120 to 16 volt power adapter

[Jwitty]

Hey guys. New to the forum. I’m currently doing a project in my tech class where we could choose a circuit and build it. I am building a trickle charger for automotive 12 volt batteries and I’m done with the circuit but need an adapter to go from 120ac to 16v dc at around 1 amp. I can’t find any reasonably priced transformers. Anyone have a solution? Thanks in advance!

 

[MaxHeadRoom78]

There are Wall-Warts galore that will do it, very cheap!
Max.

 

[Jwitty]

There are Wall-Warts galore that will do it, very cheap!
Max.

If I could get them for <5 bucks I’d go that route. Cheapest I can find are 15 and trying to make this project as cheap as possible.

 

[MaxHeadRoom78]

If you already have any on hand for lap tops etc, and they are higher voltage, just build a simple regulator. (LM317 etc).
Do you need it regulated?
Max.

 

[Diver300]

**broken link removed**has some at that sort of price

 

[audioguru]

Cheap means poor quality and short lifetime.

 

[Jwitty]

If you already have any on hand for lap tops etc, and they are higher voltage, just build a simple regulator. (LM317 etc).
Do you need it regulated?
Max.

The circuit is running an lm317 to regulate to 13.25 volts with a zener diode after to act as a max voltage cutoff.

 

[Jwitty]

**broken link removed**has some at that sort of price

Found a lot of cheap 15 volt ones. None that are 16 though.

 

[Jwitty]

Just wondering if I could use a buck converter that could take 120 volts down to the 16 volts I need and 1 amp?

 

[Externet]

A discarded/borrowed laptop power supply / charger usually provides ~19 VDC, can be found at pawn/recycle/junk/computer/used stuff places; and your LM317 will be happy with it.

 

[Jwitty]

A discarded/borrowed laptop power supply / charger usually provides ~19 VDC, can be found at pawn/recycle/junk/computer/used stuff places; and your LM317 will be happy with it.

It needs to be 16 volts. Any lower and it won’t reach targeted value. Any higher and watts skyrocket as well as voltage. Is there a voltage regulator like the lm317 that has a lower voltage input-voltage output value? If I remember right the lm317 is ~3v

 

[Pommie]

Have you got a good heatsink on the LM317?

Mike.

 

[Beau Schwabe]

"Have you got a good heatsink on the LM317? " - No kidding !!

If there wasn't a concern for galvanic isolation, I would almost lean towards a gated regulator. When the AC is below a certain threshold voltage a transistor allows the full mains to enter, anything above is blocked. Sorry, I don't know the correct terminology for this type of regulator, but I have designed and tested such a regulator from 24VAC to 290VAC input with a variac transformer and it worked great for the application. With a rectified sine wave the output voltage looks like an "M" on a scope where the peak of the M is at the Zener voltage and the bottom of the M is 0V.

 

[Diver300]

If you use a low dropout regulator instead of an LM317 you could use a 14 or 15 V supply to charge to 13.25 V. The reduced voltage drop would meant it would need to dissipate less heat.

 

[jack0987]

Look at this: Meanwell IRM-03 12V
I think they also have a 15 volt version.

 

[Jwitty]

If you use a low dropout regulator instead of an LM317 you could use a 14 or 15 V supply to charge to 13.25 V. The reduced voltage drop would meant it would need to dissipate less heat.

What regulator would do this?

 

[Diver300]

https://uk.farnell.com/texas-instruments/lm2941t-nopb/ic-reg-ldo-adj-1a-to220/dp/3007547

The data sheet is at https://www.ti.com/lit/ds/snvs770i/snvs770i.pdf

That will only need a 14.25 V supply to give 13.25 V. It might manage with a 14 V supply.

It is designed as a voltage regulator but it can be adapted to be a current regulator as well. If the feedback input is raised higher than 1.275 V, the output turns off, so if some current feedback is arranged to affect the feedback input, the current can be limited.