ST STEVAL-SCR002V1, User Manual

Page: 13 / 28

5 Thermal management
For a safe and reliable operation, it is important to keep the junction temperature of the SCR below its maximum
junction temperature. The
STEVAL-SCR002V1 uses two high temperature TN1605H-6T SCRs that can operate at
up to 150°C.
To calculate the junction temperature, you need to know the ambient temperature or the case temperature, the
dissipated power, and the thermal resistance.
5.1 Dissipated power
Current alternatively flows through the two SCRs. The figure below shows the current waveform in a single SCR.
Figure 19. SCR current waveform
Referring to AN533 , the dissipated power corresponding to this half wave can be calculated as follows:
Pdis = VTO × IT av + RD × ITRMS
2
where:
IT av =
IP
π
and
ITRMS =
IP
2
V
TO
and R
D
, respectively, correspond to the threshold voltage and the dynamic resistance.
The following tables are extracts from the TN1605H-6T data sheet.
Table 2. Static electrical characteristics
Symbol Test conditions
T
j
Value Unit
V
TO
On-state threshold voltage 150°C max. 0.82 V
R
D
Dynamic resistance 150°C max. 25 mΩ
Table 3. Thermal resistance
Symbol Parameter Value Unit
R
th(j-c)
Junction to case (DC) 1.1
°C/W
R
th(j-a)
Junction to ambient (DC) 60
The junction temperature can then be calculated as shown below.
UM2948
Thermal management
UM2948 - Rev 1
page 13/28