 V I needed for programming PIC chips. (Many still have an HV programming mode.) This was NOT done open loop, though, as I used an ADC to monitor the voltage. Also, I would recharge (top off) the voltage level after each byte's programming cycle was complete. Given your modest use, you could attempt this. But I think you do need to close the loop. Do you have an ADC? Also, this isn't a schematic I'd use. Needs change. \$\endgroup\$
    – jonk
    Commented Nov 20, 2017 at 7:43
  • \$\begingroup\$ Boosting 3V to 12V in order to get RF supply might not be the best idea. You'll want that supply to be as free from noise as possible. Common practice is to use LDOs for RF supply. \$\endgroup\$
    – Lundin
    Commented Nov 20, 2017 at 7:58
  • \$\begingroup\$ Hi Jonk...Yes I have ADC as well.Do you have a schematic..? \$\endgroup\$
    – Joseph143
    Commented Nov 20, 2017 at 8:34

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The schematics you see is a basic PWM controlled boost converter, with no feedback loop: this is extremely dangerous. The 12V at the output is not guaranteed.

The math behind how you calculate these values is fairly complex. See: https://en.wikipedia.org/wiki/Boost_converter or this paper by TI: http://www.ti.com/lit/an/slva372c/slva372c.pdf Where the switch is your PWM controlled transistor opening and closing at a very high frequency.

As a result, no one designs raw boost converters like that. You should use a dedicated boost converter IC. There are seriously TONS of them. Texas Instruments (again -- no I don't have anything to do with them...) has a fairly good selection of them.

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  • \$\begingroup\$ HI, Actually I want to boost it when I want & not continuously.The output 12V does not need exact 12V, I just want to increase my RF transmitter distance. 3V seems to be very close distance, but when I supply those RF modules from a 12V then the distance can be increased.I need a descrete solution like above. Dedicated chips I cannot find in my area. \$\endgroup\$
    – Joseph143
    Commented Nov 20, 2017 at 6:58
  • \$\begingroup\$ @Joseph143 DigiKey ships to all over the world. Buy a boost IC. Listen to Tony, you will end up severally over and undershooting your 12 V target depending on load and destroy something. \$\endgroup\$
    – winny
    Commented Nov 20, 2017 at 7:04
  • \$\begingroup\$ Agree with all of the above. Just wanted to add that if you do want to try and save power, a lot of these have an enable or power-down line, but definitely watch your transients at that 12V. Lots of decoupling + smoothing probably needed. digikey.com/products/en/integrated-circuits-ics/… \$\endgroup\$
    – ahogen
    Commented Nov 21, 2017 at 1:23

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