Hello. I have a LM338 Buck converter that is TO-3 Package. I have it setup with a Diode Reverse Polarity protection. It is setup with L7812 for Fan and Led Display power. I have the TO-3 package mounted and was covered with a ITX sized Heat Sink and Fan. So Temperature hasn't ever been very high. This is setup with a 4700 uF 50v Cap input. Output is 2200 uF 50v. This is said to be Ideal Power input of 20v. So I had it running off a 19.5v input has worked very well for some time. yesterday I wanted to test one of my 1157 bulb for a replacement of one of my Sisters front blinkers. I don't normally use used Bulbs and when I change out one that is bad I will swap them both for reasons I just like the light to be same or close to same light output on each side. Anyway I don't normally test with this PS and when I connected my Test socket with a Bulb that looks new (Still working) The Lamp lite up for a blink like it just blew. Well looking at my Supply I see that the Display for Volt out is now going down to 000 and ended and stayed there.
So I took another Buck that I have running off a different Chip only 2amp output connected. It dropped downn to 3 volts as a Protection. However I took off and put back on and powered this over 2Amp and it lit the bulb without issue. Knowing that it did put this past it limits I wanted to check what the Current draw was 2.09A but this Cheap .99c Buck from China did ok. Just not something that I use often on large loads seeing it only 2A max. Plus no Heat Sink or fan. Worked just fine. Did heat up for the 30 seconds to minute that I tested the bulbs.
I guess My question isn't the LM338 rated higher then the LM2596? I have always used the LM338 Supply as a way to have constant stable power in my shed, Never questioned the current to anything that I would power and really didn't think 1 little 1157 on the Flasher/Brake element would have been enough draw to kill the LM338? I made the mistake of Installing the Back up 338 turned it on. Did some testing over some of my normal playing around with things and didn't ever take more then 1.58a. So I thought ok, Might just been tired older one, Took the bulb and socket as it was installed before. Connected as it should have been and did the same thing again. Only thing I did different this time was turned the Volts up to 12.8 rather then 12.3 that I had it set when the First LM338 stopped working!
When I tried to clean the heatsink paste off the chip with 99% Alcohol it took off the lettering on the packages of both. One was Marked ST that was the One I was using the first time and the last one was National with the side S looking mark. However like I said both while trying to take off putty from the HS the letters came off both so I think they are Fakes. I was under the impression that they were both over 5amp able chips. So now I need to replace this and get my PS back up on the Shed bench. Until then I guess I will have to use my HP6632 that I like to keep in my Garage on the work desk.
Anything that I can do to keep this from happening again in the future? Or know of a Good source to get Real LM338 that I can get back in this. I am not sure I want to buy from China with thoughts they might not be real. Also I don't like to have to wait for things to get here from China lol
James
So I took another Buck that I have running off a different Chip only 2amp output connected. It dropped downn to 3 volts as a Protection. However I took off and put back on and powered this over 2Amp and it lit the bulb without issue. Knowing that it did put this past it limits I wanted to check what the Current draw was 2.09A but this Cheap .99c Buck from China did ok. Just not something that I use often on large loads seeing it only 2A max. Plus no Heat Sink or fan. Worked just fine. Did heat up for the 30 seconds to minute that I tested the bulbs.
I guess My question isn't the LM338 rated higher then the LM2596? I have always used the LM338 Supply as a way to have constant stable power in my shed, Never questioned the current to anything that I would power and really didn't think 1 little 1157 on the Flasher/Brake element would have been enough draw to kill the LM338? I made the mistake of Installing the Back up 338 turned it on. Did some testing over some of my normal playing around with things and didn't ever take more then 1.58a. So I thought ok, Might just been tired older one, Took the bulb and socket as it was installed before. Connected as it should have been and did the same thing again. Only thing I did different this time was turned the Volts up to 12.8 rather then 12.3 that I had it set when the First LM338 stopped working!
When I tried to clean the heatsink paste off the chip with 99% Alcohol it took off the lettering on the packages of both. One was Marked ST that was the One I was using the first time and the last one was National with the side S looking mark. However like I said both while trying to take off putty from the HS the letters came off both so I think they are Fakes. I was under the impression that they were both over 5amp able chips. So now I need to replace this and get my PS back up on the Shed bench. Until then I guess I will have to use my HP6632 that I like to keep in my Garage on the work desk.
Anything that I can do to keep this from happening again in the future? Or know of a Good source to get Real LM338 that I can get back in this. I am not sure I want to buy from China with thoughts they might not be real. Also I don't like to have to wait for things to get here from China lol
James