LED Driver unit with no output

[(*steve*)]

Before you power it up, check the resistances between the pins. The resistance between ground and output should be significantly higher in one direction vs the other (i.e. with the probes reversed).

Also be very sure to put the diode in the correct way!

 

[partyanimallighting]

Well, the SR160 is not available. Neither is the SB3100E. I got an NTE replacement, NTE578. It's the same type of Schotty Barrier Rectifier but the datasheet I got is very vague (and I don't really know what I'm looking for when I read it). It's rated at 1A 90V. Will this function properly?

 

[partyanimallighting]

I tested the NTE578 prior to installation and got 0.28VDC from one side and OL from the other and I think this is correct because the diode is supposed to allow current flow in one direction only according to the info I read. I then installed the NTE578 and checked readings at the LM2575 pin sockets ( the regulator is not installed) and they are as follows:

PIN 3 (+ lead) to PIN 2 - 14.5KΩ
PIN 3 (+ lead) to PIN 4 - 14.5kΩ
PIN 3 (- lead) to PIN 2 - 6.25KΩ
PIN 3 (- lead) to PIN 4 - 6.27KΩ

Do these readings look correct?

 

[(*steve*)]

They certainly look a lot better.

The diode you have should be ok. If you had told me where you were I could have tried to find you something locally.

 

[partyanimallighting]

I'm in Trinidad in the West Indies. If the unit powers up, I'll still order spare SR160's and SB3100's just in case. I'll install the regulator, power up, and update you in a bit.

 

[(*steve*)]

OK, West Indies is a new one for me. You clearly have a local supplier. Who are they, and do they have a web site?

 

[partyanimallighting]

Yes they do. http://www.steveselectronics.biz/
But I normally purchase hard to source parts from Digikey and have them shipped down to me but I normally have to let the order build up to a sizable amount then order. On to the good news. I installed the NTE578, powered up and everything appears to be working fine. So I just have to clean up my cruddy solder points, reassemble and reinstall the unit. I'll put in a larger heatsink but I was also considering mounting a small fan near to the regulator also. I do have a lot of small 12VDC fans available but the question is, does the circuit board have a 12VDC source? On to the next repair!

 

[partyanimallighting]

 

[(*steve*)]

Good job repairing that, and I'm sorry I dismissed the diode as the cause initially :-(

I had a look at the web site of your supplier, but I couldn't find any listings for discrete components, so I can't advise you as to a better diode if this one fails again.

The general rule would be a Schottky 60V or higher diode, with a current greater than 1A It is the latter specification which is most likely to matter. If you can obtain a 2A or 3A diode, that would be better.

However, I would hope your repaired unit will now give you a long service before it needs your attention again. Given that it was the diode which failed, a larger heatsink on the regulator is probably not warranted. Stick your finger on it after it has been running for a while (under normal load conditions) and see if it feels too hot. If you can hold your finger on it without any risk of burning yourself then it is fine.

 

[(*steve*)]

If it does fail again, you might try an NTE573 (although I am a little concerned about it's reverse leakage). Those worries would be largely eliminated if an NTE573-1 were available.

 

[partyanimallighting]

I'll probably order a couple of the SB3100's and SR160's in the interim from Digikey just in case and keep them on hand. I checked the NTE573-1 datasheet and I see that it handles a higher voltage so I'll keep that in mind when I'm ordering. I've started a new thread as I'm trying to modify a keyboard but no one seems interested **sigh** so I haven't gotten any responses. If you have some time, can you take a look at it?

https://www.electronicspoint.com/threads/tg3-electronics-keyboard-modification.273647/

 

[(*steve*)]

Don't order anything from digikey just yet. I'll take a look at what's available and recommend something. The device I recommended was just the first on the list and is neither the cheapest not the best performing.

I'll also try to figure out what's going on in the other thread, but from an initial read I'm not certain I can help.

 

[partyanimallighting]

OK. I'll wait for some more feedback on both threads. I'd appreciate and views or workarounds on the other thread. It's a great piece of equipment and it's sitting down in pieces waiting on a solution.

 

[partyanimallighting]

OK. I'll wait for some more feedback on both threads. I'd appreciate and views or workarounds on the other thread. It's a great piece of equipment and it's sitting down in pieces waiting on a solution.