Boost Converter Vout Drops a Lot with Load

[bumba000]

Why does the Vout get so low when attaching a load to boost converter?

Attach battery and Vout is 3.61
Attach 1.5ohm load and Vout goes down to 3.1
PWM at just about any hz or Khz and Vout goes down more as far as 2.2.
Without the load, Vout can go as high as 20v or so.

https://www.digikey.com/product-detail/en/IRLR6225TRPBF/IRLR6225TRPBFCT-ND/2538170
https://www.digikey.com/product-detail/en/SRP1770TA-2R2M/SRP1770TA-2R2MCT-ND/5429726
https://www.digikey.com/product-detail/en/RR71C101MDN1/493-3716-ND/2207252
https://www.digikey.com/product-detail/en/VB20100S-E3/8W/VB20100S-E3/8WGICT-ND/1543677

[tron9000]

Wattage,

The best way I can describe it is wattage. Say the output is specified to 1W - you can draw 1V @1A, or 2V @ 0.5A, or 0.5V at 2A.

so in your case you output of that boost converter P= V²/R

Good to see you back.

I'm assuming that the parts you have linked are the parts you have used to build a converter? (last link is 404 BTW)

[bumba000]

yes they are the parts I've used. They are much "beefier" than those in a typical store bought circuit that does the same thing. Honestly I may have just found the issue. I have the voltage going up now when the load is attached. The lead from mosfet drain I had to diode anode, from anode to junction of inductor an caps. Instead of drain to junction of inductor and anode. As soon as imgur.com lets me upload images, i'll show what I mean.

I appreciate your response and don't want you think I bailed out so I'm responding now without the schematics.

Thank You, John

[bumba000]

So sorry to bother you with my mistake. Thanks again for taking the time. Your response is much appreciated.

[tron9000]

<sucks teeth>

there's alot wrong with those designs, but I think I can see what your trying to do.

The correction you made is right, however the way your supplying power to  the boost converter is a bit scary.

The 18650 cell: I'm assuming that you wish to charge it off the Trinket 3V supply? if so that isn't really the way to do it. You can buy little Li-ion charger units to do this.

Using the Trinket 3V supply: as a safety measure I would put a beefy schottky diode between the 3V and the battery

[bumba000]

I'm powering the converter from the battery. I'm powering the trinket from the battery. I have "lipoly backpacks" for charging the battery from the trinket. Just got some fuel gauges in the mail too. Just didn't show all that in the schematics.

At first I had planned on building my own "lipoly backpacks" but for just about 4 dollars each vs 2 dollars each for parts and soldering it all up myself?? It's worth the extra cash.

[tron9000]

ahh right, well you would benefit from a buck/boost converter from the battery to power the trinket as batteries don't supply a constant voltage and you may find your trinket will object to too high voltage input or may drop out earlier than expected.

something like this:
http://www.gearbest.com/development-boards/pp_69338.html?currency=GBP&gclid=Cj0KEQjw75yxBRD78uqEnuG-5vcBEiQAQbaxSO8C_R1ZnG8ODHy3VHjEJYLuysBB8X9L6RJWvanuhcUaAmM78P8HAQ

[tec5c]

I thought you had the project finished and were using it? 

[tron9000]

now you mention it tec5c - I'd love to see some photo's of the progress bumba00.

you don't have to, but I've seen some guys a while back who had built there own version of vapers and they looked quite cool - even though I don't vape (I much prefer the cheeky Cuban once a blue moon)