Example = a typical value of R is 50 Ohm and the C value for a SG01S photodiode is 15 pF. This calculates:
with R = internal resistance of the amplifier and C = capacitance of the photodiode
tr/f = 2Pi * 50 Ohm * 21 * 10-12 F = 6.59 * 10-9 s = 6.59 ns
tr = 2Pi
Isat = VOC / RS
A typical value (SiC photodiode) for VOC is 2.0 V and for RS = 5 Ohm. This calculates: Isat = 2.0 V / 5 Ohm = 0.4 A = 400 mA.
The saturation radiant intensity z calculates by the below formula: z = Isat / (S * A)
Where S is the radiant sensitivity of a photodiode and A is the active area. A typical value for S is 0.13 A/W and A = 0.06 mm² (valid for SG01S). This calculates: zsat = 0.4 A / (0.130 A/W * 6 * 10-8 m² ) = 51.28 MW/m² = 5.13 kW/cm²
Detailed further information is provided by the Hamamatsu „Chapter 2 of Handbook of Si Photodiodes“ to be downloaded from the Hamamatsu website.
AMPLIFIED UV PHOTODIODES (TOCON series)
However, one very important point needs to be considered: The TOCON must never saturate while illuminated with UV radiation. Saturation means that the TOCON’s output voltage Vout equals to the power supply voltage Vin. Saturation will not damage the TOCON but means the output voltage is no longer proportional to the radiation to be measured.
This information is quite important for developers who purchase a certain sample quantity or just one TOCON and consider to order a volume quantity. To make sure that not a single TOCON of this volume quantity will saturate in use you should make sure that the sample(s) do not output a voltage higher than 50% of the input voltage while illuminated with the maximum radiation to be measured (e.g. the radiation of a new lamp). If Vout is higher than half of Vin one may try to increase the distance to the UV source or to purchase a less sensitive TOCON (see table below).
This +-20% scatter per class is a default value, and you should prepare your surrounding circuitry to handle TOCONs of several classes. If this causes problems, please contact us. By means of binning processes we feel able to reduce the scatter of the batch. However, please consider that also a reduced scatter still requires an individual calibration of each TOCON. Thus, usually scatter reduction does not create a technical benefit.
The TOCON is stable for capacitive loads up to 30 pF under all circumstances. If more capacitive loading can not be avoided a series resistor of 10 Ohms … 100 Ohms may be required to ensure stability up to few hundred nF.
As-delivered the TOCON is sensitive in the specified range. Example: A TOCON_ABC6 is sensitive between 180 nW/cm² and 1.8 mW/cm².
This means that the TOCON will saturate (output voltage = input voltage) at approx. 1.8 mW/cm². At the lower end a radiation of 180 nW/cm² will still output a couple of mV. While selecting a TOCON, the most important thing to consider is to not illuminate the TOCON until saturation level. A saturation will not damage the TOCON but likely the voltage output will no longer be linear to the radiation input because any increase of radiation above / below the saturation point will not further increase the output voltage.
DATALOGGER, DISPLAYS and CONTROLLER
A typical calibration certificate is given here (link). It contains the following information et al:
– Reference irradiation measured by a traceable-calibrated (spectro-) radiometer
– Calibration object signal
– Calibration factor [Signal]/[W/m²]
200 – 249 nm 13%
250 – 299 nm 7%
300 – 399 nm 5%
400 – 430 nm 4%