Looking for simple DC reducer

I came across a free toshiba laptop but no adapter. It needs 15@3A and I have an adapter that is 18.5V@3.8A. Can someone recommend a nice simple way to reduce the 18.5 down to 15 leaving the amps unchanged? Would a string of rectifiers (like 5)do this safely? I don't want to pony up the 30-40$ for a new adapter only to find the laptop has a dead screen or something. And feel free to talk down to me since I know only enough to be dangerous :D

thx

Stu

The operative word here is "dangerous". IFF you take the battery out, you can probably get away with just about any 15V ish source. Depenging on the nominal battery voltage, it may run just fine on 12V. But the charge current limit for the battery MAY depend on the AC adapter. You don't want to make smoke/fire. Since you gave no clue to the model, age, battery technology, YMMV. mike

--
Return address is VALID but some sites block emails
with links.  Delete this sig when replying.
.
Wanted, PCMCIA SCSI Card for HP m820 CDRW.
FS 500MHz Tek DSOscilloscope TDS540 Make Offer
Wanted, 12.1" LCD for Gateway Solo 5300. Samsung LT121SU-121
Wanted 12" LCD for Compaq Armada 7770MT.
Bunch of stuff For Sale and Wanted at the link below.
MAKE THE OBVIOUS CHANGES TO THE LINK
http://www.geocities.com/SiliconValley/Monitor/4710/

Actually about 3 or 4 diodes in series would do the job. Say 4 x 1N5401/2/3/4 etc. They're rated at 3 A but not sure if they'll dissipate that happily in free air.

The 15V input requirement of your Toshiba laptop is unlikely to be critical - there'll be an inbuilt DC-DC PSU regulating the internal voltages anyway.

Graham

I built me a series linear regulator from a lm350T and it worked great in dropping the voltage down to 15 from 18.5 but it also shaved 3A off the supply so I'm not sure if I just read the datasheet wrong. I'll try the series diodes now and see how this fares. Its a shame I really liked my cobbled linear regulator...thx for all the tips so far!

Stu the laptop is a toshiba 2100cdt with a 10V@2600mAh battery thats likley about 6 years old (i.e. dead)

Oh can anyone confirm that hooking the 18.5V up to the laptop would harm it? I've been offered advice to do just thought but my thoughts are they made the power pack 15V for a reason....

way

of

a

The regulator dissipates (18.5 - 15)*3 = 10.5 W, and the thermal resistance from junction to ambient is either 35 or 50 K/W depending on which package you chose. What kind of heat sink do you have on there? You'll need a pretty big one. Also, get the steel (K) package if you can.

Jonathan

great in

great, job done.

did what??

NT

? 2005?5?6???? UTC+

8??1:48:40?S???

way

of

r a

China Shenzhen ZHAOWEI Machinery & Electronics Co. Ltd engages in designing , manufacturing and marketing all kinds of electric motors. They are mainly suitable for the following applications: smart home application used in sm art kitchen and laundry, medical instrument for personal care, smart E-tran smission applied in automobile, industry automation applied in telecommunic ation and a great variety of plastic/metal planetary gearbox in different s izes. In order to develop the oversea market, we are current seeking new partne rs around the world to create a bright future together. ZhaoWei is a right choice and excellent partnership with sincere services.

Company: Shenzhen ZHAOWEI Machinery & Electronics Co., Ltd URL:

Contact: Anny Liu Tel?+86-755-27322652 Fax?+86-755-27323949 E-mail: snipped-for-privacy@zwgearbox.com Add: Blk. 18, Longwangmiao Industry Park, Fuyong Tn., Bao?an Dist., Shenzhen 518103, Guangdong, China