Help identify IC and diode

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pman92
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Help identify IC and diode

Post by pman92 »

I've got my hands on a "DPF delete" module and I'm trying to work out how it works.
I think I've worked it all out hardware wise except this last circuit, which has this mystery SOT25 IC and SMA diode. The markings and circuit they are connected to is shown in the picture below. The "Output" is an EGT sensor input on the vehicle, so its trying to simulate a NTC thermistor. I'm thinking its possible the cars PCM may be measuring current through the sensor, rather than resistance via a voltage divider, hence the use of this circuit.

I've taken some measurements with it just powered up on the bench and found the following:
-There is a microcontroller feeding a 2khz PWM signal at 98% DC into the circuit via the 10K resistor.
-Therefor there is about 4.8v on what I'm guessing is the input to the IC
-Theres 2 pins connected together and running out to an EGT sensor input at the car's ECU/PCM. Its also about 4.8v with nothing connected.

MysteryParts.jpg
MysteryParts.jpg (126.12 KiB) Viewed 5249 times
Does anyone have any insight?

Thanks in advance
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picvrss
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Re: Help identify IC and diode

Post by picvrss »

I can't immediately identify the IC, but the SMA "diode" has markings that I would normally expect from a capacitor - in this case, 10uf/25v.

If it is in fact a capacitor, then the IC appears to be configured as an opamp voltage follower (or buffer).

A single opamp stage, e.g. a single stage of an LM324 or LM2904, would need only five pins: +V, GND, Inverting input, Non-inverting input, and Output.

So, the input PWM signal would be integrated by the 10K resistor and 10uF cap to derive its average DC value.

The opamp, having its inverting input connected to its output, would buffer the integrated signal to provide a low-impedance output.

The only component in the schematic that doesn't make sense is the 2.5uF cap between +5V and the non-inverting opamp input. Is this cap possibly connected between +5v and GND instead (to act as a supply filter)?
picvrss
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Re: Help identify IC and diode

Post by picvrss »

Just another thought: if the SMA 10/25V is a diode, then it would remove any input voltage below ground, and the input PWM signal would then be integrated by the 2.5uF cap to +5V rather than to ground.
It would make no difference to the opamp, though. It would still buffer with a low output impedance.
pman92
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Re: Help identify IC and diode

Post by pman92 »

That would make perfect sense for what it should be trying to achieve, a low impendance output so the exact voltage is delivered to the PCM to spoof it's input.

It could very well be a capacitor. Maybe I should remove it and see. I tried measuring them with verniers, and all the dimensions of the IC I found online are spot on for SOT25. What I thought was a diode was a bit off but I assumed it was close enough. Maybe it's actually a different package?

The 2.5uF capacitor is a ceramic type with no markings. I removed it and measured it with my multimeter and it said approx 2.5uF, which makes sense as it's physically much larger than the other ceramic capacitors in the nF range. I've just double checked and it's definitely connected between the 5v supply and input coming from the microcontroller as in the picture.

Thanks heaps!
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pman92
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Re: Help identify IC and diode

Post by pman92 »

You were on the money. I posted elsewhere and also got told it's a capacitor. The IC is a microchip MCP6001 opamp.

Thanks
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picvrss
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Re: Help identify IC and diode

Post by picvrss »

OK, good to know. The MPC6001 has rail-to-rail outputs and a common-mode input voltage range that exceeds the supply voltage. These would allow it to accept a 0% to 100% duty cycle PWM input range for a full 0v - 5v output. Sure beats a lowly LM324 or LM2904!
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Re: Help identify IC and diode

Post by bf6379 »

With the "10 25V" device being a capacitor, it looks like a standard basic PWM-to-DC converter circuit. The only thing that doesn't make sense is the 2.5uF capacitor.
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