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'[EE]: Norp12'
2002\10\31@165404 by =?iso-8859-1?Q?=C5ke_Neehr?=

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part 1 1798 bytes content-type:multipart/alternative; (decoded quoted-printable)


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2002\10\31@201810 by Roman Black

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face
What is a .PUB file and why are you sending a
weird file to the piclist?? This is not a standard
image file or even a schematic standard. :o(

If you must send files PLEASE make sure it is a
standard image like .GIF or better still send an
ascii text image.
-Roman



Eke Neehr wrote:
{Quote hidden}

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'[EE]: Norp12'
2002\11\01@095246 by =?iso-8859-1?Q?=C5ke_Neehr?=
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part 1 2034 bytes content-type:multipart/alternative; (decoded quoted-printable)


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2002\11\01@100145 by Roman Black

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face
Eke Neehr wrote:
>
> Sorry for the wrong format before
> but here I4m attaching a shema in .GIF
> format on a circuit I have some problem with.
> The relay don4t switch over directly without
> stands and vibrations before it changed.
> What is wrong?

>                               Name: Norp12.gif
>                Part 1.2       Type: GIF Image (image/gif)
>                           Encoding: base64



Thanks for using a standard format now. :o)
Try adding a 1uF capacitor between base and
emitter of the transistor, and maybe another
one across the 2 lower resistors.
-Roman

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2002\11\01@101759 by Rick C.
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Looks like it is transitioning in the linear region. Transistor will get
hot before the relay closes, unless the light transition is steeper.
Maybe a zener in the base circuit will help, or add another transistor
and make a schmidt trigger.
Rick

Roman Black wrote:

{Quote hidden}

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2002\11\01@123611 by Olin Lathrop

face picon face
>>
Sorry for the wrong format before
but here I´m attaching a shema in .GIF
format on a circuit I have some problem with.
The relay don´t switch over directly without
stands and vibrations before it changed.
What is wrong?
<<

The gain is low and there is no hysteresis.  When the light level changes
slowly the relay will be slowly driven thru the on/off range.  One
additional transistor stage would get you lots of gain and an opportunity
to supply a little bit of positive feedback.  This will make the relay
snap on or off, although there will be a small difference in the on->off
light threshold as the off->on light threshold.


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(978) 742-9014, http://www.embedinc.com

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2002\11\02@061331 by Peter L. Peres

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On Fri, 1 Nov 2002, Olin Lathrop wrote:

*>The gain is low and there is no hysteresis.  When the light level changes
*>slowly the relay will be slowly driven thru the on/off range.  One

Imho it is very hard to drive a relay slowly through its on-off range
because most relays have a linear spring and a quadratic magnetic force
component. This causes built-in hysteresis on both make and break.

Otoh in Ake's circuit any ac (including from arcing contacts) can make it
to the base and contribute to a positive feedback loop.

Peter

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2002\11\02@061337 by Peter L. Peres

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1. You are trying it in a lab and you have fluorescent lights on
2. The 12V power supply is weak and drops when the relay pulls in

In both cases adding a 1uF capacitor between base and collector should
help.

Peter

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2002\11\03@123030 by =?iso-8859-1?Q?=C5ke_Neehr?=

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----- Original Message ----- From: "Peter L. Peres" <KILLspamplpKILLspamspamACTCOM.CO.IL>
To: <RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU>
Sent: Saturday, November 02, 2002 10:03 AM
Subject: Re: [EE]: Norp12

Hello!

No, I don´t trying in lab. I´m testing outdoors
and the relay vibrating when it has to turn off
in the twilight and turn on the lamp!
To place a 1 uF cap between collector
and base don´t works at all !

Regards
ÅkeN

{Quote hidden}

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2002\11\04@091142 by Roman Black

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No, the cap goes between the base and EMITTER,
NOT the collector! Putting the cap between base
and collector is stupid as it couples the back emf
to turn the transistor back on, exactly the reason
you are getting vibration now.

I said clearly in my post to put the cap between
B-E, and if you need extra filtering another cap
across the bottom 2 resistors. The relay itself
has significant hysteresis so a single transistor
driver will work ok IF you put the cap in the right
place! :o)
-Roman



Eke Neehr wrote:

{Quote hidden}

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2002\11\04@114123 by Peter L. Peres

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On Sun, 3 Nov 2002, Åke Neehr wrote:

*>----- Original Message -----
*>From: "Peter L. Peres" <TakeThisOuTplpEraseMEspamspam_OUTACTCOM.CO.IL>
*>To: <RemoveMEPICLISTspamTakeThisOuTMITVMA.MIT.EDU>
*>Sent: Saturday, November 02, 2002 10:03 AM
*>Subject: Re: [EE]: Norp12
*>
*>Hello!
*>
*>No, I don´t trying in lab. I´m testing outdoors
*>and the relay vibrating when it has to turn off
*>in the twilight and turn on the lamp!
*>To place a 1 uF cap between collector
*>and base don´t works at all !

Huh ? Why not ? It should work but slower. How is your power supply ? Any
connection with those filter caps you removed to make the lamp work at
the right voltage ?

Peter

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2002\11\04@134056 by Peter L. Peres

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On Tue, 5 Nov 2002, Roman Black wrote:

*>No, the cap goes between the base and EMITTER,
*>NOT the collector! Putting the cap between base
*>and collector is stupid as it couples the back emf
*>to turn the transistor back on, exactly the reason
*>you are getting vibration now.

He isn't getting vibration, he said it does not work at all, it does not
couple back emf anywhere (it's not stupid, it's a Miller integrator which
makes the capacitor appear beta times larger exactly when it matters for
noise (during the transition)(but without the leakage, bulk and price of a
100uF filter cap), and *I* said put it between C and B, not you. Please
check your facts before contra-posting. You can also build the circuit and
see for yourself.

Peter

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2002\11\04@134059 by Peter L. Peres

picon face
On Tue, 5 Nov 2002, Roman Black wrote:

*>Eke Neehr wrote:
*>
*>> No, I don4t trying in lab. I4m testing outdoors
*>> and the relay vibrating when it has to turn off
*>> in the twilight and turn on the lamp!
*>> To place a 1 uF cap between collector
*>> and base don4t works at all !

And just in case it has anything to do with the lamp where you removed the
filter caps you do need a filtered supply for this circuit. For example
by using:

                      D1N4004  Z12V1W  470uF40V
Unfiltered            o-----AK--KA--*---||---GND
                                   |
                                   IN
                            7812      GND---GND
                                   OUT
                                   |
                                   v
                                 your circuit power supply

The zener reduces the voltage to something the 7812 will accept.

Peter

PS: I presume you want to run the lamp on dc because it has some sort of
inverter in it - like it's a lf lamp.

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2002\11\05@081105 by Roman Black

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Peter L. Peres wrote:
>
> On Tue, 5 Nov 2002, Roman Black wrote:
>
> *>No, the cap goes between the base and EMITTER,
> *>NOT the collector! Putting the cap between base
> *>and collector is stupid as it couples the back emf
> *>to turn the transistor back on, exactly the reason
> *>you are getting vibration now.
>
> He isn't getting vibration, he said it does not work at all,


Wrong. I quote: "No, I don4t trying in lab.
I4m testing outdoors and the relay vibrating when
it has to turn off"

> it does not
> couple back emf anywhere

Wrong again, it's an NPN transistor driving a
relay with it's collector, therefore when the
relay turns off the collector goes high (to
about 1v higher to turn on the catch diode) and
WHEN the collector goes high your suggestion of
a cap to the base WILL turn the transistor back
on, giving exactly the vibration he complained of.
You may have forgot that the transistor is driven
from a slowly changing analogue voltage, and when
turning off the base will be JUST below 0.6v.
Any + going voltage at the base will cause the
vibration he complained of.

> (it's not stupid, it's a Miller integrator

I know *you're* not stupid and I respect your
opinion and experience, BUT that suggestion
sure was. ;o)

> Please
> check your facts before contra-posting.

Since you posted a stupid suggestion and then
were wrong TWICE in your rebuttal to me I suggest
you check your facts. :o)

No need to apologise, just put it down to
experience. A cap C-B in that circuit is stupid,
a cap B-E will fix his problem.
-Roman

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2002\11\05@082333 by Michael Rigby-Jones

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> -----Original Message-----
> From: Roman Black [SMTP:fastvidEraseMEspam.....EZY.NET.AU]
> Sent: Tuesday, November 05, 2002 1:05 PM
> To:   EraseMEPICLISTspamMITVMA.MIT.EDU
> Subject:      Re: [EE]: Norp12
>
> Wrong again, it's an NPN transistor driving a
> relay with it's collector, therefore when the
> relay turns off the collector goes high (to
> about 1v higher to turn on the catch diode) and
> WHEN the collector goes high your suggestion of
> a cap to the base WILL turn the transistor back
> on, giving exactly the vibration he complained of.
> You may have forgot that the transistor is driven
> from a slowly changing analogue voltage, and when
> turning off the base will be JUST below 0.6v.
> Any + going voltage at the base will cause the
> vibration he complained of.
>
Surely the transistor will only just conduct enough to keep 0.6 volts on the
base, the transistor will not be able to be entirely switched off until the
cap is charged.  This would effectively cause the relay to switch off very
slowly.  I certainly don't see how this is going to cause an oscillation as
the cap is effectively providing NEGATIVE feedback at anything over DC.

Regards

Mike

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2002\11\05@082749 by Olin Lathrop

face picon face
> A cap C-B in that circuit is stupid,
> a cap B-E will fix his problem.

Maybe.  It depends on where the feedback is coming from that causes the
oscillations.  He said the relay was "vibrating" or something like that
during the transition.  The circuit is just a DC amplifier driving the
relay, and as you said, relays do have some inherent hysterisis.  We also
know his input signal varies very slowly (outdoor ambient light at dusk).

So, why does it oscillate at the threshold input?  One possibility could
be AC noise coupled back into the amplifier from the switching transients.
Your cap from B to E should help with that.

However, I suspect at least part of his problem is DC feedback via the
power supply when voltages change due to the relay switching on
significant power.  A B-E cap won't fix that, only decrease the
oscillation frequency.  I think the best way to address both problems
together is to spend a few more cents and add another transistor stage.
This will give him more gain and provide an easy opportunity for some
deliberate positive feedback in the amplifier to get some hysterisis.
This will always drive the relay solidly on or off, and should provide the
necessary noise immunity.  It will also make insensitive to small
variations in light level at the thresholds, like a cloud momentarily
passing over the sun shortly after it has set.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

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2002\11\05@111440 by Roman Black

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Michael Rigby-Jones wrote:

> > Wrong again, it's an NPN transistor driving a
> > relay with it's collector, therefore when the
> > relay turns off the collector goes high (to
> > about 1v higher to turn on the catch diode) and
> > WHEN the collector goes high your suggestion of
> > a cap to the base WILL turn the transistor back
> > on, giving exactly the vibration he complained of.

> Surely the transistor will only just conduct enough to keep 0.6 volts on the
> base, the transistor will not be able to be entirely switched off until the
> cap is charged.  This would effectively cause the relay to switch off very
> slowly.  I certainly don't see how this is going to cause an oscillation as
> the cap is effectively providing NEGATIVE feedback at anything over DC.


The relay won't switch off slowly as such, what
happens is it drops out when it reaches about
4v, and won't pull in again until about 9v.
All that is required is a cap to slow any change
in the transistor because it is B-E and changes
there must happen slowly.

Peter's suggestion of putting the cap C-B is bad
as when the relay rutns off the collector goes to
PSU+1v, the cap couples this sudden rise directly
back to the base and it makes a good oscillator.
B-E makes it oscillate less, C-B makes it oscillate
more. :o)
-Roman

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2002\11\05@113344 by Alan B. Pearce

face picon face
>The relay won't switch off slowly as such, what
>happens is it drops out when it reaches about
>4v, and won't pull in again until about 9v.
>All that is required is a cap to slow any change
>in the transistor because it is B-E and changes
>there must happen slowly.

Well I have not followed the discussion on this closely, but do not recall
seeing this mentioned.

My first thought on seeing the description of the symptoms is that the power
supply has a lot of impedance in it, and when the relay tries to pull in the
supply voltage drops to a point where there is not enough volts for the
relay to hold in, and so drops out. this will create an oscillatory state,
which IIRC was the original problem. If this is correct, then no capacitor
anywhere but on the power supply (along with some heavier wires) is going to
fix the situation.

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2002\11\05@113346 by Roman Black

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Olin Lathrop wrote:
>
> > A cap C-B in that circuit is stupid,
> > a cap B-E will fix his problem.
>
> Maybe.  It depends on where the feedback is coming from that causes the
> oscillations.  He said the relay was "vibrating" or something like that
> during the transition.  The circuit is just a DC amplifier driving the
> relay, and as you said, relays do have some inherent hysterisis.  We also
> know his input signal varies very slowly (outdoor ambient light at dusk).

Yes he said it was vibrating when the relay
was turning off, and that he had added a cap
C-B which Peter suggested. Which would cause that
problem exactly.


> So, why does it oscillate at the threshold input?  One possibility could
> be AC noise coupled back into the amplifier from the switching transients.
> Your cap from B to E should help with that.

The LDR and resistors are some 10's of kohms
and a 1uF or larger cap B-E would fix that due
to the large RC time constant, it simply can't
oscillate as the hysteresis of the relay is huge.
Only back-emf or as you mentioned supply voltage
rise could cause the oscillation on turnoff.
Both would be fixed by adding a cap B-E.
I also said if further filtering was needed to
add another cap on the lower resistors which is
basically a PI filter.

I've built many one transistor relay driving
circuits like this, they have enough gain for most
uses as the 12v relay pulls in at about 9v and
drops out at 4v or so. The low gain and slowly
changing analogue voltage won't matter.


> However, I suspect at least part of his problem is DC feedback via the
> power supply when voltages change due to the relay switching on
> significant power.  A B-E cap won't fix that, only decrease the
> oscillation frequency.

Yes I assumed that his PSU had a decent size cap
across it. Further decoupling the relay PSU from
the LDR PSU would help.

>  I think the best way to address both problems
> together is to spend a few more cents and add another transistor stage.
> This will give him more gain and provide an easy opportunity for some
> deliberate positive feedback in the amplifier to get some hysterisis.
> This will always drive the relay solidly on or off, and should provide the
> necessary noise immunity.  It will also make insensitive to small
> variations in light level at the thresholds, like a cloud momentarily
> passing over the sun shortly after it has set.

Sure another gain stage would be a step forward
but might not really be necessary. It also might
worsen the situation with clouds etc as the one
stage system will rely on large relay hysteresis
to mean that the relay won't pull in until a
large difference in light levels. I built a 1-tran
light relay once and had problems with too much
sensitivity, one transistor may be ideal for this
provided he has larger enough caps B-E.
-Roman

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2002\11\05@114142 by Roman Black

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Alan B. Pearce wrote:

> My first thought on seeing the description of the symptoms is that the power
> supply has a lot of impedance in it, and when the relay tries to pull in the
> supply voltage drops to a point where there is not enough volts for the
> relay to hold in, and so drops out. this will create an oscillatory state,
> which IIRC was the original problem. If this is correct, then no capacitor
> anywhere but on the power supply (along with some heavier wires) is going to
> fix the situation.


No, because the cap B-E is fed through resistors
of tens of kohms. Coupled with the large hysteresis
of the relay itself all that is required is to
slow changes at the base. The difference between
typical pull-in and drop-out voltages are around
2:1 or 3:1, which is way outside the expected
PSU variations.

He said the vibration problem occured at relay
turn-off, and then adding a cap C-B as Peter
suggested didn't fix it. I'm not surprised.
-Roman

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2002\11\05@162637 by Peter L. Peres

picon face
On Tue, 5 Nov 2002, Michael Rigby-Jones wrote:

*>Surely the transistor will only just conduct enough to keep 0.6 volts on the
*>base, the transistor will not be able to be entirely switched off until the
*>cap is charged.  This would effectively cause the relay to switch off very
*>slowly.  I certainly don't see how this is going to cause an oscillation as
*>the cap is effectively providing NEGATIVE feedback at anything over DC.

Correct but I have to add again that relays do not switch slowly. As I
said before the magnetic force generated by the coil depends on the
inverse square of the gap and relays have a well known 'catch' and
'release' voltage, far apart from each other. Just try to make an ordinary
relay switch 'slowly'. Use a benchtop regulated psu as accurate as you
wish.

The capacitor on CB is equivalent to a capacitor across BE where Cbe ~=
Ccb * beta I think. This is most useful since it causes negative feedback
in ac there where the transistor has most gain (which in this circuit
amplifies noise). The beta is relatively low when the transistor is off or
saturated and there the capacitor plays a smaller role. So entering and
leaving saturation and off state is less slowed down than with a Cbe cap.
Also a 1uF plastic cap will have significantly lower leakage than a 100uF
electrolytic.

Peter

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2002\11\05@170218 by Jim

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 "The beta is relatively low when the transistor is off"

Condition, transistor off (no base drive),

Beta = Ic / Ib ...

With Ic =10 uA (leakage)
and  Ib = 0

Ic / Ib => undefined

RF Jim


{Original Message removed}

2002\11\06@141030 by Peter L. Peres

picon face
On Wed, 6 Nov 2002, Roman Black wrote:

*>Peter's suggestion of putting the cap C-B is bad
*>as when the relay rutns off the collector goes to
*>PSU+1v, the cap couples this sudden rise directly
*>back to the base and it makes a good oscillator.
*>B-E makes it oscillate less, C-B makes it oscillate
*>more. :o)

Please please please build that circuit before posting more like this. For
any oscillations to take place in that circuit the capacitor should have
at least 90 degrees of phase shift in it at the preferred resonant
frequency and the necessary gain would require a superbeta transistor and
a relay with a loaded coil Q in the hundreds. Which is impossible by
definition (the collector current of the transistor is loading it down).

Peter

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2002\11\07@025534 by Michael Rigby-Jones

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{Quote hidden}

Absolutetly, I did word that rather badly.  I meant the voltage accross the
relay would fall rather slowly, obviously once the magnetic field has become
small enough the contacts will open at pretty much the same speed.

> The capacitor on CB is equivalent to a capacitor across BE where Cbe ~=
> Ccb * beta I think. This is most useful since it causes negative feedback
> in ac there where the transistor has most gain (which in this circuit
> amplifies noise). The beta is relatively low when the transistor is off or
> saturated and there the capacitor plays a smaller role. So entering and
> leaving saturation and off state is less slowed down than with a Cbe cap.
> Also a 1uF plastic cap will have significantly lower leakage than a 100uF
> electrolytic.
>
Yep, that's how I see it.  I did simulate the circuit with the cap accross
CB just to make sure and couldn't persuade it to oscillate at all.

Mike

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2002\11\07@031119 by Vasile Surducan

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On Thu, 7 Nov 2002, Michael Rigby-Jones wrote:

> > The beta is relatively low when the transistor is off or
> > saturated and there the capacitor plays a smaller role.

???
Vasile

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2002\11\07@034454 by Michael Rigby-Jones

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> -----Original Message-----
> From: Vasile Surducan [SMTP:vasileSTOPspamspamspam_OUTS3.ITIM-CJ.RO]
> Sent: Thursday, November 07, 2002 8:25 AM
> To:   spamBeGonePICLISTSTOPspamspamEraseMEMITVMA.MIT.EDU
> Subject:      Re: [EE]: Norp12
>
> On Thu, 7 Nov 2002, Michael Rigby-Jones wrote:
>
> > > The beta is relatively low when the transistor is off or
> > > saturated and there the capacitor plays a smaller role.
>
> ???
> Vasile
>
Hmm, that was Peter's quote, not mine.

Mike

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2002\11\07@035514 by Vasile Surducan

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On Thu, 7 Nov 2002, Michael Rigby-Jones wrote:

> > -----Original Message-----
> > From: Vasile Surducan [SMTP:EraseMEvasilespamEraseMES3.ITIM-CJ.RO]
> > Sent: Thursday, November 07, 2002 8:25 AM
> > To:   @spam@PICLIST@spam@spamspam_OUTMITVMA.MIT.EDU
> > Subject:      Re: [EE]: Norp12
> >
> > On Thu, 7 Nov 2002, Michael Rigby-Jones wrote:
> >
> > > > The beta is relatively low when the transistor is off or
> > > > saturated and there the capacitor plays a smaller role.
> >
> > ???
> > Vasile
> >
> Hmm, that was Peter's quote, not mine.
>
 good, then he need to reconsider a little this theory ... :)

 Vasile

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2002\11\07@174120 by Peter L. Peres

picon face
On Thu, 7 Nov 2002, Vasile Surducan wrote:
*>On Thu, 7 Nov 2002, Michael Rigby-Jones wrote:

No, I wrote that

*>> > The beta is relatively low when the transistor is off or
*>> > saturated and there the capacitor plays a smaller role.
*>???

The Ccb capacitor appears as itself (Ccb) when the transistor is off or
firmly saturated (because dUc ~= 0 on both cases). It has the value
beta*(1+Ccb) when the transistor is in the dynamic region (between off and
saturated). The resistor (coil) load will essentially have the entire
supply voltage across it after a certain Ic will  have been reached.

Peter

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