AN4451

How does the UV sensor work

DocID025985 Rev 1

3/15

I_Uv

+

-

Vcc

Rf

Vout

Cf

Uv sensor

ADC

Rn

Cn

STM32 microcontroller

1

How does the UV sensor work

A UV sensor works as a photodiode. When a UV source irradiates the sensor, UV radiation

is converted into a small current proportional to the UV radiation. Obviously, the delivered

current depends on the UV sensor used. Formula (1) shows a rough estimation of the

photocurrent (Ip) given for a particular active chip area (AChip).

where:

Achip is the active chip area in m

2

Schip is the chip’s spectral sensitivity in AW

-1

1.1

Signal conditioning of the UV sensor

The UV sensor generates a small current, generally a few nA, which is proportional to the

UV insulation. Figure 1 exhibits a transimpedance amplifier configuration that is used to

convert this current into an adequate voltage that can be read by the ADC of the

microcontroller.

Figure 1: Transimpedance amplifier

The op-amp converts the current generated by the sensor into a voltage thanks to the Rf

resistor. The output voltage sensed by the ADC is theoretically given in formula (2):