What are the key features of the BPW21R?
The BPW21R is a planar silicon PN photodiode housed in a hermetically sealed short TO-5 metal case with a flat glass window. Its most distinctive feature is a built-in color correction filter that gives it a spectral response closely matching that of the human eye, with peak sensitivity at 565nm (green light). The device offers a radiant sensitive area of 7.5mm², high photo sensitivity (9nA per lux), an angle of half sensitivity of ±50°, and exceptionally low dark current (typically 2nA). Due to its extremely high dark resistance, the short-circuit photocurrent remains linear across seven decades of illumination levels, while the open-circuit voltage shows a strictly logarithmic correlation over the same range. The device is RoHS compliant, operates over a temperature range of -40°C to +125°C, and has a maximum reverse voltage rating of 10V.
What is the BPW21R used for?
The BPW21R is specifically designed for high-precision linear applications and color measurement purposes. Typical applications include light sensors in cameras, photometers (light meters), color analyzers, exposure meters, and other general medical and industrial measurement and control systems. Its human-eye-matched spectral response makes it particularly well-suited for ambient light sensing, optical sensing in consumer electronics, environmental monitoring equipment, industrial automation systems, and agricultural technology where accurate visible light measurement is required.
Are there any alternative parts for the BPW21R?
Yes, several alternative photodiodes can serve as replacements, though designers should always verify compatibility with their specific circuit requirements. Within the Vishay family, the **BPW21** is the most direct alternative, offering similar silicon photodiode characteristics with comparable spectral sensitivity. Other manufacturers provide functional alternatives, including **Osram SFH 203 P** (known for its photodetector capabilities), **Everlight PD204-6C**, and **Excelitas VTB8441BH** (provides similar photodetection performance). Additional possible alternatives include **BPW34**, **BPW24R**, and **BPW17N**, though these may have different package styles or active area sizes. When selecting an alternative, key parameters to compare include peak wavelength sensitivity (565nm for BPW21R), spectral range (420nm to 675nm), dark current, active area size (7.5mm²), and package type (TO-5).
