DC-DC converter circuit for 1 AA cell (low power)

[snovotill]

The flyback circuit below has improved efficiency because:
1) Feedback winding does not load the core during flyback
2) The 4.7nF capacitor increases transistor turnoff speed
3) 1:1 Turns ratio reverse biases E-B junction at turnoff

More Circuit info

The circuit does suffer from losses at the current sense resistor, though that could be improved by adding a current mirror or by putting a couple of LEDs in series.

 

[paulr]

Re: DC-DC converter circuit for 1 AA cell (low pow

Can you get rid of more of the junction losses by using mosfets on the low voltage side?

 

[snovotill]

I've just succeeded in driving One Hundred (100) red LEDs all in series at 12mA, from a small photoflash circuit out of a disposable camera, operating on a 1.5 volt battery. I had to upgrade the transistor because the original one was getting really hot and did not have a low enough on resistance. The LEDs went accross the big HV capacitor, but I made shure it was discharged prior to hooking the LEDs up! The transformer losses were quite high because the secondary has wire as fine as peach fuzz. The AA battery went flat real quick!

 

[paulr]

Re: DC-DC converter circuit for 1 AA cell (low pow

Wow, what a "shocking" story! /ubbthreads/images/graemlins/grin.gif

 

[paulr]

Re: DC-DC converter circuit for 1 AA cell (low pow

By the way, welcome to CPF!

 

[snovotill]

Hmm, the mosfet needs a few volts to turn on so that would be even worse if I understand what you mean. A simple current mirror should work, but who needs all those extra parts. Someone should try putting more LEDs in series and extending the winding to form an autotransformer?

 

[snovotill]

Here is the more efficient version of the circuit using a current mirror to reduce LED current sense losses:
Unlike the other circuit, this circuit is untested.

and the description again

http://members.shaw.ca/novotill/LedSupplyRegAA.TXT

 

[LED_ASAP]

[ QUOTE ]
snovotill said:
I've just succeeded in driving One Hundred (100) red LEDs all in series at 12mA, from a small photoflash circuit out of a disposable camera, operating on a 1.5 volt battery.

[/ QUOTE ]

100 Nichias generate >300V. At 12mA that is 3.6W! If you consider the efficiency loss on the transistor and transformer, that means >5W from the battery. No wonder the battery gets flat in no time and both the transistor and the transformer get hot!

If you managed to get 3.6W out of a single battery, maybe it would possible to re-wind a transformer that delivers 3W to a 5W LS from a single AA battery, too /ubbthreads/images/graemlins/blush.gif

 

[MrAl]

Hello there,

I've used higher turns ratios to get higher output
voltages. The drawback is that the efficiency goes
down with the step up transformers, although it
does work.

Good luck with your LED circuits,
Al

 

[snovotill]

The simple boost circuit at the top of this thread will also run nicely off 3VDC if you reduce the 1nF capacitor to 470pF and increase the 470 ohm resistor to 1.5K or so.