IC boost converter the next generation

Projects /  LED  Original Posted date: 07/18/2018

It all began last summer when I picked up a flashlight in the local thrift store.  I thought it would work nicely with AP3019 LED driver.  It turns out that the part has a minimum voltage of 2.5V which kinda kills it for 2 AA NiMH.  I have no choice but to try out my $0.10 MT3608 boost converter (.pdf).

It has a reference voltage of 0.6V which is a bit high for making a constant current.  I have decided to drive the LED at a fixed voltage of 3V which I have been doing for the other flash light for the last 3+ years.

The measured voltage is 2.93V which is -2.3% from the mark.  The power consumption is 200mA at 2.4V input.  It loses regulation at 2.1V and works down to ~1.75V.

The recommended 22UF for the input and output caps.  I only have space for 0603 parts so 1uF is probably large enough for a 1.2MHz supply.  This application doesn't see much of fast load variations to need bigger values.

Here is the layout.  I have broken easily a dozen DRC rules etc.  I have 8 home made vias to help thermal dissipation.  They are small pieces of AWG24 bare copper wires (slightly oversized) inserted into the 0.5mm holes.  I trim the ends with a pair of diagonal cutters and hammer the copper wire flat before soldering.

Here is what it looks in real life.  The colar in the middle is a left over part from my other modded flashlight.  It has the same diameter and  thread size too.  All the components and traces must fit within the hollow space.  The collar is grounded and make contact with the ground fill on the outside part of the PCB.

The positive terminal makes contact with the PCB via a spring.  The PCB is pressed against the collar which make contact with the case.  I might make a ring out of gold plated header pins in the future if this connection proves to be unreliable.

This is how the assembly would fit.  I put a piece of kapton tape over the LED supply trace for insulation.  I used JB Weld to hold the PCB and collar together.  JB Weld is a high temperature epoxy reinforced with some steel particles which also helps the thermal properties.  It was actually used as a heatsink adhesive by early PC overclock enthusiasts. I bake it at 95C (200F) for 20 minutes to harden it (because I am inpatient.)

Next step is to modify the lens assembly.  The LED is roughly the same height as the filament in the old bulb.  I'll need to make a bigger hole to accommodate the wider LED package.

I have no idea how to take apart the lens and reflector.  I got a bit impatient and used a milling bit to work on the aluminized plastic reflector.  I have to file the LED PCB because it was too big.

I didn't do a good job centering the hole.  I have to live with that.  I cleaned up the hole bu hand turning a grinding stone provided in my Dremel kit.

Wide beam vs spot on wall - same distance.  My other flashlight no longer have a beam adjustment as I needed the on/off switch more.

My two flashlights modded with LED.

New vs old:

Old one draws 160mA (2/3 power of new ) and survive the average power outage here on old set of NiMH.  I like my new toy, but I would keep the old one around.

New LED is cheaper at QTY 10 for $0.67 -  $0.067 each is less than what I pay for regular 3mm LED locally.  Even for fake Cree, I think it is great.  Cheap ($0.10) high efficiency boost converter and working beam adjustment.  Old one doesn't have beam adjustment and brightness probably degrades over time.  :(

Files are available: my github