LM124AQML-SP: 5962R9950402VDA

Hi Isaac,

what do you mean by "reverse current"?

Kai

I have conected a photodiode. It is possible that when Vcc=0 and the photodiode recieve light can be to generate a small current so I need to know "the reverse current" of each inputs and outputs of LM124.

Hello Kirby.

I don't mean leakage current, I mean the reverse current or limit protection in the inputs or outputs because I have connected a photodiode and can work as a photovoltaic cell.

Thanks

Hi Isaac,

there are several ways to run a photodiode in combination with an OPAmp, the photovoltaic mode with a TIA (zero bias and non zero bias), the photoconductive mode and others.

Can you show us a schematic?

Kai

Hi Isaac,

I am still not sure I understand your question.  

See the schematic in the datasheet.  The inputs and outputs are relatively large, high breakdown pnp transistors that are mostly isolated and there are no ESD cells on the part.

The inputs bias current is independent of Vcc as long as the input voltage does not violate abs max.   The outputs will be independent of Vcc, other than output current.  Obviously, with Vcc = 0, the part will not be able to supply current.

Hi Kai.

Ok, I think the current is insignificant, but we want sure how much is.

Please, you can find attached our schematic.

Ok Kirby, We will see the abs max ratings.
Thank you.

Hi Isaac,

when the photodiode becomes irradiated while the OPAmp isn't powered, the cathode goes negative for some 100mV and a current begins to flow from the cathode to the anode of photodiode. The photodiode works like a little battery where also the current flows internally from the -pole (=cathode) to the +pole (=anode). If the irradiation is very high and the photodiode is "powerful" enough, the -input of LM124 could go so much negative (<-0.3V), that a current can flow out of the -input of LM124. This current is critical and must be limited to 50mA, according to the absolute maximum ratings of datasheet of LM124.

One remedy is to put a small current Schottky diode with little junction capacitance, like the BAT54 for instance, in parallel to the photodiode. Or you can limit the current flowing out of the -input of LM124 by a small resistor.

In most cases, if the irradiation of photodiode is limited or if the photodiode is not powerful enough, no additional protection circuitry is needed, though, And the output of LM124 should be sufficiently current limited by R1, anyway.

Kai