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# LM2904：LM2904

Part Number: LM2904
Other Parts Discussed in Thread: TL071H, TL081H

R1=R3=1.1K

R2=R4= 100K

vo 理論上會是多少呢?

我從電表或示波器上看到都在12.8~13.3 v 這是合理的嗎？　還是已經進入飽和呢？

• Hello Angust, welcome to the English e2e forums.

LM2904 is not a rail to rail input, so LM2904 supply must be greater than supply used for input. Supply for LM2904 needs to be at least 2V higher than input common mode voltage.

Expect a lot of issues from the resistor accuracies; this can turn your high voltage common mode voltage into an output voltage.

If the sense voltage isn't much bigger than the LM2904 input offset error, then expect a lot of error from that too.

So what is the range of sense current or voltage?

• Hi ROn,

Current detection range 0~8A max: 8A

Does the OP have any suggestions?

• Angus

I suggest TL071H or TL081H as the current sense amplifier. The Vos is 5mV over temperature so expect up to +/-333mA of offset error. Using a larger R1 or picking a better offset op amp can improves this. Gain error should match resistor tolerances. The two that matter are R2, R3

Using a PMOS to output a current and only having two critical resistors makes this circuit have a good supply rejection. VOUT needs a buffer unless the destination is high impedance.

• Angus,

VOUT = VR1 * (R2 / R3) + Vos (1 + R2/R3)