Effectiveness of p6ke39ca clamping diode

[REng]

Hey all,

I need to clamp a transient voltage (around 5-10 us) which can rise up
to 20V +ve and 20 V -ve i.e. 40 V pp to +/- 5V. The frequency of this
voltage varies from 10 to 15 MHz.

I was thinking of the p6ke39ca bi-directional diodes to clamp this
voltage. One end of the diodes would be connected to the signal and the
other ends would be connected to +5 and -5 V respectively as seen below


---|----|------> signal
| |
D D
| |
| |
+5V -5V

The maximum current in the system is 2A. My question is: would this be
an effective scheme and would this need multiple diodes for operation ?

 

[Rene Tschaggelar]

REng wrote:

Hey all,

I need to clamp a transient voltage (around 5-10 us) which can rise up
to 20V +ve and 20 V -ve i.e. 40 V pp to +/- 5V. The frequency of this
voltage varies from 10 to 15 MHz.

I was thinking of the p6ke39ca bi-directional diodes to clamp this
voltage. One end of the diodes would be connected to the signal and the
other ends would be connected to +5 and -5 V respectively as seen below


---|----|------> signal
| |
D D
| |
| |
+5V -5V

The maximum current in the system is 2A. My question is: would this be
an effective scheme and would this need multiple diodes for operation ?

A series resistor for the signal might limit the current ...

Rene

 

[Rich Grise]

On Wed, 05 Jan 2005 09:01:26 -0800, REng wrote:

Hey all,

I need to clamp a transient voltage (around 5-10 us) which can rise up
to 20V +ve and 20 V -ve i.e. 40 V pp to +/- 5V. The frequency of this
voltage varies from 10 to 15 MHz.

I was thinking of the p6ke39ca bi-directional diodes to clamp this
voltage. One end of the diodes would be connected to the signal and the
other ends would be connected to +5 and -5 V respectively as seen below


---|----|------> signal
| |
D D
| |
| |
+5V -5V

The maximum current in the system is 2A. My question is: would this be
an effective scheme and would this need multiple diodes for operation ?

This isn't the typical way you'd use a transzorb.

In your circuit, just use ordinary diodes, say, 1N4148 or 1N914, with the
obvious polarity.

Good Luck!
Rich

 

[Roger Lascelles]

"Rich Grise" <richgrise@example.net> wrote in message
newsan.2005.01.05.20.55.09.96165@example.net...

On Wed, 05 Jan 2005 09:01:26 -0800, REng wrote:

This isn't the typical way you'd use a transzorb.

In your circuit, just use ordinary diodes, say, 1N4148 or 1N914, with the
obvious polarity.

I think respondents are having trouble working out how to help you, because
you have stripped down the problem and the big picture is lost.

Can you tell us what produces the signal ?

Where is the signal going to ?

Do you want to measure the signal voltage, or is the signal going to a power
absorbing load ?

What produces the transients. Are the transients periodic or rare events ?


The p6ke39ca transient suppressor diodes can handle 5 watts average power.
If you exceed this, you will cook the diodes. The diodes are basically
zeners with a high peak power capability compared with average power. They
are very fast.

The plus and minus supplies you show can get current pumped into them - in
some circumstances, this can "pump up" the supply voltage. This is why
generally, you put a bidirectional diode to ground and the diode clamps in
both directions.

Roger

 

[JeffM]

MAXIM MAX366 and MAX367
REng

As Bob Baer so often reminds us
**Is there anything more than datasheets available
for this Maxim part?**
http://groups-beta.google.com/group/sci.electronics.design/search?q=Robert-Baer+Maxim&scoring=d

 

[REng]

All,
I found something else that I thought might help me. They are the
MAXIM MAX366 and MAX367 multiple, two-terminal circuit protectors.

More info about them is in here:
http://pdfserv.maxim-ic.com/en/ds/MAX366-MAX367.pdf

---i have pasted the intro part of the datasheet below---

Placed in series with signal lines, each two-terminal
device guards sensitive circuit components against
voltages near and beyond the normal supply voltages.
These devices are used at interfaces where sensitive circuits
are connected to the external world and could
encounter damaging voltages (up to 35V beyond the supply
rails) during power-up, power-down, or fault conditions.
The MAX366 contains three independent protectors and
the MAX367 contains eight. They can protect analog signals
using either unipolar (4.5V to 36V) or bipolar (ą2.25V
to ą18V) power supplies. Each protector is symmetrical.
Input and output terminals may be freely interchanged.
These devices are voltage-sensitive MOSFET transistor
arrays that are normally on when power is applied and
normally open circuit when power is off. With ą10V supplies,
on-resistance is 100˝ max and leakage is less than
1nA at +25°C.
When signal voltages exceed or are within approximately
1.5V of either power-supply voltage (including when
power is off), the two-terminal resistance increases dramatically,
limiting fault current as well as output voltage to
sensitive circuits. The protected side of the switch maintains
the correct polarity and clamps approximately 1.5V
below the supply rail. There are no "glitches" or polarity
reversals going into or coming out of a fault condition.