Forums

2N3904 maximum ratings Vceo Vcbo

Started by Bill Bowden May 2, 2015
Is it safe to operate a 2N3904 in a switching application with a supply 
voltage of 48 volts? The data sheet says Vceo is 40  and Vcbo is 60 volts. 
When the transistor switches off, the collector to emitter voltage will be 
48 and the base voltage will be near 0 through a resistor. Any problems with 
that?




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On Sat, 02 May 2015 19:45:51 -0700, Bill Bowden wrote:

> Is it safe to operate a 2N3904 in a switching application with a supply > voltage of 48 volts? The data sheet says Vceo is 40 and Vcbo is 60 > volts. When the transistor switches off, the collector to emitter > voltage will be 48 and the base voltage will be near 0 through a > resistor. Any problems with that?
Why not just use a snubber diode across the inductor and be sure?
On Sat, 2 May 2015 19:45:51 -0700, "Bill Bowden"
<bperryb@bowdenshobbycircuits.info> wrote:

>Is it safe to operate a 2N3904 in a switching application with a supply >voltage of 48 volts? The data sheet says Vceo is 40 and Vcbo is 60 volts. >When the transistor switches off, the collector to emitter voltage will be >48 and the base voltage will be near 0 through a resistor. Any problems with >that? >
As long as the base is not floating (the Vceo case) you'll be OK. The base-grounded case is sometimes denoted Vcer (b-e resistor) or Vcex (shorted), and is about equal to Vcbo. Keep the base resistor low, like 1K or something. -- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Sun, 03 May 2015 10:55:18 -0700, John Larkin
<jlarkin@highlandtechnology.com> wrote:

>On Sat, 2 May 2015 19:45:51 -0700, "Bill Bowden" ><bperryb@bowdenshobbycircuits.info> wrote: > >>Is it safe to operate a 2N3904 in a switching application with a supply >>voltage of 48 volts? The data sheet says Vceo is 40 and Vcbo is 60 volts. >>When the transistor switches off, the collector to emitter voltage will be >>48 and the base voltage will be near 0 through a resistor. Any problems with >>that? >> > >As long as the base is not floating (the Vceo case) you'll be OK. > >The base-grounded case is sometimes denoted Vcer (b-e resistor) or >Vcex (shorted), and is about equal to Vcbo. > >Keep the base resistor low, like 1K or something.
BVcbo = Collector-to-base breakdown, emitter open BVceo = Collector-to-emitter breakdown, base open BVcer = Collector-to-emitter breakdown, base-to-emitter resistor BVces = Collector-to-emitter breakdown, base-to-emitter shorted BVcex = Collector-to-emitter breakdown, base-to-emitter reverse biased etc See.. <https://www.onsemi.com/pub/Collateral/AN1628-D.PDF> ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On Sat, 2 May 2015 19:45:51 -0700, "Bill Bowden"
<bperryb@bowdenshobbycircuits.info> Gave us:

>Is it safe to operate a 2N3904 in a switching application with a supply >voltage of 48 volts? The data sheet says Vceo is 40 and Vcbo is 60 volts. >When the transistor switches off, the collector to emitter voltage will be >48 and the base voltage will be near 0 through a resistor. Any problems with >that? >
Absolutely presents a problem... This will let the smoke out. No question.
On Thu, 07 May 2015 16:36:08 -0400, DecadentLinuxUserNumeroUno
<DLU1@DecadentLinuxUser.org> wrote:

>On Sat, 2 May 2015 19:45:51 -0700, "Bill Bowden" ><bperryb@bowdenshobbycircuits.info> Gave us: > >>Is it safe to operate a 2N3904 in a switching application with a supply >>voltage of 48 volts? The data sheet says Vceo is 40 and Vcbo is 60 volts. >>When the transistor switches off, the collector to emitter voltage will be >>48 and the base voltage will be near 0 through a resistor. Any problems with >>that? >> > > Absolutely presents a problem... > > This will let the smoke out. No question.
That's only 8 volts above the Vceo spec. No problem. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Thu, 07 May 2015 13:51:28 -0700, John Larkin
<jlarkin@highlandtechnology.com> wrote:

>On Thu, 07 May 2015 16:36:08 -0400, DecadentLinuxUserNumeroUno ><DLU1@DecadentLinuxUser.org> wrote: > >>On Sat, 2 May 2015 19:45:51 -0700, "Bill Bowden" >><bperryb@bowdenshobbycircuits.info> Gave us: >> >>>Is it safe to operate a 2N3904 in a switching application with a supply >>>voltage of 48 volts? The data sheet says Vceo is 40 and Vcbo is 60 volts. >>>When the transistor switches off, the collector to emitter voltage will be >>>48 and the base voltage will be near 0 through a resistor. Any problems with >>>that? >>> >> >> Absolutely presents a problem... >> >> This will let the smoke out. No question. > >That's only 8 volts above the Vceo spec. No problem.
Depends on the load-line... a snubber of some sort might be necessary. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On Thu, 07 May 2015 13:51:28 -0700, John Larkin
<jlarkin@highlandtechnology.com> Gave us:

>On Thu, 07 May 2015 16:36:08 -0400, DecadentLinuxUserNumeroUno ><DLU1@DecadentLinuxUser.org> wrote: > >>On Sat, 2 May 2015 19:45:51 -0700, "Bill Bowden" >><bperryb@bowdenshobbycircuits.info> Gave us: >> >>>Is it safe to operate a 2N3904 in a switching application with a supply >>>voltage of 48 volts? The data sheet says Vceo is 40 and Vcbo is 60 volts. >>>When the transistor switches off, the collector to emitter voltage will be >>>48 and the base voltage will be near 0 through a resistor. Any problems with >>>that? >>> >> >> Absolutely presents a problem... >> >> This will let the smoke out. No question. > >That's only 8 volts above the Vceo spec. No problem.
Pretty fucking unprofessional statement, Larkin. I ran two to drive the front end of my HV switcher drives into transformer. One designs within the spec, not over it, dipshit. A 1N4001 can do 1000V, but there is no way I would use them in a multiplier. Folks spec EL and even solid state caps at just over half their rated voltage. You seem to not even know, much less understand why.
On Thu, 07 May 2015 14:06:55 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

>On Thu, 07 May 2015 13:51:28 -0700, John Larkin ><jlarkin@highlandtechnology.com> wrote: > >>On Thu, 07 May 2015 16:36:08 -0400, DecadentLinuxUserNumeroUno >><DLU1@DecadentLinuxUser.org> wrote: >> >>>On Sat, 2 May 2015 19:45:51 -0700, "Bill Bowden" >>><bperryb@bowdenshobbycircuits.info> Gave us: >>> >>>>Is it safe to operate a 2N3904 in a switching application with a supply >>>>voltage of 48 volts? The data sheet says Vceo is 40 and Vcbo is 60 volts. >>>>When the transistor switches off, the collector to emitter voltage will be >>>>48 and the base voltage will be near 0 through a resistor. Any problems with >>>>that? >>>> >>> >>> Absolutely presents a problem... >>> >>> This will let the smoke out. No question. >> >>That's only 8 volts above the Vceo spec. No problem. > >Depends on the load-line... a snubber of some sort might be necessary. > > ...Jim Thompson
Not the classic load line, but if there's an unclamped inductive load, the flyback could be hundreds of volts. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Fri, 08 May 2015 02:54:45 -0400, DecadentLinuxUserNumeroUno
<DLU1@DecadentLinuxUser.org> wrote:

>On Thu, 07 May 2015 13:51:28 -0700, John Larkin ><jlarkin@highlandtechnology.com> Gave us: > >>On Thu, 07 May 2015 16:36:08 -0400, DecadentLinuxUserNumeroUno >><DLU1@DecadentLinuxUser.org> wrote: >> >>>On Sat, 2 May 2015 19:45:51 -0700, "Bill Bowden" >>><bperryb@bowdenshobbycircuits.info> Gave us: >>> >>>>Is it safe to operate a 2N3904 in a switching application with a supply >>>>voltage of 48 volts? The data sheet says Vceo is 40 and Vcbo is 60 volts. >>>>When the transistor switches off, the collector to emitter voltage will be >>>>48 and the base voltage will be near 0 through a resistor. Any problems with >>>>that? >>>> >>> >>> Absolutely presents a problem... >>> >>> This will let the smoke out. No question. >> >>That's only 8 volts above the Vceo spec. No problem. > > > Pretty fucking unprofessional statement, Larkin.
I pointed out to him that he should not leave the base open, which is what Vceo measures. I wouldn't pick a 2N3904 for a 48 volt application, but if he already has them, the risk of using them is nil. Actually, I wouldn't use a 2N3904 for anything. Klunky old beast. We don't have any in stock.
> > I ran two to drive the front end of my HV switcher drives into >transformer. > > One designs within the spec, not over it, dipshit.
One designs things that work and can be sold.
> > A 1N4001 can do 1000V, but there is no way I would use them in a >multiplier.
Too slow, mostly. And thru-hole axial!
> > Folks spec EL and even solid state caps at just over half their rated >voltage. You seem to not even know, much less understand why.
Sometimes I derate caps, and sometimes I use them at over their rated voltages. Low voltage ceramic caps can stand 10x or 20x their rated voltages; you just lose capacitance. Tantalums can run at rated voltage in some cases, or should be derated 3:1 in others. We were just yesterday discussing how much power we can dissipate into standard surface-mount resistors. It's safe to go way over their ratings if you put decent power pours on the end caps. Datasheet specs are sort of arbitrary anyhow. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com