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Hi guys,
I'm currently using LCDPS with jumpers across R1-R4, AC input is 9V and output is 5.25V. Load is 500mA (BII with Tridents).
When it used with default resistors (2.7R) voltage sags with 9V AC input.
Questions regarding that:
1.Do I need to increase AC voltage (12V) to be able to use default resistors?
2.Or decrease resistors value to something like 1.2R?
Another questions:
3. Here (http://www.twistedpearaudio.com/forum/default.aspx?g=posts&t=1892) in the last post Russ mentioned that L1 and L2 were doing nothing, so they can be ommited?
4. One side of my LCDPS is acting kind of strange, output voltage is floating a little (0.1V), other side is rock solid at 5.25V. What can I check and replace to repair that?
Thanks,
Fedor
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Is that an old LCDPS? Given 2.7ohm resistors it sounds like a new version, are they 3W? The load possible for the new model should be above the 500mA you mention.
Increasing input voltage increases the difference between input and output voltage of the regulator. That doesn't sound like a good idea in this case.
Can't comment on the L1/L2, but that sounds like an older version.
I'd check the soldering first.
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A:
1: yes. 2.7 ohm and 500mA is 1.35V and if you have two of those, then it is 2.7V. The bridge drops probably 1V and the regulator requires 3V headroom. So total about 6-7V headroom. For 5.25V output You would like 11-12V DC. A 9V AC gives you 9*1.4=12.6V DC, so you are in the borderline.
2: yes. Whichever is easier for you...
3: yes. They "do nothing" because there is a regulator after the CLRC filter
4. What do you mean "floating" do you mean fluctuating?. If that is the case, do as LeonvB indicated and then if that does not work, replace the regulator.
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Hello LeonvB and glt. Thank you both for your answers. Useful and informative as always.  @LeonvB Quote:Is that an old LCDPS? Given 2.7ohm resistors it sounds like a new version, are they 3W? The load possible for the new model should be above the 500mA you mention. You are correct - it is new version. Yes, Russ mentioned somewhere that it should be sufficient to power BII with Tridents, but looks like not in my case. Quote:Increasing input voltage increases the difference between input and output voltage of the regulator. That doesn't sound like a good idea in this case. Well, I'm gonna try both ways: lowering the resistors and increasing input (although increasing input will produce more heat, I think.) Quote:I'd check the soldering first. Thanks, this must be obvious choice for first-time troubleshooting. @glt Quote:1: yes. 2.7 ohm and 500mA is 1.35V and if you have two of those, then it is 2.7V. Thanks for the calculation, looks like headroom is too small indeed. Quote:2: yes. Whichever is easier for you... Will do both ways Quote:3: yes. They "do nothing" because there is a regulator after the CLRC filter Then I'll remove them later, if all is well. Quote:4. What do you mean "floating" do you mean fluctuating? Sorry, my english can be bad sometimes. Actually I meant that voltage is rising from 5.25 to 5.35 - 5.40. I suspected regulator too, and trimpot also. Will try to replace them after resoldering. Thanks, Fedor
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Rank: Advanced Member
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Joined: 11/3/2010(UTC)
Posts: 52
Location: Belgorod, Russia
Thanks: 6 times
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Hey guys,
just to close the topic - everything is back to normal.
To resolve my problem with fluctuating voltage I first replaced the trimpot, and it was the reason, as voltage is rock solid since that.
As to power consumption - I've tried 12V input while using default 2.7R resistors, and the output voltage didn't sag, but the regulator got quite hot, so I settled on 1.2R resistors and 9V input.
Thanks again for your valuable comments.
Fedor
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