SMBJ12AON Datasheet, PDF (4/6 Pages) ON Semiconductor – 600 Watt Peak Power Zener Transient Voltage Suppressor

SMBJ12AON
APPLICATION NOTES
RESPONSE TIME
In most applications, the transient suppressor device is
placed in parallel with the equipment or component to be
protected. In this situation, there is a time delay associated
with the capacitance of the device and an overshoot
condition associated with the inductance of the device and
the inductance of the connection method. The capacitive
effect is of minor importance in the parallel protection
scheme because it only produces a time delay in the
transition from the operating voltage to the clamp voltage as
shown in Figure 5.
The inductive effects in the device are due to actual
turn-on time (time required for the device to go from zero
current to full current) and lead inductance. This inductive
effect produces an overshoot in the voltage across the
equipment or component being protected as shown in
Figure 6. Minimizing this overshoot is very important in the
application, since the main purpose for adding a transient
suppressor is to clamp voltage spikes. The SMB series have
a very good response time, typically < 1 ns and negligible
inductance. However, external inductive effects could
produce unacceptable overshoot. Proper circuit layout,
minimum lead lengths and placing the suppressor device as
close as possible to the equipment or components to be
protected will minimize this overshoot.
Some input impedance represented by Z_in is essential to
prevent overstress of the protection device. This impedance
should be as high as possible, without restricting the circuit
operation.
DUTY CYCLE DERATING
If the duty cycle increases, the peak power must be
reduced as indicated by the curves of Figure 7. Average
power must be derated as the lead or ambient temperature
rises above 25°C. The average power derating curve
normally given on data sheets may be normalized and used
for this purpose.
OVERSHOOT DUE TO
V_in (TRANSIENT)
V
V_in (TRANSIENT)
V _{INDUCTIVE EFFECTS}
V_L
V_L
V_in
t_d
t_D = TIME DELAY DUE TO CAPACITIVE EFFECT
t
t
Figure 5.
Figure 6.
1
0.7
0.5
0.3
0.2
0.1
0.07
0.05
0.03
0.02
0.01
0.1 0.2
PULSE WIDTH
10 ms
1 ms
100 ms
10 ms
0.5 1 2
5 10 20
D, DUTY CYCLE (%)
50 100
Figure 7. Typical Derating Factor for Duty Cycle
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