Simulate LED in LTSpice

[Dr Mitch]

How can I tell if an LED is on or off in Spice model? Currently, I'm
looking at the current and voltage drop, (~20mA and ~1.7V
respectively) but when I do this design with an actual circuit, I get
bupkis.

 

[Helmut Sennewald]

How can I tell if an LED is on or off in Spice model? Currently, I'm
looking at the current and voltage drop, (~20mA and ~1.7V
respectively) but when I do this design with an actual circuit, I get
bupkis.

Hello,

You don't tell SPICE when a diode is on or off, you only specify model
parameters.

Example.for a model specification of a LED with 20mA, 1.7V.

..model LED1 D(Is=1e-19 N=1.6 Rs=2.5 Eg=2.1)

Replace the value D of your diode in the schematic with LED1 and
place the model specifications on your schematic as a SPICE-directive.

I recommend to read some text about the basics of SPICE.

Best regards,
Helmut

 

[Martin]

How can I tell if an LED is on or off in Spice model? Currently, I'm
looking at the current and voltage drop, (~20mA and ~1.7V
respectively) but when I do this design with an actual circuit, I get
bupkis.

Most likely you have miswired your actual circuit (LED wrong way
around perhaps)

Also, LEDs are very long lasting when operated within their allowable
parameters, but if you miswire and subject the LED to excessive
current or reverse voltage, you can destroy it in much less than a
second. If you did that previously, it will most likely look like an
open (infintitely high resistance) to the rest of the circuit now.

 

[Helmut Sennewald]

Hello,

You don't tell SPICE when a diode is on or off, you only specify model
parameters.

Hello again,

Maybe I haven't correctly understood all questions when I answered first.

Just probe the current flowing through the LED in LTspice to see
whether it's "on" or "off". If a few milli-Amperes will be shown,
the LED will light in a real circuit.

Best regards,
Helmut

 

[D from BC]

How can I tell if an LED is on or off in Spice model? Currently, I'm
looking at the current and voltage drop, (~20mA and ~1.7V
respectively) but when I do this design with an actual circuit, I get
bupkis.

Nahhh..It can't be...I hope you don't expect to see the LED symbol to
actually light up?


D from BC