LM317T & 2N3055 Regulator for 9.5V Laptop From 11.5-14V Solar/Battery System

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#1 21665658 30 Dec 2012 15:38

ed Kemp ed Kemp

Anonymous

Post #1
21665658 30 Dec 2012 15:38

hi, i know this is basic stuff but i have been away from the soldering iron for quite some time.

i live in the middle of nowhere and mainly use solar power/lead acid. problem is the stupid switch mode power supplies for the laptops are all fried one by one, 12v and 220v. it happens. but now i have none.

what i do have is an lm317 and a few 2n3055's and my 11.5v-14v solar/battery system. the silly laptops want 9.5v and wont accept a couple of hundred mV either side.

i built the standard circuit one would expect and the lm317 is stable but the output from the 2n3055 (2x in parallel) drops when i apply the load (up to 2 eeepc701 netbooks).

is there just not enough overhead of volts to regulate effectively?

now is not a good time to revise my theory, i need a working circuit and fast, and it has to be with these parts as i cant get anything else.

please help me, its boring as hell here with no music or proper internet access or movies. the netbooks run my projector and stereo, no other media fit devices here, just this old thin client running linux on a 300mhz cpu! if that gives up ........
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#2 21665659 30 Dec 2012 15:52

Cody Miller Cody Miller

Anonymous

Post #2
21665659 30 Dec 2012 15:52

Can you upload a schematic? I would like to see how you are using the 2n3055. How much current do you expect that you need? Also do you have any bulk capacitance that you can put on the output of you circuit?
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#3 21665660 30 Dec 2012 16:37

ed Kemp ed Kemp

Anonymous

Post #3
21665660 30 Dec 2012 16:37

sorry, but i cant send images and dont have a link. heres a basic rundown,

1.4k from adjust to ground
220 from adj to out
10 from out to final output from emitters 2n3055
out conected to bases of 2n3055

100nf from in and out of 317 to neg rail
100nf final out to neg rail

2n3055 x2 in paralel

that was the basis....

then i tried removing the 10r... no difference
then moved 220r from adj to adj-final output.... no better.
then i removed the 220r and linked adj straight to final output rail.. no better

the laptops draw between 100ma and 2 amps each original smp rated 2.5a

the power tr's bolted to heavy ali heatsink/case from a cb amp, (+chassis )
lm317 is clamped on a mica sliver with heat paste. nothing gets very warm.

hope that makes sense cody, make my day so i can watch that xmas episode of doctor who!
#4 21665661 30 Dec 2012 17:00

ed Kemp ed Kemp

Anonymous

Post #4
21665661 30 Dec 2012 17:00

i have a few electrolytics, 1000mf or about that, can scrap some boards if needed
#5 21665662 30 Dec 2012 17:10

ed Kemp ed Kemp

Anonymous

Post #5
21665662 30 Dec 2012 17:10

willing to start again from scratch for a circuit that will definitely work. i have:

2x 2n3055, 1x lm317t, enough resistors to make any value i dont have, capacitors but not many power grade (remember im using 12v dc input), and several 1n400x diodes from scrap gear (may help drop a few volts.)

i need the output to stay +- 200mv of 9.5,

input current available is 100+ amp from lead battteries, voltage range is from 11-14.5v.

output current i hope to be 0 to 5 amp without affecting output voltage.
#6 21665663 31 Dec 2012 03:12

Earl Albin Earl Albin

Anonymous

Post #6
21665663 31 Dec 2012 03:12

It is highly likely that your regulator doesn't have enough headroom and that's why it drops out. You need a low dropout linear regulator so go look one up on the Web, something capable of say 3A with Vce < 1V or so. You can't find one make one. They are simple & cheap. There you go.

By the way the electronics, etc, are not stupid because they do what Mother Nature has intended. You may not like it but you can become the master of the situation if you simply take time to understand what is going on & choose to let Mama work for you.

You can use about 5 parts, $1 in cost to make your regulator. Slam dunk.
#7 21665664 31 Dec 2012 03:22

Peter Evenhuis Peter Evenhuis

Anonymous

Post #7
21665664 31 Dec 2012 03:22

Hi ED,
I have a other solution.
The EEEPC 701 does work from 12 V see.
"klick link(eeepc 701 on 12v)":http://wiki.eeeuser.com/hardware_power_consumption#using_a_12v_battery

i used mine several times during long car travels on that way.

just make sure that you are not charging the 12 volt battery at the same time.
If you have a old CB unit you will find a few power diodes to drop voltage a little and protect.

And yes my EEEPC is my little life line to the civil world.

Update:

see below link
"click link to ASUS(asus)":http://eeepc.asus.com/au/accessories1.html?n=2

It is a ASUS original power supply as well for the 700 serie and the output is 12v 3Amp.

Just make sure not to feed 13Volt and more.
#8 21665665 31 Dec 2012 04:52

ed Kemp ed Kemp

Anonymous

Post #8
21665665 31 Dec 2012 04:52

ok i revise the use of the word stupid from applying to smpsu's to only applying to modern economic theory, ie; build it as cheap as posible and when it fails we can sell another unit.

also i draw your attention to the fact that i live 'in the middle of nowhere' ie; i dont have radioshack ten minutes down the road. im snowed in at the moment and when it thaws i still have a 2 hour 4x4 trek to the nearest village where i will be lucky to get basics like wood, petrol, beer, hammer. mama nature is firmly in control.

as for dropout, well really that was one of my original questions, trouble is how to get round it. practical circuits please only!!! i have the parts listed, also a bag of general purpose npn transistors, about 50 glass valves, and a multimeter.
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#9 21665666 31 Dec 2012 05:06

ed Kemp ed Kemp

Anonymous

Post #9
21665666 31 Dec 2012 05:06

im not sure if the eastern europe model 701 are different, but i can assure you that these ones (i have 3 for the family) do not like 12 volts or anything near. they go to protection mode where the charge led flashes but wont suck power. the last charger to die was a car charger and it failed high, ie the output went up to the full 12. maybe the usa domestic market demands better input voltage acceptance. the 701 is very popular here as it was the first netbook normal bulgarians could afford (just about afford) but that was 5 years back and the stores in the bigger cities dont carry spares, just try to sell a wrong charger thinking im an idiot, plus here you cant take bad products back for a refund, they will laugh in your face.
its a different world, but we do have an amazing amount of freedom, low taxes, better gun laws, not the nanny police state in the uk where i came from.
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#10 21665667 31 Dec 2012 05:18

Peter Evenhuis Peter Evenhuis

Anonymous

Post #10
21665667 31 Dec 2012 05:18

Make sure that the battery is not charged at the same time. use a diode as protection and drop a little the voltage or use two in series to drop more.
I have the same if my engine runs it does not work because of the charger but as soon the engine is off, the EEEPC is charging normal.
The same model is sold world wide with only a different cable and or battery capacity.
#11 21665668 31 Dec 2012 17:03

Steve Lawson Steve Lawson

Anonymous

Post #11
21665668 31 Dec 2012 17:03

OK, had some fun with this -- and now the disclaimer: Analog design in NOT my forte, but, since no one else has offered anything like this, here it is:

The CircuitLab link:

* https://www.circuitlab.com/circuit/c2s896/eeweb_9_5vregusing2n3055s_02/

and a PNG is attached.

R7 represents your laptop(s). This is not the most efficient circuit, and it will loose _regulation_ slightly above the minimum specified voltage (11.5V). I italicized _regulation_ because, the regulation on this thing isn't the best, and possibly might not conform to your specification of "a couple of hundred mV either side".

With a PNP power transistor I could, probably, make a low drop out version of this that would work down to 11.5V. It _will_ work down to 11.5V if Q4 is removed, but R4, R3, R6, R8 & R9 would all have to be divided by around 30, which would put quite a drain on your battery (i.e. even more inefficient!).

Also, I left it to you to work out the resistor wattages.

Perhaps one of the analog designers, out there, will jump in and spruce this up
#12 21665669 03 Jan 2013 16:59

Joel Sparks Joel Sparks

Anonymous

Post #12
21665669 03 Jan 2013 16:59

Try this.
#13 21665670 04 Jan 2013 14:14

Steve Lawson Steve Lawson

Anonymous

Post #13
21665670 04 Jan 2013 14:14

BTW: regarding the fried switchmode supplies: perhaps due to stepped sinewave approximation in inverter? Not sure if that is even a factor--I have no experience with this, but thought I would throw it out there.
#14 21665671 22 Feb 2013 23:46

Momename Garaipoom Momename Garaipoom

Anonymous

Post #14
21665671 22 Feb 2013 23:46

This circuit may be similar what you want.

I also using linux-ubuntu on thinkpad x100e.
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Topic summary

✨ A user with a solar/lead-acid power system (11.5–14.5 V) seeks to build a stable 9.5 V linear regulator for multiple Eee PC 701 netbooks, using only an LM317T and two 2N3055 transistors in parallel. The laptops require a tightly regulated 9.5 V ±200 mV supply and draw up to 5 A total. The user’s initial circuit, based on a standard LM317 with 2N3055 pass transistors, experiences voltage drop under load, likely due to insufficient voltage headroom (dropout voltage). Attempts to adjust resistor values and remove emitter resistors did not improve regulation. Suggestions include adding bulk capacitance, using diodes to drop voltage, and considering low dropout regulators or PNP pass transistors for better performance. Some responders note that the Eee PC 701 can operate on 12 V directly, referencing official ASUS power supplies rated at 12 V/3 A, but the user reports regional model differences causing protection mode activation at 12 V. A shared CircuitLab schematic demonstrates a possible regulator design with noted inefficiencies and limited regulation near the input voltage minimum. The discussion highlights challenges of linear regulation with limited parts and low input-output voltage differential, emphasizing the need for low dropout solutions or alternative approaches given the user’s remote location and limited component availability.

FAQ

TL;DR: Need 9.5 V ±0.2 V at up to 4 A for two EeePC 701s? "You need a low dropout linear regulator." Use LM317 + 2N3055 only if you keep headroom, or feed 12 V with a series diode when charging is off. [Elektroda, Earl Albin, post #21665663]

Why it matters: This FAQ helps off‑grid tinkerers power 9.5 V laptops reliably from 11.5–14.5 V solar/lead‑acid systems with the parts on hand.

Quick Facts

Input source: Approx. 11–14.5 V from a lead‑acid solar/battery bank available with high current. [Elektroda, ed Kemp, post #21665662]
Output target: 9.5 V with ±200 mV tolerance; user hoped for 0–5 A range. [Elektroda, ed Kemp, post #21665662]
Typical load: Each EeePC 701 draws ~0.1–2 A; original SMPS rated 2.5 A. [Elektroda, ed Kemp, post #21665660]
Root cause of droop: insufficient headroom/dropout in LM317 + pass transistor stage. [Elektroda, Earl Albin, post #21665663]
Field tip: Some EeePC 701 units accept 12 V directly; add series diode(s) and avoid charging simultaneously. [Elektroda, Peter Evenhuis, post #21665667]

Why does my LM317 + 2N3055 regulator sag when I load it from 11.5–14 V?

Because the regulator lacks headroom. The LM317 needs dropout across itself and any pass device. With low input, the 2N3055 stage falls out of regulation and voltage drops. As one expert put it, “You need a low dropout linear regulator.” [Elektroda, Earl Albin, post #21665663]

How much current should I plan for an EeePC 701?

Expect about 0.1–2 A per laptop during use. The original switch‑mode supply was rated 2.5 A, which aligns with brief peaks. Two units can reach ~4 A combined under load. Size wiring, fusing, and heatsinking for these currents. [Elektroda, ed Kemp, post #21665660]

Can I run an EeePC 701 straight from 12 V?

Yes, some users report the 701 runs from 12 V. Use a series power diode to drop voltage a bit and protect against reverse flow. Do not power it while the battery is being charged, since charging raises bus voltage and can trip protection. [Elektroda, Peter Evenhuis, post #21665664]

How do I drop a little voltage safely from 12–14 V?

Insert one or two series power diodes on the positive rail. Each diode adds a small drop and reverse‑polarity protection. This simple method helps when the engine/charger is off, preventing overvoltage to the laptop. Add more diodes if your system idles high. [Elektroda, Peter Evenhuis, post #21665667]

Is there a low‑dropout approach with my parts?

A PNP‑based pass stage can form a lower‑dropout regulator than an NPN emitter follower. One shared design note states a PNP version could meet 11.5 V input limits more comfortably, whereas the shown NPN stage loses regulation near the minimum. [Elektroda, Steve Lawson, post #21665668]

What resistor values did the OP try around the LM317?

Adjust to ground was 1.4 kΩ, adjust to output 220 Ω, and a 10 Ω from output to final node. The 2N3055 bases tied to the LM317 output. Several variations were tried, including removing the 10 Ω and changing the adjust connection, without improving droop. [Elektroda, ed Kemp, post #21665660]

Do two 2N3055s in parallel fix the droop?

Not by themselves. The OP used two 2N3055s in parallel and still saw the output collapse under load. The fundamental limit was input headroom, not just transistor current capability or heatsinking. [Elektroda, ed Kemp, post #21665658]

What bulk capacitance should I place on the output?

Add bulk capacitance at the regulator’s output to support transient load steps. A contributor specifically asked about adding output bulk capacitance to stabilize the laptop load and reduce sag. Large electrolytics you have on hand can help. [Elektroda, Cody Miller, post #21665659]

What input range should I design around in a solar/lead‑acid setup here?

Design for roughly 11–14.5 V at the regulator input. Your control strategy must maintain regulation at the low end and protect the load at the high end. This span defines the required dropout and dissipation window. [Elektroda, ed Kemp, post #21665662]

Is there a ready‑to‑try schematic from the thread?

Yes. One member shared a full schematic and simulator link showing a 9.5 V regulator using power transistors, along with notes on its regulation limits near 11.5 V input and efficiency trade‑offs. Start from that and adapt. [Elektroda, Steve Lawson, post #21665668]

Why did my car laptop charger fail high to 12 V?

The OP reported a charger that failed high, outputting the full 12 V and tripping the laptop’s protection. That failure mode is a known edge case; design your fallback to tolerate a direct 12 V bus if possible. [Elektroda, ed Kemp, post #21665666]

What quick steps get me running today without new parts?

Disconnect any charger so the bus sits near 12 V.
Insert one or two series power diodes to drop and protect.
Connect the EeePC 701 and verify charge LED shows normal behavior. This field method avoids low‑headroom regulation issues. [Elektroda, Peter Evenhuis, post #21665667]