Led Work Lamp Repair Help

[artanis]

Hello,
I have this LED lamp that I am trying to fix. The main issue from what I reckon is a burnt component on the PCB and being chared completely I cannot identify the darn thing. The PCB has 3 components marked with the D symbol (D1, D2, and D3) and I hoped that all of these are the same but the D3 footprint seems different from the others.

I am guessing the D1 and D2 are fine since they don't look burnt but I did a google search on the markings on them ("KT1060 08K21") and couldn't find out what they are. Are these special components custom made for the company that made this lamp?

Any help with this is greatly appreciated. Thanks!

[artanis]

I think I figured it out.
I guess that was a diode used mostly for reverse voltage protection. After desoldering the burnt part there was a diode marking on the PCB so I just replaced it with a generic diode.

[fzabkar]

KT1060T, Huaksemi, Schottky barrier rectifier, 60V, 10A, TO-227:

https://www.kingtoelec.com/UploadSysFiles/files/%E8%82%96%E7%89%B9%E5%9F%BA%E6%95%B4%E6%B5%81%E4%BA%8C%E6%9E%81%E7%AE%A1/KT1045T-KT10100T-TO277-V25A22.pdf

[elecdonia]

What are the voltages at the anode and cathode of the replaced diode in relationship to the negative lead of the input power cable?
There are two possibilities:

1) If the diode is connected as a "reverse polarity crowbar" it's cathode will be +12V, anode will be 0V. Unfortunately this configuration may cause the diode to explode if the external power source can provide a very large short-circuit current (for example a car battery). However if an input fuse of reasonable size (<5A) is present then the fuse will blow before the diode gets damaged. Ordinary diodes can survive very large surge currents for a few msec (long enough for a fuse to blow).

2) More commonly the diode is in series with the positive input wire. Anode to positive input wire, cathode to the powered device. For this case the anode of the diode will be at 12V (or whatever the input voltage is) and the cathode will be about 0.6V lower voltage. Diode failure is quite rare for this circuit arrangement. When the input polarity is reversed the diode simply does not conduct at all. However, some voltage is lost across the diode during normal operation, where the diode is conducting the entire operating current of the powered device. For a standard diode it is 0.6V. If a Schottky diode is used the forward voltage drop is lower, perhaps 0.25V.

I would be surprised if the original circuit design is #2 (with diode in series with power source). This lamp is rated for 12-48V input. I would expect the input current to be <1A at 12V, even less with a larger input voltage. I simply can't think of any situation where connecting 12-48V with reversed polarity would cause any damage to the diode. However, if somebody applied AC mains voltage at 120V or 240V, that certainly could explode the diode (and likely most of the other components on the PC board too.)

More likely the original circuit design has the diode connected to crowbar the reverse polarity (#1), in which case connecting a power source with very high short-circuit capability May cause the diode to explode. If this is the way the lamp is built, then a fuse is totally necessary. The fuse amperage rating should be no larger than twice the measured input current while operating with a 12V power source.

[artanis]

Hey, thanks for your detailed answer!
The circuit design is #1 in this case, cathode was at 12v if I remember correctly last time I checked.
This lamp was indeed powered by car batteries and the diode was pretty toasted. I will add a fuse to the circuit too.

[lowimpedance]

What is the part number on the IC ?  The function of that part might give a clue via a data sheet with an application cct.  I suspect the diode is part of converter. quite possibly another schottkey type.
After replacing the burnt diode with a generic one is the lamp functional again ?