This is a gift idea so specs are rather tight ....
Vin = 8 - 10V
Vout nom/max= 12 Red Leds ~ 12*2.3V = 28 / 30
Iout nom/max = 11mA / 13mA
Vdiode = 0.3
Pout = ~0.37W

The questions...
- Which old IC can do the job? (if any)
- No old IC? Can i make my own discrete boost converter? Links would be welcome ...
- Ordering off the internet is not an option currently. However suggestions are welcome - since if there is no old IC to do the job then I guess ....

 

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You may want to take a look at National Semi's WEBENCH LED Architect.

http://www.national.com/analog/led?gclid=CIjIyZnDmagCFaNd5QodMmUieg#software

 

You may want to take a look at National Semi's WEBENCH LED Architect.

http://www.national.com/analog/led?gclid=CIjIyZnDmagCFaNd5QodMmUieg#software

Unfortunately, that's not going to help our OP much, as they most likely cannot order those parts.

I don't even know what kind of circuit to suggest, as I have no clue what components might be available to them.

If they can get their hands on a spare PC power supply, they would find at least one switching regulator, and several usable toroids. Beyond that, they'd have to do a lot of reading about the IC(s) they found.

I won't have time to be of help here.

 

Unfortunately, that's not going to help our OP much, as they most likely cannot order those parts.

Ahh!

I completely missed the location.

@themindflayer, what IC(s) were you thinking of using and what do you have available to you?

 

@retched Thanks .... am looking into the software ...

@SgtWookie about availability ... any IC made after 2005 may not be available ... toroids / inductors/ etc will be easily available ....

ST's viper series is available but it is not suitable for battery powered apps ... ICs UC384X, SG3525 etc and ICs used in old TVs etc will be available ... Here traders dont have a list of ICs otherwise searching would be easier ... I will need to go up and say do you have this ...

so if you've used some IC 5 - 10 yrs ago it would probably be available ...

sgtWookie got me thinking .. which appliance should i open up to get a sw reg capable of battery powered op? Cell phones? Laptops?

The application is a battery powered necklace (iron man kind but with a red heart ) and so the specs are this tight ... 12 red leds (not the HB kind) I checked them out at 11mA 2.15V ... increasing current doesnt increase the brightness noticeably .... any other suggestion would be nice ....

Is a discrete solution possible?

Thanks again ...

 

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Discrete solution shouldn´t be that hard.
You need one op-amp for the oscillator, one comparator to get PWM and that´s about it, if you want it regulated you need one more opamp for the feedback.
Use boost topology like here, http://www.smps.us/topologies.html and see where that gets you.

 

If you were truly desperate you might try something like this. A couple of transistors running as a boost converter, with a peak coil current essentially determined by a transistor VBE. My version is driving only 10 LEDs as I do not have any models with the same forward voltage as yours.

I have only simulated this and so can't be sure these little transistors would really survive: you might want to find something with a bigger VCEO for Q2. Note that the coil inductance is not that critical, say about 1mH to 5mH, but it must be able to handle 50mA without saturation. R4 adjusts the drive level.

No proper regulation: the peak current is "set" by VBE, but the charging time and hence the mean output will vary with the supply voltage. This will not be very efficient either, but may be good enough, possibly better than just running the LEDs in shorter strings via resistors.

 

Why connect 12 LEDs in series? So only one current-limiting resistor is used but then a complicated voltage stepup circuit is needed?

Simply connect each LED in series with a current-limiting resistor and power them from a 3V to 6V battery.

Or connect two LEDs in series and in series with a current-limiting resistor to make a string. Then connect 6 of these strings to a 6V to 12V battery.

Or connect three LEDs in series and in series with a current-limiting resistor to make a string. Then connect 4 of these strings to a 9V to 12V battery.

 

Below is a first pass at just such a power supply It supplies 300 ma (or more if you do not adjust it carefully!) to a 1 watt white LED.

The circuit shown is developmental, I only put it together last night and have yet to optimize it.

The current regulation is a function of the battery voltage, mainly because of the poor performance of the zener (will replace with TL431) and the amount of hysteresis through the 100k resistor is a function of battery voltage. The current drifts at about 0.33% per degree C, but this can be compensated by using 1 meter of #38 copper wire for the current sense resistor (I have not gotten this far yet).

This circuit works pretty well as it is at the moment, having been tested from 4.5 to 10 volts. The only thing that gets warm is the inductor's core, and with the particular inductor I am using, it only rises about 25 degrees C over ambient.

 

Thanks everyone ....

@Adjuster looking into your circuit now ...

@Audioguru .... i had arrived at that solution just yesterday!

I remember seeing a similar project at instructables long ago and i was wondering how the hell did they manage to pull it off! and then it struck me!!!

Thanks everyone

 

Thanks DickCappels ... did not see your reply until I posted .... l am looking into it too .... will let you know any updates

 

DickCappels ... i needed a boost converter! Sorry! You can rest easy .... AudioGuru's solution is what i am going to try first ....

Vin = 8 - 10V
Vout nom/max= 12 Red Leds ~ 12*2.3V = 28 / 30
Iout nom/max = 11mA / 13mA
Vdiode = 0.3
Pout = ~0.37W