19v adapter to 16v?

[spleenharvester]

Is there any way to reduce a 19v 4.74A laptop adapter to 16v using a resistor in line?

The jack is externally attached to the laptop via wires so it would be easy to add on VIN.

Cheers

[mariushm]

Re: 19v adapter to 16v?

I would not recommend a resistor in series... it's kinda hard to heatsink it.

At 4.74a, there's going to be 4.74 x (19-16) = 14 watts to dissipate.

It would be safer to get a LT1083 (5A linear regulator) that you can screw on a heatsink but you'd still dissipate 15 watts.

http://www.digikey.com/product-detai...3PBF-ND/891835

It would make more sense to open up whatever power supply you buy and try to adjust the output voltage by adjusting the feedback going to the controller.

otherwise, the laptop should be a bit tolerant regarding the input voltage so it may be safe to give it 16.5v or more but don't take my word for it.

[spleenharvester]

Re: 19v adapter to 16v?

Hmm, guess I might just be best off to get a cheap used IBM 16v adapter.

It's to power a dead laptop motherboard though that I'm hoping to repair, it wouldn't draw much current right?

Cheers man!

[domas]

Re: 19v adapter to 16v?

well it not common for power bricks to be 16V around me.. I have only seen 19V bricks. But if it is the case, you can try running it of any other p/s (if it is 2 wire design without digital cable).
I agree on what mariushm said, but for long term usage i would prefer switching regulators. They require a few more parts but.. they are more efficient, and they don't have to dissipate a buttload of heat.

I have and adjustable atx p/s lying around, and i can crank it up to 16v, so that is what i would use. But as you already asked I assume that you dont have one.

[Behemot]

Re: 19v adapter to 16v?

Why you want to reduce the voltage?

[bflo60]

Re: 19v adapter to 16v?

hey everyone, I replaced the inverter on my 52" led Philips tv because it had sound but no picture. it worked for a week and now it is doing the same thing again. it has also had a problem for about 3 yrs when you first turn it on there is no sound or picture, but if I unplug the power cord and replug it in it turns on any suggestions? thanks in advance

[Behemot]

Re: 19v adapter to 16v?

Make new thread in the right section.

[ben7]

Re: 19v adapter to 16v?

Spleenharvester, take the adapter apart. Some pics will help. Look for a part that has "431" written on it. These are commonly used in smps feedback circuits. They are adjustable voltage shunts. The voltage is set by two external resistors. To change the output voltage, you simply change the resistors to the right values.

I did this recently - I changed a 12v adapter into a 5v one for charging a USB device

[Behemot]

Re: 19v adapter to 16v?

There is no need to drop voltage to 16 V in the first place. Not a single one. Why adding him work?

[ben7]

Re: 19v adapter to 16v?

There is no need to drop voltage to 16 V in the first place. Not a single one. Why adding him work?

Huh?

1. The O/P DOES need 16v instead of 19v.
2. I'm not adding work. Ye can't get something for nothing!
3. It is obvious that a resistor for dropping the voltage is a bad choice:
A. The resistor needs to dissipate 14 watts of heat
B. The output voltage will not be the same during all loads. At light load it will
be over 16v, which might not be good for the computer at all!!!
4. Mariushm has got the point.

[spleenharvester]

Re: 19v adapter to 16v?

Huh?

1. The O/P DOES need 16v instead of 19v.
2. I'm not adding work. Ye can't get something for nothing!
3. It is obvious that a resistor for dropping the voltage is a bad choice:
A. The resistor needs to dissipate 14 watts of heat
B. The output voltage will not be the same during all loads. At light load it will
be over 16v, which might not be good for the computer at all!!!
4. Mariushm has got the point.

^This basically lol. It's a cheap 16v dead board I bought and I don't fancy buying a fresh adapter to fix it. I only have a 19v adapter.

Can't take the adapter apart cause it's the one I use with my laptop unfortunately!

I might just buy a cheap IBM adapter, I could do with a 16v one because I have a few spare laptops that need to be checked as working.

Cheers

[shovenose]

Re: 19v adapter to 16v?

There is no need to drop voltage to 16 V in the first place. Not a single one. Why adding him work?

lol the reading comprehension fail in this thread is hilarious.

[Behemot]

Re: 19v adapter to 16v?

lol the reading comprehension fail in this thread is hilarious.

I have never seen a device which operates at 16 V exactly, or 14 V exactly and so on. I am not saying they don't exist, but they are so uncommon it is safe to say it will work with voltage from 12 to 25 V. Some of the blodoy Microtec routerboards can even eat 12-42 V *officialy*.

Because 99 % of devices with such voltage have plenty DC-DC modules inside and do not run any single thing inside on the input directly. And because there are always transistors for at least 30 V inside (if it uses 16-20 V input), you can feed it with more or less anything over say 10 V (usually for example in laptops, lowest functional voltage is 5 V).

So instead of asking what does he need it for for first to discover if he by any miracle is the 1 % and if he will actually need to do any modification, you jump to wild theories how to drop the voltage directly?

You know I also asked this question here on forums quite some time ago…I learned something like „it should be safe most of the times“ (actually the 30V FET idea told me soebmody here) and since discovered it is safe almost EVERY time. Ppl do the common mistake of believing the marking on the device even though 8 out 10 times e. g. routers manufacturers do not even supply adapters which are compliant with the router markings!!

[LDSisHere]

Re: 19v adapter to 16v?

Behemot makes a good point. The "safe" way is to find or modify an adapter to the marked voltage but that could be a waste of time and money. If you could find the schematics or examine the input circuitry you could reduce the risk of using a higher voltage to almost zero. It looks like there are several options available, it is up to the OP to decide what works best for the situation.

[Behemot]

Re: 19v adapter to 16v?

If it is laptop motherboard intended for 16-20 V, than using anything between 12 and 25 V is OK. No research needed, that is just the fact.

[tom66]

Re: 19v adapter to 16v?

Except a lot of tantalum capacitors, schottkies, MOSFETs are rated to 20V and may experience breakdown if they happen to be used above 20V? I did try an old laptop once. 19V input and it works at 17~18V before the charge LED goes out, there is often an under-voltage lock out which occurs very early because the laptop needs to detect the moment at which adapter power is gone and switch to battery immediately. Any delay caused by a wide-range input voltage results in a laptop which crashes when power is disconnected.

[Behemot]

Re: 19v adapter to 16v?

If you have 19V input than using 20V FETs and capacitors is just insanity. Laptop manufacturers are not insane so you will find at leas 30V FETs and 25V caps.

As for going down, well, worst case is it won't power but definitelly do no harm.

[japlytic]

Re: 19v adapter to 16v?

I tried to make an AC adaptor with a 19V output and a UC3842 switching controller output 15V, but the undervoltage lockout circuit becomes active, which means there is just enough headroom in the primary side low voltage rail for the UC3842 when run at its original 19V on the secondary side.

[spleenharvester]

Re: 19v adapter to 16v?

Thankyou guys, I think 19V is probably okay looking at the motherboard schematic, all the components in the area seem to be rated for at least 30V. I'll probably try that then. Cheers!

[spleenharvester]

Re: 19v adapter to 16v?

Wow, just looked again, even though the laptop says 16V on it the schematic says 19.5V in. Guess that confirms it haha!