ITech IT8900 Series - Measurement of Voltage or Current Rise;Fall Time

Function and Features
Copyright © ITECH Electronic Co., Ltd. 39
Calculation method of Vd and R:
Definition:
 Vo: constant working voltage of load LED of LED constant current source;
 Io: output current of LED constant current source;
 Vd: break-over voltage of diode (string);
 R: constant resistance.
V-I curve of LED is as shown below.
According to four parameters above and the V-I curve of LED, you can calculate
the value of R and Vd.
12
12
II
VV
R
−
−
=
( )
RIVV ×−=
0od
Note
The value of V2, V1, I2 and I1 should be close to the static working point of LED as shown
in the red circle above.
Or you can calculate the value of R and Vd by the following method.
Vd =V*0.8 R=0.2V/I
Where:
 V: constant working voltage of load LED of LED constant current source;
 I: output current of LED constant current source;
 Vd: break-over voltage of diode (string);
 R: constant resistance.
In the example: Vd=50V*0.8=40V R=(0.2*50V)/0.2A=50Ω.
3.14 Measurement of voltage or current rise/fall time
The IT8900 series electronic load is provided with special voltage or current
rise/fall time measurement function. This function gives a simple analog of
voltage or current rise/fall speed of oscilloscope test power.