Flashlight 3xAAA replacement

​I got a flashlight as the first ever kind gesture from my apartment management for the most recent schedule 24+hours maintenance power shutoff. It has a very nice reflector for a square LED and a smaller chip inside that controls the 3 operating modes. 

Off course I had to open it up right away.  It uses 3AAA on the usual battery holders for cheap flashlights.  I smell trouble or an opportunity for some corrective active.  I am not fond of using odd numbers of AAA batteries as I have been using rechargeable since NiCd days.  I don't know if they use a constant current driver, so could be trouble for 3 fully charged NiMH (1.4V x 3 = 4.2V) with low internal resistance.

I used the parts from a 5V booster board I bought from the usual places, but modified the feedback divider for 3V which is just bright enough to drive LED, but low enough to not go into thermal run away.

U1 has the same pin out as the unknown part used on the board.

As my replacement board has 3 contacts - 3V and 2 GND, I had to move the battery off centered to avoid shorting the 3V output to the front of the PCB.  

I used easily soldered and bent metal strips  to form a battery guide and the hinged -ve terminal.  They are used to crimp the end of plastic mesh for store bought onions and garlic.  

My battery terminal help to make better connection between the offset battery and the spring loaded terminal the of the flashlight cap to the right side of the picture below.

It also acts as a pull tab for the PCB assembly when it is time for replacing battery.

Attack of the blinking dimming flashlight

I would never have thought that the blinking dimming light movie tropes is being kept alive by poorly made flashlight clicky switches.

I managed to extract the mechanism that was pressed fitted into the end cap of the flashlight.  They use some iron strips as part of the contact.  There are 2 such contacts in series and they gets even worse as I use the switch for the boost supply with about 3X currents.

I cut2 pieces of gold plated (15um) pin from a 2mm connector.

I soldered them onto the contacts.  The contacts needed to be bent flat as the pins adds extra thickness.

There is a metal piece that looks like a top in the previous picture.  I had to bent the circular part down to make more clearance for the pins. I reassembled the switch and soldered a short piece of bare stranded wires.  This wire helps to make better contact to the side wall of the end cap.

Unfortunately the plastic they used is too soft and I do not have the right jig to press it back in place.  If there were a time I wish I had a 3D printer, this would be it.

Anyways this fix got rid of the flimsy flickers and the light a lot brighter.

DIY Amplifier collection

Here are some of my DIY amplifier collections:

I built one of these back in my school days out of a pair of TI/National Semiconductor's Class A-B LM1875 20-W Audio Power Amplifier. Build straight out of their application circuits. I mounted in 2 of these amplifier into a 60W heatsink.

I recapped, cleaned up the layout and mounted it with a Transformer (33V CT 1A), rectifiers (200V/3A) and filter caps (1000uF x 4) onto a piece of board from a clementine box.  It served as my TV/Computer amplifier for about a year.

It was from the days of good old analog design with honest specs.  Note their 20W is at the lowest THD.  

They have excellent PSSR (Power Supply Rejection Ratio) around 95dB at 120Hz.  I can simply run it off a full wave rectifier from a transformer.  They aren't too efficient, so my choice of 60W heatsink was appropriate for continuous operation of 2 amplifier at full power.

I later built a few of the 60W module out of a pair of TI/National Semiconductor LM3886 68W Class-AB amplifier.  (I didn't have a LC meter, so the inductance value on that coil as way too low.)

Sadly at that point I gave into craze and bought myself a  surround sound receiver. I sworn to rip out and replace the "discrete" amplifier at the expiration date of the warranty, but didn't follow through.

They are probably one of the better if not the best chip amplifier that a lot of the DIY amplifiers designs are based on.

However you would want to use 4ohms speakers to take advantage for the full rated power at low distortion.  

Recently, I started playing around with those Class D modules from China to connect to my computer surround sound analog output.  I tried the $0.30 PAM8403 modules but there was a lot of noise for my rear speaker probably due to the parasitic of the longer cables.  I went for the PAM8610 "10W" modules.  The first one was bad as it took too much design freedom.  

I then read the reviews and moved on to the "better" version of the module that did follow the reference design. I wish they break out the volume control and the balanced input.

I mounted 3 of those modules onto a extruded heatsink from an old monitor.  The heatsink is probably good for up to 10W. I covered area on the bare aluminium heatsink  with "Kapton" tape where I have wire connections.  I used pieces of thermal conductive tape on the thermal vias under the chip to carry heat to the heat sink.  The heatsink tape I used was electrically conductive, so the heatsink and the metal case was grounded because of that.

I ran a power bus with a 1000uF electrolytic cap and a few 1uF ceramic caps near each of the power input of the amplifier blocks.  There is a ferrite bead for each amplifiers to block the high frequency noise injecting back to the VCC bus rail. I didn't have the same layout for the amplifier at the bottom and it was a bit noisier.  The layout in the picture below fixed that.

The heatsink was mounted at the opposite to the messy wiring which helps a bit to balance the drag from the wires.

Here is why i used air quotes on "10W" as I am using a 9V supply, so I would be happy to get 5W out of mine.

The PSRR isn't as good as my other amplifiers.  I actually can hear 60Hz hums using AC transform + rectifier.  I ended up using a good quality 9V 40W brick, so 5W per channel was the best I can hope for anyway.

Either I have insanely good ears for the hiss or the -90dB isn't quite feasible without a lot of work.  I can't hear any noise from my 20W Class A-B.

It is not a perfect set up, but it is good enough for me for now.