IR detector basics

[Nora]

Hello- 4 Questions
Some IR transistors (detectors) come with 2 leads, some with 3.

1. How do I hook up the 3rd lead (which I assume is the base) in this case?
For example, this datasheet doesn't come with a wiring suggestion:

2. Is having one with 3 leads better?

3. Why are the majority/maybe all(?) of them NPN?

4. If I want to shine the IR transmitter/LED continuously and send a signal when I disrupt the beam, is it OK to shine continuously? I'm asking because it seems like most people pulse it at 38kHz. I read this on one site: pulsing at 38kHz ... makes this setup much less prone to interference from sunlight and other sources of infrared radiation

I am not building a TV remote, just a circuit that sends a signal when the beam is interrupted.

Thank you,
Nora

 

[ronsimpson]

Hello- 4 Questions
Some IR transistors (detectors) come with 2 leads, some with 3.

1. How do I hook up the 3rd lead (which I assume is the base) in this case?
For example, this datasheet doesn't come with a wiring suggestion:

Do not connect the base. (B)

2. Is having one with 3 leads better?

The transistor give current gain.

3. Why are the majority/maybe all(?) of them NPN?

I don't know 100%, but I believe NPN transistors are easier to bild

4. If I want to shine the IR transmitter/LED continuously and send a signal when I disrupt the beam, is it OK to shine continuously? I'm asking because it seems like most people pulse it at 38kHz. I read this on one site: pulsing at 38kHz ... makes this setup much less prone to interference from sunlight and other sources of infrared radiation

On the receiving side, looking for 38khz and blocking all other frequencies, really helps with 'noise' from sunlight and lights. If the distance is short it does not matter.

I am not building a TV remote, just a circuit that sends a signal when the beam is interrupted.

Thank you,
Nora

 

[crutschow]

You can add a resistor from the IR detector transistor base to emitter to increase it's operating speed (at the expense of reduced sensitivity) since the resistor will reduce the effect of the miller (collector-base) capacitance of the transistor.

 

[ronsimpson]

You can add a resistor from the IR detector transistor base to emitter to increase it's operating speed (at the expense of reduced sensitivity) since the resistor will reduce the effect of the miller (collector-base) capacitance of the transistor.

Post deleted

 

[Nora]

thank you!
N_N