Clear epoxy body · 5.4 × 4.3 mmPIN photodiode chip · light-sensitive area 7.5 mm²Cathode pinAnode pin

Black or clear flat package, wide light window, two legs
BPW34: ≈ 5.4 × 4.3 mm flat body, light area 7.5 mm²

Diodes

Photodiode

In simple terms

What is this?

A small diode that generates electricity when light hits it; the more light, the more current.

What is it for?

Detects light very fast; used for remote control signals and for measuring light intensity.

Where do you see it?

In TV and air conditioner remote-control receivers, and in pulse monitors.

How do you spot it?

A small body with a clear or dark window facing the light, and two legs.

Caution:

It is usually connected in the reverse direction; if you connect it the wrong way it seems not to work.

Technical definition

A diode that produces current when light falls on it. It is usually connected in reverse; the reverse current rises almost linearly with the incoming light. It is much faster than an LDR, so it is used in remote-control receivers and light meters.

ExampleBPW34

Reverse voltagemax. 60 V

Peak sensitivity≈900 nm

Schematic symbol Same in IEC and ANSI

IEC 60617: the drawing style used in Türkiye and Europe.

Pins 2

1Anode (A)Goes to ground in the reverse connectionA

2Cathode (K)Goes to plus in the reverse connection; check the marking in the datasheetK

Features typical

Max. reverse voltage: 60 V
Spectral range: 430–1100 nm
Peak sensitivity: ≈900 nm
Dark current: ≈2 nA (10 V)
Photocurrent: ≈50 µA (1 mW/cm², 5 V)
Rise time: ≈100 ns
Example part: BPW34

Common mistakes

Using it like an LDRA photodiode acts like a current source, not a resistor. Turn the current into voltage with a resistor or an op-amp circuit.

Connecting it in the forward directionFor fast, linear measurement connect it in reverse: cathode to positive. In the forward direction it conducts like a normal diode.

Test with a multimeter

Test whether this part is good with the multimeter on the measurement screen.

Take a measurement

Where it is used

IR remote control receiverLight meterOptical encoder and counterPulse sensor