Forums

zener diode pulse current rating

Started by panfilero April 20, 2012
I need a 30V zener to drop the a high voltage of 100V down to 60V so I
can use it with a switch mode power supply chip.  So while this
circuit is in use the zener will be exposed to current pulses from the
switching, these current pulses are in the neighborhood of 1A.  I've
gone to digikey and pulled up some zeners but I don't see this rating,
where can I find the rating that tells me whether or not it's ok to
pulse 1A through my zener?

here's the one I'm looking at

http://www.nxp.com/documents/data_sheet/NZX_SER.pdf


much thanks!
On Apr 20, 3:36=A0pm, panfilero <panfil...@gmail.com> wrote:
> I need a 30V zener to drop the a high voltage of 100V down to 60V so I > can use it with a switch mode power supply chip. =A0So while this > circuit is in use the zener will be exposed to current pulses from the > switching, these current pulses are in the neighborhood of 1A. =A0I've > gone to digikey and pulled up some zeners but I don't see this rating, > where can I find the rating that tells me whether or not it's ok to > pulse 1A through my zener? > > here's the one I'm looking at > > http://www.nxp.com/documents/data_sheet/NZX_SER.pdf > > much thanks!
I'm guessing it's in the power rating, if it's a 30V zener, and has a power rating of 500mW, then max current is I =3D .5/30 =3D 17mA.... weak! but this doesn't tell me about current pulses...spikes...
On 04/20/2012 03:44 PM, panfilero wrote:
> On Apr 20, 3:36 pm, panfilero<panfil...@gmail.com> wrote: >> I need a 30V zener to drop the a high voltage of 100V down to 60V so I >> can use it with a switch mode power supply chip. So while this >> circuit is in use the zener will be exposed to current pulses from the >> switching, these current pulses are in the neighborhood of 1A. I've >> gone to digikey and pulled up some zeners but I don't see this rating, >> where can I find the rating that tells me whether or not it's ok to >> pulse 1A through my zener? >> >> here's the one I'm looking at >> >> http://www.nxp.com/documents/data_sheet/NZX_SER.pdf >> >> much thanks! > > I'm guessing it's in the power rating, if it's a 30V zener, and has a > power rating of 500mW, then max current is I = .5/30 = 17mA.... weak! > but this doesn't tell me about current pulses...spikes...
I dunno, but if you are dropping 100V to 60V with a 30V zener, that leaves about 10V of "smoke" to dispose of...:-) bill
On Apr 20, 5:46=A0pm, Bill Martin <w...@wwmartin.net> wrote:
> On 04/20/2012 03:44 PM, panfilero wrote: > > > > > > > > > > > On Apr 20, 3:36 pm, panfilero<panfil...@gmail.com> =A0wrote: > >> I need a 30V zener to drop the a high voltage of 100V down to 60V so I > >> can use it with a switch mode power supply chip. =A0So while this > >> circuit is in use the zener will be exposed to current pulses from the > >> switching, these current pulses are in the neighborhood of 1A. =A0I've > >> gone to digikey and pulled up some zeners but I don't see this rating, > >> where can I find the rating that tells me whether or not it's ok to > >> pulse 1A through my zener? > > >> here's the one I'm looking at > > >>http://www.nxp.com/documents/data_sheet/NZX_SER.pdf > > >> much thanks! > > > I'm guessing it's in the power rating, if it's a 30V zener, and has a > > power rating of 500mW, then max current is I =3D .5/30 =3D 17mA.... wea=
k!
> > but this doesn't tell me about current pulses...spikes... > > I dunno, but if you are dropping 100V to 60V with a 30V zener, that > leaves about 10V of "smoke" to dispose of...:-) > > bill
good point.... let's say for this thread 100 =3D 90
On 4/20/2012 1:36 PM, panfilero wrote:
> I need a 30V zener to drop the a high voltage of 100V down to 60V so I > can use it with a switch mode power supply chip. So while this > circuit is in use the zener will be exposed to current pulses from the > switching, these current pulses are in the neighborhood of 1A. I've > gone to digikey and pulled up some zeners but I don't see this rating, > where can I find the rating that tells me whether or not it's ok to > pulse 1A through my zener? > > here's the one I'm looking at > > http://www.nxp.com/documents/data_sheet/NZX_SER.pdf > > > much thanks!
You're asking for trouble. If your average current is within the zener rating, you can fix that with a cap...but then you have to worry about the turn-on transient current thru the zener to charge the cap. Look at the thermal time constant graphs and put in your unspecified pulse durations. Put an emitter follower after the zener.
panfilero wrote:

> On Apr 20, 5:46 pm, Bill Martin <w...@wwmartin.net> wrote: > >>On 04/20/2012 03:44 PM, panfilero wrote: >> >> >> >> >> >> >> >> >> >> >>>On Apr 20, 3:36 pm, panfilero<panfil...@gmail.com> wrote: >>> >>>>I need a 30V zener to drop the a high voltage of 100V down to 60V so I >>>>can use it with a switch mode power supply chip. So while this >>>>circuit is in use the zener will be exposed to current pulses from the >>>>switching, these current pulses are in the neighborhood of 1A. I've >>>>gone to digikey and pulled up some zeners but I don't see this rating, >>>>where can I find the rating that tells me whether or not it's ok to >>>>pulse 1A through my zener? >> >>>>here's the one I'm looking at >> >>>>http://www.nxp.com/documents/data_sheet/NZX_SER.pdf >> >>>>much thanks! >> >>>I'm guessing it's in the power rating, if it's a 30V zener, and has a >>>power rating of 500mW, then max current is I = .5/30 = 17mA.... weak! >>>but this doesn't tell me about current pulses...spikes... >> >>I dunno, but if you are dropping 100V to 60V with a 30V zener, that >>leaves about 10V of "smoke" to dispose of...:-) >> >>bill > > > good point.... let's say for this thread 100 = 90
why not simply use a transistor to boost the handling of the zener circuit? Cathode equal + | | +---+-----+------------------------+ | | | + | | z | | zener diode A | | + + | | |/ | +-----+-| NPN + | |> | |+ + - Reverse .-. | ^ protect | | + + 10k | | V Protection diode | '-' - | +----+----+------------------------+ | | | + Anode Equal You may not need the reverse protect diode, but to simulate a real zener as a stand alone in a circuit where reverse flow may occur, this is needed. Your zener voltage would be what you want - ~ 1.8 volts. (2 diode drops and saturation voltage of the NPN) The other protect diode in the emitter must be there for fast turn offs that will generate negative voltage in cases where it will zener the Base-Emitter, you don't want that to happen. With this circuit, you can use very small zeners. Select the proper transistor to handle the power. Jamie
On 4/20/2012 7:00 PM, Jamie wrote:
> panfilero wrote: > >> On Apr 20, 5:46 pm, Bill Martin <w...@wwmartin.net> wrote: >> >>> On 04/20/2012 03:44 PM, panfilero wrote: >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>>> On Apr 20, 3:36 pm, panfilero<panfil...@gmail.com> wrote: >>>> >>>>> I need a 30V zener to drop the a high voltage of 100V down to 60V so I >>>>> can use it with a switch mode power supply chip. So while this >>>>> circuit is in use the zener will be exposed to current pulses from the >>>>> switching, these current pulses are in the neighborhood of 1A. I've >>>>> gone to digikey and pulled up some zeners but I don't see this rating, >>>>> where can I find the rating that tells me whether or not it's ok to >>>>> pulse 1A through my zener? >>> >>>>> here's the one I'm looking at >>> >>>>> http://www.nxp.com/documents/data_sheet/NZX_SER.pdf >>> >>>>> much thanks! >>> >>>> I'm guessing it's in the power rating, if it's a 30V zener, and has a >>>> power rating of 500mW, then max current is I = .5/30 = 17mA.... weak! >>>> but this doesn't tell me about current pulses...spikes... >>> >>> I dunno, but if you are dropping 100V to 60V with a 30V zener, that >>> leaves about 10V of "smoke" to dispose of...:-) >>> >>> bill >> >> >> good point.... let's say for this thread 100 = 90 > why not simply use a transistor to boost the handling of the > zener circuit? > > > > > > Cathode equal > > > + > | > | > +---+-----+------------------------+ > | | | > + | | > z | | > zener diode A | | > + + | > | |/ | > +-----+-| NPN + > | |> | > |+ + - Reverse > .-. | ^ protect > | | + + > 10k | | V Protection diode | > '-' - | > +----+----+------------------------+ > | > | > | > + > > Anode Equal > > > You may not need the reverse protect diode, but to simulate a real zener > as a stand alone in a circuit where reverse flow may occur, this > is needed. > Your zener voltage would be what you want - ~ 1.8 volts. (2 diode drops > and saturation voltage of the NPN) > > The other protect diode in the emitter must be there for fast > turn offs that will generate negative voltage in cases where it will > zener the Base-Emitter, you don't want that to happen. > > With this circuit, you can use very small zeners. Select the proper > transistor to handle the power. > > > Jamie >
Sometimes a solution to the original problem is better than an emulating a component of a bad design. There's something comforting about a pre-regulator circuit that doesn't explode instantly when you short the output to ground.
On Apr 20, 4:36=A0pm, panfilero <panfil...@gmail.com> wrote:
> I need a 30V zener to drop the a high voltage of 100V down to 60V so I > can use it with a switch mode power supply chip. =A0So while this > circuit is in use the zener will be exposed to current pulses from the > switching, these current pulses are in the neighborhood of 1A. =A0I've > gone to digikey and pulled up some zeners but I don't see this rating, > where can I find the rating that tells me whether or not it's ok to > pulse 1A through my zener? > > here's the one I'm looking at > > http://www.nxp.com/documents/data_sheet/NZX_SER.pdf > > much thanks!
30V at 1 amp is 30 watts! That's a big heat sink and maybe a fan too boot. George H.
mike wrote:

> On 4/20/2012 7:00 PM, Jamie wrote: > >> panfilero wrote: >> >>> On Apr 20, 5:46 pm, Bill Martin <w...@wwmartin.net> wrote: >>> >>>> On 04/20/2012 03:44 PM, panfilero wrote: >>>> >>>> >>>> >>>> >>>> >>>> >>>> >>>> >>>> >>>> >>>>> On Apr 20, 3:36 pm, panfilero<panfil...@gmail.com> wrote: >>>>> >>>>>> I need a 30V zener to drop the a high voltage of 100V down to 60V >>>>>> so I >>>>>> can use it with a switch mode power supply chip. So while this >>>>>> circuit is in use the zener will be exposed to current pulses from >>>>>> the >>>>>> switching, these current pulses are in the neighborhood of 1A. I've >>>>>> gone to digikey and pulled up some zeners but I don't see this >>>>>> rating, >>>>>> where can I find the rating that tells me whether or not it's ok to >>>>>> pulse 1A through my zener? >>>> >>>> >>>>>> here's the one I'm looking at >>>> >>>> >>>>>> http://www.nxp.com/documents/data_sheet/NZX_SER.pdf >>>> >>>> >>>>>> much thanks! >>>> >>>> >>>>> I'm guessing it's in the power rating, if it's a 30V zener, and has a >>>>> power rating of 500mW, then max current is I = .5/30 = 17mA.... weak! >>>>> but this doesn't tell me about current pulses...spikes... >>>> >>>> >>>> I dunno, but if you are dropping 100V to 60V with a 30V zener, that >>>> leaves about 10V of "smoke" to dispose of...:-) >>>> >>>> bill >>> >>> >>> >>> good point.... let's say for this thread 100 = 90 >> >> why not simply use a transistor to boost the handling of the >> zener circuit? >> >> >> >> >> >> Cathode equal >> >> >> + >> | >> | >> +---+-----+------------------------+ >> | | | >> + | | >> z | | >> zener diode A | | >> + + | >> | |/ | >> +-----+-| NPN + >> | |> | >> |+ + - Reverse >> .-. | ^ protect >> | | + + >> 10k | | V Protection diode | >> '-' - | >> +----+----+------------------------+ >> | >> | >> | >> + >> >> Anode Equal >> >> >> You may not need the reverse protect diode, but to simulate a real zener >> as a stand alone in a circuit where reverse flow may occur, this >> is needed. >> Your zener voltage would be what you want - ~ 1.8 volts. (2 diode drops >> and saturation voltage of the NPN) >> >> The other protect diode in the emitter must be there for fast >> turn offs that will generate negative voltage in cases where it will >> zener the Base-Emitter, you don't want that to happen. >> >> With this circuit, you can use very small zeners. Select the proper >> transistor to handle the power. >> >> >> Jamie >> > > Sometimes a solution to the original problem is better than an emulating > a component of a bad design. > > There's something comforting about a pre-regulator circuit that doesn't > explode instantly when you short the output to ground.
really, why don't you actually try it instead of assuming it. If it really matters to you, I use that circuit in many, many! clamping protecting circuits for HI-Pot test equipment and HV protection clamps and regulators to increase the handling current on zeners. It works as advertised. Never had one of those fail unless there was some incoming that exceeded the NPN transistor. If that being the case then there is something else wrong and shouldn't be doing that. Also, that circuit is very common from old school. I am not the first one to use that and it's been used in countless designs. So go tell them they are wrong, too! If it would make you feel any better, you could put a R in series with the zener, but really, all that is going to do is slow it down a bit. Jamie
Probably a few microseconds.  Hot spots and junction heating are the 
limiting concerns.  Regular zeners I don't think are going to be rated for 
peaks, but TVS rated diodes do.

As for preregulators, I recall Jeorg telling a story of a similar 
application where a 2N2222 was mysteriously going PFFT, BANG, while being 
well within limits according to most instruments.  A higher bandwidth scope 
indicated ~nanosecond pulses which were invisible on lesser instrumentation 
and, with amplitudes of ~1A peak, where more than sufficient to cause 
troubles.

As Mike said, a current-limited solution is an excellent idea.  Even a good 
BJT circuit may not respond to nanosecond pulses, but a ferrite bead and 
hearty ceramic cap will take care of that kind of stress.

That said, filtering is always the best idea.  Good bypass never hurts, and 
good filtering turns a spikey challenge into a mere bumpy ride.

Tim

-- 
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

"panfilero" <panfilero@gmail.com> wrote in message 
news:9f37100c-30a1-43f9-8ed5-e25288c6900d@c4g2000yqj.googlegroups.com...
>I need a 30V zener to drop the a high voltage of 100V down to 60V so I > can use it with a switch mode power supply chip. So while this > circuit is in use the zener will be exposed to current pulses from the > switching, these current pulses are in the neighborhood of 1A. I've > gone to digikey and pulled up some zeners but I don't see this rating, > where can I find the rating that tells me whether or not it's ok to > pulse 1A through my zener? > > here's the one I'm looking at > > http://www.nxp.com/documents/data_sheet/NZX_SER.pdf > > > much thanks!