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DELL PA-10 (PSU for high power LEDs) - VOLTAGE DROP 19,5V to 18,5V (by 1A)

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misiacik7

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Hi.

I have a DELL PA-10 90W adapter. I want to power some LEDs. But there is a problem. When there is some load, the voltage drops.

I think it is caused by feedback that i dont use... (cause I dont know how).

How to get it working? I now use only positive and ground "cables" of it, i dont use the cable i was told it is a feedback.

Thanks in advice :)
 
Read this link and you will understand exactly what the third wire is all about. This is normal on most laptop AC adapters.

Unless there is no longer a laptop this unit is used with I suggest you not mess with it if you actually need it.

Ron
 
The adapter is looking for the laptop it is designed for use with. What exactly are you trying to use it for? If you open it up, then yes, it could likely be hacked to use as a basic power supply of sorts and keep in mind it was designed to charge a battery with controlled low current. **broken link removed** shows a few that have been opened and what you can expect to see. Again, what are you using it for? Just some LEDs? A drop from 19.5 to 18.5 isn't all that much.

Ron
 
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RAIL (A) = 4 x 2,5W (4V * 700mA) = (4 * 4V = 16V) – OK [TOTAL 1pcs]

RAIL (B) = 12 x RAIL (C) [TOTAL 8pcs]

RAIL (C) = (6 in series x 0,064W (3,2V * 20mA) = (6 * 3,2V = 19,2V) – NOT OK (19,2V < 18,5V) [used in RAIL(B)]


TOTAL amparage should be ,7A + 8*12*0,02A = 2,62A
Measured = less than 1,5A


The problem is that it is all built at the moment. I have built them 6 LEDs in series, cause there was 0,3V in reserve and put them into 12 parallels and wanted to put the 1R3 resistor 0,3V/(0,02*12) = 1,25 = 1R3

But now I dont use any resistor cause the drop of the voltage caused the rails is powered only by 18,5V and it is lower than the drop of voltage across 6xLEDs :(

When I measure current across RAIL (B) without a resistor (12x6 LEDs) the result is only 150mA and should be 20mA * 12 = 240mA

Another problem is that I want to have the ability to turn on/off RAILs (B). And every added load cause higher dropp of the PSU.
 
Here is the RAIL (B)

**broken link removed**

Here is the 12xRAIL (B)

**broken link removed**

I(should be) = (0,02A x 3 x 4) x 8 = 1,92A
I(measured) = (0,02A x 3 x 4) x 8 = 1,20A (caused by drop of Vin from 19,5V under 18,5V)
=> LEDs shine at app. 1.20A / 1.92A = 62.5%

Everything is build so I cannot modify such many LEDs so only way to let them shine on app. 90%
is to avoid the voltage drop by (telling the PSU to not drop the voltage) or to stabilize the PSU.
But i dont know how to do that :(

How to stabilize the PSU at level of 19,5V eventually 19,2V.
 
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Is there anyone who can help me with this issue?

Does anyone knows how to connect the feedback wire (3rd) to avoid the drop of the voltage?

Has anyone tried this MC34167 ?
**broken link removed**

Maybe is it stupid question, but does it stabilize the voltage??? I mean it is STEP UP/DOWN REGULATOR.

Vout = 19,2V = 5,05V * (R2/R1 + 1)

R1/R2 = 3,8 - 1 = 2,8

for example R2 = 5R6, R1 = 2R



Does it mean, if my input Voltage Vin will be 19,5V it will regulate and STEP DOWN the voltage to 19,2V and under load when it drops to 18,5V the regulater will STEP UP the Vout to 19,2V???

Thanks in advice
 
Figure 21 of the MC34167 data sheet does show a step up/down circuit that should do what you want. But the circuit must be built on a custom printed-circuit board such as Figure 22, not a breadboard (see warning on page 8 of the data sheet).

In general, you should use more than 0.3V of headroom when operating LEDs in series. It should be at least a volt to allow for manufacturing differences in the LED's forward voltage.
 
I cannot get the 1N5825, only 1N5820, 1N5821, 1N5822 is available.

Is the Cf, Rf, C1, C0, Cin calculated, or are they constants for that figure 22?

What is Cin = 330? 330nF, 330pF, 330uF? The same is with other capacitators...

What Vout should I use for such LEDs? Higher than 6*3,2V=19,2V?

Is there a need of heatsink for the IO? How "big"? For 2A current?

What is the L 190uH? Coil? Do I need the Gate resistor RG, zener diode D3 and D4 if my input voltage is little bit lower than 20V?

Thanks in advice :)
 
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The 1N5822 should work.

The values are as shown in the Figure 21 schematic.

All caps are µF.

You use the nominal voltage for the LEDs given in their data sheet.

The coil is as described just below the table beneath the schematic.

You should mount the device and transistor on a small heatsink, capable of dissipating about 4W.

You are close enough to 20V that I would recommend adding RG, D3 and D4.
 
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