IR detector basics

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

Nora said:

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:

Click to expand...

Do not connect the base. (B)

2. Is having one with 3 leads better?

Click to expand...

The transistor give current gain.

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

Click to expand...

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

Click to expand...

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

Click to expand...

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.

crutschow said:

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.

Click to expand...

Post deleted

thank you!
N_N