3V to 9V converter

[Dr.james]

Great bounty and ronv, i appreciate your reply, looks like the Lm3721 is gud idea, but i don't know whether it's obsolete or will be available here

 

[Electroenthusiast]

@ziddik/anyone, you dint reply to my legitimate question: #34

Why not use a 9V battery? When you can get them easily?

 

[bountyhunter]

Great bounty and ronv, i appreciate your reply, looks like the Lm3721 is gud idea, but i don't know whether it's obsolete or will be available here

Doubt the LM2731 is obsolete. I think we brought it out around 2007. It was making a TON of money doing the LED backlight apps for PDA devices. I'll bet Digi-key has it.

 

[Dr.james]

Sorry guys, it is not available here. I searched for it in a number of shops but they all say it is obsolete. So are there any simple circuits using transistors? I have some 13001,mje13005a transistors in stock

 

[Dr.james]

@ziddik/anyone, you dint reply to my legitimate question: #34

9V battery will drain quickly if i used it for a Tx, that is why

 

[Electroenthusiast]

9V battery will drain quickly if i used it for a Tx, that is why

Hi James,
Ok, this was bothering my mind for sometime, ty for answer.
Do you mean it because they have low mAh rating.

 

[audioguru]

Digikey has 46,783 LM2731 ICs in stock for $2.00US each.
Farnell is in many countries and have 2801 of them in Australia ( https://au.element14.com ) for $3.12AUS each.

I did not look for X or Y versions so look yourself.

 

[audioguru]

Do you mean it because they have low mAh rating?

Yes.
Look at the datasheet of a 9V alkaline battery on the website of its manufacturer. It lasts long if its load is only a few mA.

My FM transmitter draws 53mA and after 2.5 hours the brand new 9V alkaline battery is down to only 7V and the range of nthe transmitter is reduced a lot.

 

[Electroenthusiast]

Yes.
Look at the datasheet of a 9V alkaline battery on the website of its manufacturer. It lasts long if its load is only a few mA.

My FM transmitter draws 53mA and after 2.5 hours the brand new 9V alkaline battery is down to only 7V and the range of nthe transmitter is reduced a lot.

That answers my ques. I would also suggest to use a series combination of 3V(or 3.7V in above case) to get 9V. That would also work, but perhaps we need to again use a 7809 to get a stable 9V output.

 

[audioguru]

A 9V alkaline battery has six tiny AAAA cells in series.
A tiny AAAA cell has a capacity at low currents of 600mAh but an AA cell has much more capacity of 2800mAh (4.7 times more) at higher currents.
A 9V alkaline battery weighs 45.6 grams and six AA cells weigh 138 grams (3 times more).

 

[Dr.james]

Digikey shows that they are unable to supply only a single lm2731 they want me to buy atleast 100 Pcs. hell no!!

 

[audioguru]

https://au.element14.com/ has a warehouse full of the IC in Australia but Digikey does not have a warehouse there.
Won't https://au.element14.com/ sell you one?

 

[Dr.james]

No.heck, sometimes i start hating this country

 

[bountyhunter]

No.heck, sometimes i start hating this country

You might try calling National Semiconductor directly, ask for the Applications group for Power management. They had an 800 number. Here is the secret:

Call them up and make up a fake name of your "company", like Power Convergence Systems. Tell them you are developing a boost circuit and you need a few samples of the LM2731. I used to send parts out all the time for free.

 

[bountyhunter]

That answers my ques. I would also suggest to use a series combination of 3V(or 3.7V in above case) to get 9V. That would also work, but perhaps we need to again use a 7809 to get a stable 9V output.

I would use three Lithium cells in series. I believe the Li MnO2 (lithium manganese dioxide) types have a full (new) voltage of 3.3V. I doubt you need to use a 9V regulator.

 

[Dr.james]

Please post a schematic using transistors! Isn't it possible?

 

[audioguru]

No.heck, sometimes i start hating this country

A few years ago, in your country, Silicon Chip magazine published three 1.5V then 3V to 9V converter projects using ICs from Texas Instruments. One converter IC is the TL499.
Look in Google for: Never Buy Another 9V Battery.

 

[Dr.james]

u r talking about obsolete parts audioguru. and the colin never helped me but staying away even though he can help me on this project, Nice ozzies!

 

[ronv]

Can you get any common ics or does it have to be all transistors?

 

[colin55]

You have not made it clear what transmitter circuit you are using.