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Mosfet VP0808L Fails?

Hi,

I am using VP0808L (Mosfet) in my circuit. I am finding that this device fails instantaneously, whenever i change this device with new one (taking antistatic care, use of wrist straps and earthing them, also the work table is antistatic) the circuit works, sometimes even taking antistatic care the Mosfet fails why?. I want to know whether there are any compatible devices to this part which are sturdy enough to handle static currents? And what are the cases related to static currents when such type of devices fails and what care should i take?

Thanks and regards, Nick

Reply to
Nick
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Nick, may I suggest you learn to be more careful? While some small MOSFETs do have gate zeners, most do not. In fact, I've been told by MOSFET manufacturers that when they do have gate zeners, failure of the zener from static damage can become a big problem. So most MOSFETs rely user care, and on their intrinsic gate capacitance for protection. The VP0808L has a gate capacitance Ciss = 75pF typical, at -25V bias, and over 150pF at 0V. This is actually quite high for a small FET; compare it to the popular 2n7000 with Ciss = 22pF. If we can keep from blowing out all our 2n7000s, you should be able to keep from blowing out your VP0808Ls. :-)

Hmm, I wonder if something's wrong with your soldering iron?

--
 Thanks,
    - Win
Reply to
Winfield Hill

It sounds like you can change the MOSFET and things work, then it soon fails (can't be instantaneous or you'd never see your circuit working).

That sounds more like a symptom of a faulty circuit that's taking out MOSFETs rather than static damage going in.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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Reply to
Tim Wescott

The cause of the failure is exactly as obvious as the diagram you posted that shows us your circuit.

Ed

Reply to
ehsjr

Your state that the MOSFET "fails instantaneously" and your circuit works. It must therefore be your goal to distroy MOSFETs. You seem to have no problem achieving this and no reason to ask questions.

Adam

Reply to
Adam S

Hi, I am using a Precision Voltage-To-Current Converter/Transmitter IC XTR110 of Texas Instruments. I am using the same suggested circuit as shown in the datasheet below. FOr input 0-10v and output 0-20mA. Link:

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Thanks And regards, Nick.

Reply to
Nick

No No No. You have either failed to implement the circuit described, or have other circuit/limitations or errors causing the failure.

--
JosephKK
Gegen dummheit kampfen die Gotter Selbst, vergebens.  
--Schiller
Reply to
Joseph2k

The transmitter driver should be sized for VCC x Iout. If this is the

13V minimum of the drawing, the part will be dissipating 260mW. If it goes to the 40V limitation of the IC, that's 800mW.

T0-92 packages may be OK for a while at the low end, you shouldn't expect them to run a long time at the other, even if it's within the parts 25degC operating limits. TO237 ratings are based on case temperature - no ambient. The latter unheatsunk condition generates ratings that are little better than TO-92.

If you've been fiddling with the span adjust pins, then you'd have to recalculate accordingly. Does it die doing 4mA? 16mA?

Long traces on the gates of smaller mosfets attract disaster without series resistor current and shunt diode voltage limiters.

Gate failures are readily diagnosed by a simple resistance check, at any time with power off, even while soldering. With the soldering iron grounded, any charge stored in the body of your floating transmitter circuit will likely want to use the path.

Mind you, a low gate impedance is not automatically an indication that damage has occurred through this terminal.

RL

Reply to
legg

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