Welcome Guest! To enable all features please Login or Register.

Notification

Icon
Error

Options
View
Go to last post Go to first unread
joseki  
#1 Posted : Saturday, March 21, 2009 9:01:19 PM(UTC)
joseki

Rank: Member

Groups: Member
Joined: 3/21/2009(UTC)
Posts: 2

Hi!

I have an board labeled Dual PS LC1 that I'm having a small problem with. My input is 18VAC+18VAC and I'd like to regulate down to 2x15VDC. However, I run out of adjustment room in the 5K pot and am a few volts above my target. Looking at the datasheet, it seems that this exact supply should go from 1.25-25V with an input of > 28VDC. This circuit is very similar to the datasheet. So my question is, does the resistor in the CRC need to be recalculated, or do I need to lower the 240R resistor used to set the output voltage.

Thanks!
Russ White  
#2 Posted : Monday, March 23, 2009 7:08:49 AM(UTC)
Russ White

Rank: Administration

Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 3,979
Location: Nashville, TN

Thanks: 25 times
Was thanked: 89 time(s) in 83 post(s)
Check the voltage at both ends of the CRC under your load. Then you will probably have your answer. :)
joseki  
#3 Posted : Tuesday, March 24, 2009 5:59:36 PM(UTC)
joseki

Rank: Member

Groups: Member
Joined: 3/21/2009(UTC)
Posts: 2

Russ:

Here's what I get:

Input is 18VAC+18VAC nominal. I measure under output load 20.8VAC+20.8VAC on the input to the board. I'm getting 1.50V and 1.54V drops across the resistor in the CRC supply. The lowest voltage I can get across the output is 22.4VDC and -21.4VDC. There is 24.6 VDC at the input to the CRC and ~23VDC on the output of the CRC. I'm using a pair of 3.3K resistors as load, which models my target current at the intended 15VDC output. On the LM317 I get 0.25 VDC on pin1, 23.2 VDC on pin2, and 22.4 VDC on pin 3, measured with reference to ground. On the LM337 I get 0.20VDC, 21.4VDC, and 23.0VDC on pins 1, 2 and 3 respectively.

I'm assuming the regulator has enough head room to operate. The heat sinks on the regulators get warm.

Any ideas what is happening?

Thanks!
Brian Donegan  
#4 Posted : Wednesday, March 25, 2009 10:04:46 AM(UTC)
Brian Donegan

Rank: Administration

Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 2,798
Location: Massachusetts, USA

Thanks: 2 times
Was thanked: 127 time(s) in 122 post(s)
Are the LM317 and LM337 on the correct sides? The 317 should be IC1 and the 337 should be IC2 (I assume this is the LCBPS). Your symptoms sound like reversed vregs.
Rss Feed  Atom Feed
Users browsing this topic
Forum Jump  
You cannot post new topics in this forum.
You cannot reply to topics in this forum.
You cannot delete your posts in this forum.
You cannot edit your posts in this forum.
You cannot create polls in this forum.
You cannot vote in polls in this forum.