16 volts 3A regulated power supply help

[sunny]

I have electronic key board and it requires 16volts 2.5 A regulated power supply.Now i'm having 230 volts 12-0-12 ,5Amperes Transformer.So please help me how i can construct 16 volts 3 A regulated power supply using 12-0-12 volts Transformer.
Any help is highly appreciated.

Thanks,
SUNNY

[pinkmouse]

Hi Sunny

Google the LM317 datasheet, that contains all the info you need. Get the TO3 can version so you can mount it on a decent heatsink and, ignore the centre tap of the traffo so you feed it with 24V.

[moamps]

Hi:

The maximum current of the LM317 is 1.5A, which is not enough. The LM338 might be a better choice. Anyways, I think that in this particular case it would be better to use a switching-type regulator (due to power dissipation issues associated with linear regulators such as the LM338). Best yet would be to buy a suitable switching power adapter used for notebooks.

Regards,
Milan

[AndrewT]

Hi Sunny,
the 12Vac will give about 17Vdc after the rectifier and smoothing caps.
This is too low to drive a regulator and get 16Vdc output.

Series connecting the 12+12 will give 34Vdc. This is way over Pink's estimate of 24Vdc.

The regulator will have to lose 18V to get down to your 16Vdc.

At 2.5A continuous the regulator will have to dissipate 2.5 times 18 = 45W. This will need an enormous passive sink or a big fan cooled sink.

Does your supply need to be regulated?

What if you fed the 17Vdc from the smoothed PSU straight into your circuit? After the rectifier the voltage will be about 16Vdc when fully loaded to 120W.

A slight problem may be the regulation of your transformer. The open circuit voltage will be higher than 12Vac and the rectified DC will also be higher until you load the transformer.
You could have 18.5Vdc if the regulation is 10%. Take off your diode drop and you may have about 17 to 17.5Vdc before you load up the transformer.

[pinkmouse]

That'll teach me to post before the second mug of tea! Sunny, ignore everything I said!

[AndrewT]

Hi Pink,
I need the extra caffeine in coffee to wake me up and talk sense.
Even though I am aware of the codswallop that comes out of my fingers first thing in the morning I still insist on breaking my own rules.

[Nordic]

With less than 12V differential the LM317 is closer to 2.5A Rateing

but you could look at using LM350 in its place which almost doubles it's rateing, and can give you about 2.5A at a 15V DIFFERENTIAL.

[edl]

Hi,

an LM2576-ADJ will easly do it...

Regards,

On the margin, you can use TOP244/249, then there is no need for that mains trafo.

Or let's buy a cheap, used notebook power supply. They are just somewhere 16V/2.5A...

[BWRX]

How clean does the regulated voltage have to be? Why does everyone always overlook the very simple but effective emitter follower with a zener reference? To get the 16V output you can put a regular diode in series with a 16V zener to get about 16.5-16.7V at the base of the NPN transistor. Alternatively, you could use the base-emitter junction of another transistor of the same type that is used as the pass element as the diode in series with the zener to get a more closely matched voltage.

[sunny]

Hi Friends,
Thanks for our replies and my keyboard requires 2.5 Amps only and i'll be very grateful if someone give me the circuit diagram of 16volts regulated power supply using the existing 12-0-12v transformer.
Waiting for your replies.

Thanks,
SUNNY.