0
\$\begingroup\$

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

\$\endgroup\$
4
  • 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

1
\$\begingroup\$

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

So work from that concept.

\$\endgroup\$
2
  • \$\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

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.