Rare transistor LM6852D

[Paulo Trindade]

Hi. I'm trying to repair a small 220V to 12V power source, where I found 2 LM6852D NPN shorted. I can't really find the same reference for sale, so I'm trying to find a replacement. I asked local shops but none could supply me with an equivalent.
Now I've been trying to input the specs for the mosfet on online stores, but I put in VDS 400V or 450V, VGS 8 or 10V, and I get 0 results. Am I doing something wrong?

Can you help me find a replacement reference?
I've uploaded the spec sheet online (it was hard to find):
https://app.box.com/s/6q9hyn6t1wurxlgacwtl

Thanks

[Andrew F. Ali]

Re: Rare transistor LM6852D

This is a NPN Bipolar transistor ia Darlington arrangement with a Damper Diode. Rare indeed as I don't think I've ever seen a transistor coded with LMxxxx. I usually see 2SA, 2SB, 2SC or 2SD.
I'm guessing it is a Power Supply Regulator or Horizontal Output?

[redwire]

Re: Rare transistor LM6852D

It's an oddball transistor, only because it also has a built-in switch-off transistor, to speed turn off time.
I would use any 600V beefier TO-220 sized part if it will fit. But I can't find any with a built-in reverse diode.

[Paulo Trindade]

Re: Rare transistor LM6852D

This is a NPN Bipolar transistor ia Darlington arrangement with a Damper Diode. Rare indeed as I don't think I've ever seen a transistor coded with LMxxxx. I usually see 2SA, 2SB, 2SC or 2SD.
I'm guessing it is a Power Supply Regulator or Horizontal Output?

It's a part of this power supply: https://app.box.com/s/kqp5ml16i1ubuxq6ye6k

Pretty simple layout, and on the other side of the transformer there are just 2 white wires and two red ones (220V in, 9~12V out). Both mosfets died.

I'm thinking I'll just open up a common 220V to 12V adapter and replace the whole board.

[Andrew F. Ali]

Re: Rare transistor LM6852D

These 2 transistors are shorted. With transistors with this internal arrangement they may be good and showing as bad when tested with an multimeter. Share a copy of the TV's circuit diagram and I may be able better to help you. Did you check those diodes for shorts and Resistors for open circuit?
NOTE: the transistors are NOT mosfets (Metal Oxide Field Effect Transistors) but are Bi-polar (BCE)

[kasfamily]

Re: Rare transistor LM6852D

May be use BU808DFI http://pdf1.alldatasheet.com/datashe.../BU808DFI.html

[Paulo Trindade]

Re: Rare transistor LM6852D

These 2 transistors are shorted. With transistors with this internal arrangement they may be good and showing as bad when tested with an multimeter. Share a copy of the TV's circuit diagram and I may be able better to help you. Did you check those diodes for shorts and Resistors for open circuit?
NOTE: the transistors are NOT mosfets (Metal Oxide Field Effect Transistors) but are Bi-polar (BCE)

All the other components were tested, and they are fine. All diodes, caps, and resistances measured and verified.
Legs 1 to 2 (base to emiter I believe) are shorted on one transistor, the other has a very low resistance value (voltimeter still beeps).
Edit: These were tested outside, I pulled them out before I tested them.

It's not a power source for a TV. It's just a simple converter to feed a 12V fan.

[Paulo Trindade]

Re: Rare transistor LM6852D

May be use BU808DFI http://pdf1.alldatasheet.com/datashe.../BU808DFI.html

Those specs are a bit different. Are you sure they will work on that circuit?

[budm]

Re: Rare transistor LM6852D

LM6852 is not DARLINGTON type, BU808DFI is DARLINGTON.

[kasfamily]

Re: Rare transistor LM6852D

BU808DFI use in horizontal output tv. Show the whole scheme

[redwire]

Re: Rare transistor LM6852D

That looks like a cheapola electronic transformer for 12V halogen lamps, like this circuit: ST Microelectronics App Note 3902
Suggest BUL38D or BUL39D which are bigger TO-220 package, but common.

[Paulo Trindade]

Re: Rare transistor LM6852D

BU808DFI use in horizontal output tv. Show the whole scheme

Here's the whole board (notice the extra 4 diodes on the out wire).

[Paulo Trindade]

Re: Rare transistor LM6852D

That looks like a cheapola electronic transformer for 12V halogen lamps, like this circuit: ST Microelectronics App Note 3902
Suggest BUL38D or BUL39D which are bigger TO-220 package, but common.

I believe you are right. This board is similar to the ones on the lamps, and those transistors you point out might do the trick.

Thanks

[Andrew F. Ali]

Re: Rare transistor LM6852D

Since this Power Supply is for a fan and not to supply power to work the TV I would suggest replacing the entire thing with one of those self contained units. Cut out the jack and connect the +ve and-ve directly to the fan.

[Paulo Trindade]

Re: Rare transistor LM6852D

Since this Power Supply is for a fan and not to supply power to work the TV I would suggest replacing the entire thing with one of those self contained units. Cut out the jack and connect the +ve and-ve directly to the fan.

Hi, I did that ealier today. I might eventually try to fix the original one, but for now that was clearly the easiest way to get it working.

Thanks to everyone who expressed their opinion

[erichgamba]

Re: Rare transistor LM6852D

In a CFL bulb I replaced the LM6852D with a BLD123D and it works.
Link to BLD123D data-sheet