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DC-DC converter driver IC .. MNAJ S14B

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Hi Guys,

I’m hoping someone can help me please.

I have a pretty expensive ($1000+) electronics module to repair which has a tiny DC-DC convertor on board to run two seperate 5 volt outputs.

One supply runs the micro etc and the other runs the communications section.

There is a small 3mm square 8 pin driver IC with the label “MNAJ S14B” (on two lines) .. which drives an IRFR220 Mosfet.

Both are faulty and while the Mosfet is readily available … I cant find any reference to the IC anywhere !!! … despite hours on the net.

I have drawn out the circuit and the following are the pin outs …

Pin 4 & 5 go to ground
Pin 8 is the supply (22volt)
Pin 6 is the drive to the MOSFET Gate
Pin 1 connects to the MOSFET Source .. which also has a pair of 1 ohm
resistors in parallel to ground .. current monitoring I assume.
Pin 3 has a 20k to gnd. and an 84.5k resistor to the secondry of the transformer
Pin 7 .. also has a 84.5k resistor to another point in the secondry

Just wondering if anyone recognises the IC number … or the connections.

The board has the date of 2001 printed on it, so is not particularly old, and it was built in the US.

Hoping someone can help.

Regards, Wes.


Hi John, thanks for the response.

It's out of a Boumatic pulsator control board out of a dairy .. a 'prism' pulsator.

It has a very basic function, but with lots of added complexity with communications back to the main network controller etc etc

If I were able to find schematics for some of this stuff, I'd feel like I'd hit the jackpot. I'm so used to having to work it all out for myself ... drawing out bits of the circuits to find my way around.

If you hear of anyone who worked for Boumatic, and who have access to some circuits .... :D

Hi Eric, thanks for your input as well.

Yeah .. despite the small size, it's definitely the correct numbers. I've been able to eyeball two seperate boards with the same IC.

Success ... in the mean time, I've had a response from another forum that I frequent .. and I've been told that it's a National IC .. LM3478


I've asked how he knew .. but haven't had a reply yet.

The data sheet lists the numbers that I was after ... the thing that amazes me is why they bother to put some dud number on it when there was room for the proper number in the first place.

Any way .. this one is solved .. but stay tuned, I'm always on the look out for some odd bit :confused:

Thanks again for your help.

Regards, Wes.


Hi John,

Well. The Datasheet tells you it is marked S14B
Yeah ... I discovered that too, once I'd downloaded the datasheet .. the point is that I never would have discovered that if someone else hadn't told me what datasheet to look at :)

What I was saying that if they had room to write MNAJ S14B on the actual IC ... they might just as well have written it's proper name .. LM3478 like most manufacturers do on most components ... at least the ones I see. :)

I've just finished fitting the new IC and mosfet .. and it works ok ... hooray .. the interesting thing is that the new IC is labeled " MEAN S14B " ... which I figured is appropriate. :)

Thanks again for your help.

Regards, Wes
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