How does one find what base current to use in simulating a phototransistor?

I wish to use LTspice to simulating a phototransistor (LPT80), so I downloaded the model but I have not found information on the base current to use?

And how do I relate the base current to daylight?

Is there a better way to know than trial and error? eg -1mA does turn it on and 0A does turn it off.

The model (in "OSRAM Phototransistors II.lib") can be found here https://www.osram.com/apps/downloadcenter/os/?path=%2Fos-files%2FElectrical+Simulation%2FIR%2FSilicon+Photodetectors%2FPSpice+Libraries%2F

The datasheet for LPT80A is:https://www.osram.com/ecat/Radial%20Sidelooker%20LPT%2080%20A/com/en/class_pim_web_catalog_103489/global/prd_pim_device_2219650/#tools

My LTspice LPT80 circuit

  • 1
    \$\begingroup\$ That diagram looks wrong. Shouldn't the current be going into the Base? \$\endgroup\$ Nov 12, 2020 at 3:33
  • \$\begingroup\$ Yes, it is as I'm using negative current. It is just a test circuit. :) \$\endgroup\$
    – Geoff
    Nov 12, 2020 at 6:15
  • \$\begingroup\$ Please link to THE data sheet and not a lib file \$\endgroup\$
    – Andy aka
    Nov 12, 2020 at 9:18
  • \$\begingroup\$ A link to the datasheet has now been added. \$\endgroup\$
    – Geoff
    Nov 12, 2020 at 10:18

1 Answer 1


Photodiodes are typically spec'd at 0.5 amp per watt of photon flux.

So work from that concept.

  • \$\begingroup\$ Interesting, so is that "0.5A" collector emitter current "per watt of photon flux"? Do you have any reference? \$\endgroup\$
    – Geoff
    Nov 12, 2020 at 6:01
  • \$\begingroup\$ Photodiodes don't have collector current. (Reference any photodiode datasheet). Since a phototransistor's base region is the photodiode. take that as 0.5A/watt of base current. \$\endgroup\$ Nov 12, 2020 at 14:39

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