28
\$\begingroup\$

On a transient voltage suppressor, let's take a unidirectional Fairchild P6KE11A for example, what is the main difference between reverse stand off voltage (\$V_{RWM}\$) and breakdown voltage (\$V_{BR}\$) as shown on the chart on page 2?

In my experiments with this part in reverse bias, it begins to conduct just at 10.65V. This is within the \$V_{BR}\$ range of 10.5 to 11.6. I think I understand that the \$V_{BR}\$ range is what I might expect from one particular P6KE11A to another, but of what use is the reverse stand off voltage?

\$\endgroup\$

2 Answers 2

Reset to default
24
\$\begingroup\$

According to this

"Maximum reverse standoff voltage: the voltage below which no significant conduction occurs" "Breakdown voltage: the voltage at which some specified and significant conduction occurs"

This appnote explains

"The TVS breakdown voltage is usually 10 % above the reverse standoff voltage (VR)..."

\$\endgroup\$
2
  • \$\begingroup\$ Thanks BobT, I didn't think to check Wikipedia for the finer details of an electronic part. :) \$\endgroup\$
    – JYelton
    Jan 13, 2013 at 5:18
  • 1
    \$\begingroup\$ Good place to start... I always look for additional corroborating evidence though... \$\endgroup\$
    – BobT
    Jan 13, 2013 at 13:39
3
\$\begingroup\$

VRWM is the Reverse Working Voltage, the voltage a curcuit works with (e.g. 3.3 V or 5 V for microcontrollers). At this voltage, the TVS diode should have no effect on the circuit.

VBR is the Breakdown Voltage at which it starts conducting higher currents. This voltage should be higher than the maximum voltage which the power supply would supply under normal conditions, as otherwise the TVS would constantly be conducting, which it is not designed for.

Additionally, VC is the Maximum Clamping Voltage which is the maximum voltage drop observed over the TVS diode, measured at its peak clamping current IPP. Voltage drop typically rises with higher temperature and higher voltage over the TVS.

For a transient voltage, the clamped voltage would e.g. look as the black line in the drawing. It is not flat as often drawn as simplified version.

TVS Clamping

because … the diode does not suddenly allow ∞ A after the voltage passes VBR.

enter image description here

References

The following application notes contain more detailed information:

\$\endgroup\$
2
  • \$\begingroup\$ Could you explain the two plots of "Zener" and "TVS"? AFAIK, the only reason a zener/avalanche type TVS has looser tolerances is, precisely that i.e. they aren't selected as tightly as zeners are (or rather the common grades of zener are a few percent, not a raw 5 or 10% as TVSs might); and because TVSs are tested to much higher peak currents (i.e. the I scales of the two curves would be different by orders of magnitude). With equal scaling, I would expect an MOV to look somewhat like the "TVS" curve as shown. \$\endgroup\$
    – Tim Williams
    Jun 15 at 0:57
  • \$\begingroup\$ I unfortunately don't have more resources on that other than AN1142 (third page), they do not give a physical background, only that normal Zeners and Zener TVS are optimised for different purposes (peak pulse vs accurate voltage). \$\endgroup\$
    – Simon A. Eugster
    Jun 15 at 5:46

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.