Application Note

VISHAY SEMICONDUCTORS
Zener and Suppressor Diodes
Application Note
Temperature Dependency of Zener Voltage
External warm up
phase
Internal warm up phase
46.0 V
45.5 V
Thermal coupling:
Diode position between the
heat sinks
Iz
A
B
C
Vz
A
45.0 V
Thermal
Equilibrium
pulsed
D
44.5 V
Iz = 10mA
B
Zener Voltage
44.0 V
A
B
C
D
C
43.5 V
Iz = 5mA
D
43.0 V
42.5 V
A
B
C
D
Iz = 1mA
42.0 V
41.5 V
TAmbient (heat sink) = 25°C
41.0 V
0.00001 s
0.0001 s
0.001 s
0.01 s
0.1 s
1s
10 s
100 s
Pulse duraon
22268
Fig. 1 - Zener Voltage Change vs. Pulse Duration
Phase 1: Internal warm up phase
The current starts to heat the silicon of the p/n junction and charge the caloric capacitance of the material around the junction.
The heat moves from the warm junction through the silicon chip to the metal contact inside the glass package to the terminals
of the wire. With the rising temperature, the Zener voltage increases according to the temperature coefficient (TC).
Document Number: 84810
Revision: 01-Oct-10
For technical questions within your region, please contact one of the following:
DiodesAmericas@vishay.com, DiodesAsia@vishay.com, DiodesEurope@vishay.com
www.vishay.com
1
APPLICATION NOTE
The Zener voltage (VZ) of a Zener or avalanche diode depends on the diode’s junction temperature.
Any current running through the p/n junction barrier generates the electrical power of: P = IZ * VZ
This electrical power is equivalent to the thermal power applied to this junction. Depending on the duration and the intensity of
the current, the applied thermal energy increases and heats the junction. The upper diagram shows the Zener voltage change
of a BZX85C43 Z-Diode in a DO-41 wired glass package during a constant current pulse. The diode is mounted between large
heat sinks (copper blocks) with a stable temperature of 25 °C.
Application Note
Vishay Semiconductors
Temperature Dependency of Zener Voltage
Phase 2: External warm up phase
The heat leaves the package and moves through the wires to the heat sink. In contrast to phase 1, during phase 2 thermal
resistance can be influenced by the customer. The shorter the wires, the lower the additional thermal resistance to the heat sink
with defined low temperature and vice versa.
Phase 3: The thermal equilibrium
The material along the following thermal path from the junction to the heat sink is now completely charged up; the junction
temperature and thus the Zener voltage are now stabilized.
The diagram shows that the test conditions are important in defining the Zener voltage of a Zener diode:
• the Zener test current IZ
• the junction temperature right before the pulse test
• the point in time during the current pulse at which the voltage is measured
APPLICATION NOTE
• the junction-to-ambient thermal resistance.
Document Number: 84810
Revision: 01-Oct-10
For technical questions within your region, please contact one of the following:
DiodesAmericas@vishay.com, DiodesAsia@vishay.com, DiodesEurope@vishay.com
www.vishay.com
2