2.4 Volt Diode vs. 3.6 volt diode

[Aero1207]

Our firm is using a pressure transducer in an application and the circuit design
uses a 2.4 volt diode on the output. We have seen some of the diodes become blown due
to transient spikes. We know that at one point the manufacturer had considered a 3.6 volt diode
on the output. The question of susceptibility came up between the two diodes. Would a 3.6 volt diode be
less susceptible to voltage stresses than a 2.4 volt diode?

 

[MacGyverS2000]

In and of itself, it wouldn't. It will depend upon what the other specs of the diode are, particularly the peak inverse voltage (PIV).

Dan - Owner

http://www.Hi-TecDesigns.com

 

[itsmoked]

There are no 2.4V "diodes" unless you mean Zener Diodes.
Your application sounds rather odd. Why would your device need a Zener on its output? Does your device cause "the spikes"?

Or do you really mean your device's input - supplied by the pressure transducer?

Is the Zener there to protect your circuit from spikes coming in on the pressure transducer leads?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Aero1207]

It is a zener diode and is located between the negative legs for power and output signal.

 

[BrianE22]

If one end is on the negative leg and the other end is pointing to (and connected to) the output then the diode is there to protect the circuit from spikes coming from the output of the transducer. Hard to believe there's enough power in the spikes to blow the zener. Are you sure the transducer isn't putting out a DC voltage greater than 2.4 volts?

 

[itsmoked]

Areo you are not successfully clarifying anything. Nothing you're describing is making any logical sense to sound electronic design. Either the setup is completely screwed up or dabblers are running a'muck. If you want good help you need to provide more clearer information.

How about a schematic or napkin sketch or something useful.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[IRstuff]

Things are often scabbed onto circuits because someone screwed up something and patched it with another thing, rather than fixing it correctly.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529

 

[Aero1207]

Attached is a basic schematic of the transducer. Source of spike causing D1 to blow is not known. Original question
was concerning the susceptibility of a 2.4 zener vs a 3.6. Assume PIV are equivalent. Red is +28v in, green is +5v out.

 

[itsmoked]

Thanks for the schematic. That helps a LOT.

I don't like what I'm seeing here. But aside from that, to answer your question, the susceptibility of damage between the two voltages is not normally a considered issue only that the Zener knee of the part's Voltage/Current curve is mushier on the lower voltage. What blows the diodes since their PIVs are not the thing dying is the current thru them. The power a Zener will have to dissipate is its zener voltage x the current.

So, the current from the white wire heading to the black wire is causing power to be dissipated in the zener. So much that the zener is baking-dead. Adding a higher voltage zener could prevent the burn outs if and only if the voltage difference is higher than 2.4V but lower than 3.6V a condition I suspect is not the case.

I don't see 'noise' or 'spikes' as causing the zener's travails. More like a steady state difference between the BLACK and the WHITE wires. Often these mickey-mouse jury rigs like the zener have issues with power-up or power-down as capacitors are being charged or discharge. If the 'signal conditioner' has a bunch of capacitance then when the 28V supply is shut off that capacitance can raise the WHITE voltage above the BLACK voltage causing the capacitance to discharge thru the zener and frying it.

I'd look at the voltage across the zener during all phases of operation to see what's up; during running, power-on, and power-off periods. If it looks like the zener voltage is reached only during power-off then the scenario I described above is the likely problem. If the zener voltage is always present in all three described cases then you need to cut in an ammeter and see what's going on. If transients are suspected then you tag in a 1 ohm resistor between the top of the zener and the WHITE wire and using a scope grounded only to the WHITE wire and across the resistor you can then watch for fast large current events.

The current is the voltage/resistor. The power being dumped in the zener is that current times the zener voltage. Compare that to the allowed power of that specific zener on its data sheet.

There is also a chance this is about the other things happening on the WHITE wire coming from off to the right. Perhaps those electronics are being powered by the same 28V supply and this dumb zener scheme is being tripped up by it.

Keith Cress
kcress -

http://www.flaminsystems.com