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Question on Part Replacement

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LabTech

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Ok Guys,

You all helped me out tremendously with my last problem. Now I have another. I have an LCD TV that was given to me that is a Dell (i know they suck), Well this one has the infamous power on problem, and I believe I have isolated the problem, however I need to know something on a replacement part for this thing. The part I see that is bad is another part from Alpha Omega, partnumber AO4944, My question to you guys is this. Is the AO4946 able to be put into the circuit in place of the AO4944 as digikey does not carry the ao4944. I have attached the pdf's of the 2 parts and a schematic of the circuit they are used in. I am questioning the description on the pinouts of the AO4946 particularly where it says D1/S2. Can those pins be used as either Drain 1 and/or Source 2 of either MOSFET's? I do not understand what they mean by this. The spec sheet is identical between the 2 otherwise. Thanks in advance for your help.
 

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creakndale

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I believe there are 2 completely independant Mosfets in the AO4944 part but the Drain of Mosfet 1 is internally connected to the Source of Mosfet 2 in the AO4946 part. So the AO4946 is internally wired with Mosfet 2 "above" Mosfet 1 in a half bridge configuration whereas the Mosfets in AO4944 are independant.

Referring to Figure 1 in the NCP5422A PDF there are two potential locations for the AO4944...
1) On the right side, if Q1 happened to be the AO4944's D2,G2,S2 and Q2 happened to be the D1,G1,S1 then the AO4946 is a valid replacement as the schematic shows a connection from Q1's Source to Q2's Drain which the AO4946 does internally. However, it would not be a replacement if Q1 happened to be the D1,G1,S1 and Q2 happened to be the D2,G2,S2.

2) On the left side, if Q3 happened to be the AO4944's D2,G2,S2 and Q4 happened to be the D1,G1,S1 then the AO4946 is a valid replacement as the schematic shows a connection from Q3's Source to Q4's Drain which the AO4946 does internally. However, it would not be a replacement if Q3 happened to be the D1,G1,S1 and Q4 happened to be the D2,G2,S2.

This is only my opinion, though.
creakndale
 
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