It's hard to find a good D-cell rechargable battery.
The Ni-MH D-cell from Energizer is a big tin can with a little AA cell inside. They must be using awfully big wires in there because its internal resistance is only 11 milli-ohms. :lol:
I tried my NIMH batteries with the circuit, and the only noticable change was it got dimmer.
Something is turning on Q1 way too hard because its shorting VCC to ground. It should only be on to charge of L1, then turn off. Instead it is always on. I really want this circuit to work, but im so frustrated with it!
I guess I'll re-order the parts from farnell, and mount the SMT stuff on little circuitboards with wires so that I can experiment with this circuit on my breadboard.
Hi Zach,
I am sorry that changing the battery type didn't fix it.
I think the project's frequency would be too high and its output voltage would be too low (your syptoms?) if the value of the coil's and power transistor's 33milliohm current sensing resistor is too high.
How is its value marked?
How would you measure it?
I think ive finally got the bloody thing working!!
It is EXTREMELY bright with two regular AA batteries whose series voltage is only 1.35V!!
I ordered more of the SMT chips and transistors, made a PCB so that I could put them on my breadboard and fiddled around with it. I still don't know what was wrong with my PCB version.
I have one question though: This circuit is pulling 1.3A from those batteries. Only 100mA is going through the LED. Here's the weird thing: Around 1A is going through Q1and its getting very hot. Fortunately Q1 is rated at 4A.
Does this sound like a normal thing for a DC-DC converter or is there something wrong?
Hi Zach,
Yeah, something's wrong. Its efficiency is only about 20% when it should be better than 80%.
You have 1.35V at 1.3A from the battery which is 1.76W.
The LED is about 3.5V at only 100mA which is 0.35W.
0.35/1.76 = 20%. Therefore 80% of the battery's power is heating the circuit.
Hi Zach,
I'm stumped too unless you used a slow ordinary rectifier instead of the spec'd extremely fast-switching Schottky diode.
Also, if the core of the inductor saturates then it will act like just a piece of wire.
Hey audio, its definenately neither of those: The diode is one specified by the schematic, and the inductor is rated @ 3 amps, so its not saturating.
I havent got the chance to fiddle with it some more since i sort of got it working. I just got a digital camera so ill be able to post pics of the finished product when its done.
How many uH is your inductor?
If your inductor does not store enough energy, it may be trying to draw more current by leaving it on longer, yet the battery may peak out in the number of amps it will provide. It gets hot, sucks a lot of power, but little output.
You need an oscilloscope here, you can't get answers without it. For one, you need the current and voltage waveforms off the battery. Just the average that a multimeter gives won't help much.
I bought inductors for speaker cross-over networks from a high-end speaker manufacturer. They sounded bad. I measured them and their inductance was incorrect.
So I took my real-time-analyser into the manufacturer's showroom, played pink noise into their very expensive speakers and showed them the hole in the response cause by their incorrect inductors.
The high-end speaker manufacturer's quality control department cared so much about the appearance of their speakers that they didn't even measure them, maybe not even listen to them.
Zach, maybe the manufacturer of your inductor "hopes " it is 22uH and can pass 3A. :roll:
I GOT IT WORKING!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! AFTER A MONTH OF TINKERING WITH THIS STUPID CIRCUIT I GOT IT WORKING!!!!!!!!!!!!!!!!!!! :lol:
I breadboarded it and fiddled around with it and somehow got it working, even though it is exactly the same as on the PCB. How or why it is working now is totally beyond me! Now I just have to make a PCB for it. I just got a digital camera so I thought i'd take some pics :lol:
Nice work, i've been following this thread because i'm interested, but haven't made any posts because I don't even know how it works :lol: . I suppose you'll want to be putting it into some sort of torch body now?
Hi Dr. EM,
Its DC to DC converter works by its oscillator driving a power transistor to conduct a high current in an inductor. Then it quickly stops the inductor's current and it develops an inductive voltage spike as its magnetic field collapses. The voltage spike charges the circuit's output capacitor to a voltage higher than the supply voltage. The IC senses the output voltage and regulates it as the battery voltage drops over its life. :lol:
Yes, Im going to mount it in a torch now. I'm thinking about buying a 3 D-cell maglite and putting it in there. First I'm going to try it with my 2 D-cell maglite.
In the 3 D-cell maglite, if I put two batteries in parallel, and one in series with those two parallel, ill still have 3 volts right? This would extend the life of the flashlight considerably. Not only that, but ill have a very advanced flashlight that can also be used as a blunt object weapon :lol:
Im gonna start on the PCB in eagle right now. Ill make sure to post more pics of the finished product, and the beam that itll be able to throw with a reflector.
Hi Zach,
If you have one battery cell in series with others then it will fail just as quickly as if the others weren't in parallel. When it is discharged then it is a high resistance and the circuit won't work.
Fabricate a dummy cell for the 3rd one. :lol:
R1 would likely cause problems the way you have it mounted on the board. 33mOhm is pretty low and the contact resistance of the board is probably higher than that, inconsistent too.
R1 would likely cause problems the way you have it mounted on the board. 33mOhm is pretty low and the contact resistance of the board is probably higher than that, inconsistent too.
Hi Zach,
If you have one battery cell in series with others then it will fail just as quickly as if the others weren't in parallel. When it is discharged then it is a high resistance and the circuit won't work.
Fabricate a dummy cell for the 3rd one. :lol:
R1 would likely cause problems the way you have it mounted on the board. 33mOhm is pretty low and the contact resistance of the board is probably higher than that, inconsistent too.