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| Author |
Diode identification?
|
|
| John E. 2007-03-02, 1:25 pm |
| It's shorted, burned on the side against the board, the side of the diode
that has part of the p/n printed (of course)...
Best I can make out is (reading around the diode:
ITT
4?
47
Physically it resembles a typical 1A black epoxy rectifier.
Would this be 1n4147? The "47" is clearly visible, and I think I can make out
a "4" in the first part of the poorly-legible digits. No telling how many
digits between the two "4"s.
Any possibilities other than 4147?
Thanks,
--
John English
| |
| Palindrome 2007-03-02, 1:25 pm |
| John E. wrote:
> It's shorted, burned on the side against the board, the side of the diode
> that has part of the p/n printed (of course)...
>
> Best I can make out is (reading around the diode:
> ITT
> 4?
> 47
>
> Physically it resembles a typical 1A black epoxy rectifier.
>
> Would this be 1n4147? The "47" is clearly visible, and I think I can make out
> a "4" in the first part of the poorly-legible digits. No telling how many
> digits between the two "4"s.
>
> Any possibilities other than 4147?
>
Not wishing to trach granny, but this would be my approach:
Reverse engineer parts of the associated circuitry until I am reasonably
confident of what sort of application it is being used for, eg lf
rectifier, hs switch, flywheel, etc. Or more importantly, if it is a
zener.. It is normally not to difficult to work out what the diode is
doing and what sort of currents, voltages and frequencies are happening
to it.
At that point, wire in an external diode with a much, much higher spec
than the original - and measure the actual running parameters. I keep a
few huge and very expensive semiconductors just for this.
Then match a diode to that requirement, by measuring what is actually
happening - with any luck the spec will match to something with a lot of
4s and the odd 7 in its product name.
Assumptions about what things may be tend to bite..
--
Sue
| |
| Genome 2007-03-02, 1:25 pm |
|
"John E." <incognito@yahoo.com> wrote in message
news:0001HW.C20D962501E3C308F01826C8@news.sf.sbcglobal.net...
> It's shorted, burned on the side against the board, the side of the diode
> that has part of the p/n printed (of course)...
>
> Best I can make out is (reading around the diode:
> ITT
> 4?
> 47
>
> Physically it resembles a typical 1A black epoxy rectifier.
>
> Would this be 1n4147? The "47" is clearly visible, and I think I can make
> out
> a "4" in the first part of the poorly-legible digits. No telling how many
> digits between the two "4"s.
>
> Any possibilities other than 4147?
>
> Thanks,
> --
> John English
>
Unfortunately a 1N4147 is a small signal glass diode.......
I would take a guess that what you have got is a zener diode.
Try googling for a 1N4747.
If it's fucked then something else might have fucked it so check the rest of
the circuit. However it sounds like it might have been slowly fucked so you
might want to re-design the circuit.
DNA
| |
| John E. 2007-03-02, 1:25 pm |
| Ah, another ITT diode on the board starts with "ZY" (where "Z" could be
mistaken for a "4" on the charred carcass). So I looked up ZY47 and get a
4.7v power zener diode, 2W.
http://www.allcomponents.ru/diotec/zy47.htm
Also, according to a National data sheet I found, a 1N4147 (a.k.a. 1N914A) is
glass, and way too lightweight physically compared to my charred sample.
Wrong turn, I think.
So it looks like ZY47?
--
John English
| |
| Ben Miller 2007-03-02, 5:25 pm |
| "John E." <incognito@yahoo.com> wrote in message
news:0001HW.C20DB42101EACA0FF01826C8@news.sf.sbcglobal.net...
> Ah, another ITT diode on the board starts with "ZY" (where "Z" could be
> mistaken for a "4" on the charred carcass). So I looked up ZY47 and get a
> 4.7v power zener diode, 2W.
>
> http://www.allcomponents.ru/diotec/zy47.htm
>
> Also, according to a National data sheet I found, a 1N4147 (a.k.a. 1N914A)
> is
> glass, and way too lightweight physically compared to my charred sample.
> Wrong turn, I think.
>
> So it looks like ZY47?
> --
> John English
>
John
You can't just guess at this. As sue suggested, you need to look at the
circuitry and figure out what that diode function is. What is the circuit
for? What components are near the diode? Can you trace the diode connections
to the next devices? What are they? Once that is determined, there are
likely substitute devices that will work just fine, even if you can't
identify the original. I do this all the time as I restore a lot of old test
equipment. It can be a challenge when you don't have the schematic, but
generally you can get there with enough patience and logical thinking.
Ben Miller
--
Benjamin D. Miller, PE
B. MILLER ENGINEERING
www.bmillerengineering.com
| |
| John E. 2007-03-02, 5:25 pm |
| Ben Miller sez:
> You can't just guess at this. As sue suggested, you need to look at the
> circuitry and figure out what that diode function is. ...
OK, here goes:
German-made paper-handling machine, c. 1989. Circuit activates solenoid,
taking several inputs from other sensors, signals, etc.
Anode of unknown diode is to ground, cathode to drain of BUZ72 MOSFET. 1uF
cap also from drain to ground. Drain connects to solenoid. Drive voltage is
42vdc.
Thanks,
--
John English
| |
| Arfa Daily 2007-03-02, 5:25 pm |
|
"John E." <incognito@yahoo.com> wrote in message
news:0001HW.C20DD98F01F38FF6F01826C8@news.sf.sbcglobal.net...
> Ben Miller sez:
>
>
> OK, here goes:
> German-made paper-handling machine, c. 1989. Circuit activates solenoid,
> taking several inputs from other sensors, signals, etc.
>
> Anode of unknown diode is to ground, cathode to drain of BUZ72 MOSFET. 1uF
> cap also from drain to ground. Drain connects to solenoid. Drive voltage
> is
> 42vdc.
>
> Thanks,
> --
> John English
>
Not then, I would suggest, a 4.7v zener ... Sounds like it's just a
flywheeling diode and a 1N4007 would do the job just fine. Does the FET
source go to ground ? Many power MOSFETS have a diode internally in that
orientation across from the source to the drain. It gets there as an
integral side effect of the manufacturing process.
Arfa
| |
| Dave Platt 2007-03-02, 5:25 pm |
| >flywheeling diode and a 1N4007 would do the job just fine. Does the FET
>source go to ground ? Many power MOSFETS have a diode internally in that
>orientation across from the source to the drain. It gets there as an
>integral side effect of the manufacturing process.
Newer designs seem to use a fast-recovery diode (e.g. FRED or HEXFRED
or HiperFRED) for MOSFET flyback protection. 1N4007s aren't
particularly fast, and reverse-conduction losses can be significant if
the switching frequency is high (in e.g. an SMPS). That's probably not
all that much of an issue in a solenoid driver, though.
--
Dave Platt <dplatt@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
| |
| Lostgallifreyan 2007-03-02, 8:25 pm |
| Palindrome <me9@privacy.net> wrote in
news:LQYFh.91285$k82.61028@fe07.news.easynews.com:
> Not wishing to trach granny, but this would be my approach:
>
I hope it doesn't come to that, if she has any breathing difficulties at
all, I imaging it's just due to the rarified air of this place.
| |
| Ben Miller 2007-03-02, 8:25 pm |
| > Anode of unknown diode is to ground, cathode to drain of BUZ72 MOSFET. 1uF
> cap also from drain to ground. Drain connects to solenoid. Drive voltage
> is
> 42vdc.
The diode is a snubber to bypass the inductive kick from the solenoid when
it deenergizes. A 1N4007 will work fine.
Ben Miller
--
Benjamin D. Miller, PE
B. MILLER ENGINEERING
www.bmillerengineering.com
"John E." <incognito@yahoo.com> wrote in message
news:0001HW.C20DD98F01F38FF6F01826C8@news.sf.sbcglobal.net...
| |
| Eeyore 2007-03-02, 8:25 pm |
|
"John E." wrote:
> It's shorted, burned on the side against the board, the side of the diode
> that has part of the p/n printed (of course)...
>
> Best I can make out is (reading around the diode:
> ITT
> 4?
> 47
>
> Physically it resembles a typical 1A black epoxy rectifier.
That's not what either a 1N4147 or 1N4447 looks like.
Graham
| |
| Eeyore 2007-03-02, 8:25 pm |
|
"John E." wrote:
> Ah, another ITT diode on the board starts with "ZY" (where "Z" could be
> mistaken for a "4" on the charred carcass). So I looked up ZY47 and get a
> 4.7v power zener diode, 2W.
>
> http://www.allcomponents.ru/diotec/zy47.htm
>
> Also, according to a National data sheet I found, a 1N4147 (a.k.a. 1N914A) is
> glass, and way too lightweight physically compared to my charred sample.
> Wrong turn, I think.
>
> So it looks like ZY47?
BZY47-C47?
2 watt zener 47V ? The number after the C is the voltage. 4.7 volts would be
BZY47-C4V7 btw.
Graham
| |
| Franc Zabkar 2007-03-02, 8:25 pm |
| On Fri, 02 Mar 2007 16:49:16 GMT, John E. <incognito@yahoo.com> put
finger to keyboard and composed:
>It's shorted, burned on the side against the board, the side of the diode
>that has part of the p/n printed (of course)...
>
>Best I can make out is (reading around the diode:
> ITT
> 4?
> 47
>
>Physically it resembles a typical 1A black epoxy rectifier.
>
>Would this be 1n4147? The "47" is clearly visible, and I think I can make out
>a "4" in the first part of the poorly-legible digits. No telling how many
>digits between the two "4"s.
>
>Any possibilities other than 4147?
>
>Thanks,
Go here ...
http://nte01.nteinc.com/nte/NTExRefSemiProd.nsf/$$Search?OpenForm
.... and type the following into the search box:
1n4*47
- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
| |
| Arfa Daily 2007-03-02, 8:25 pm |
|
"Dave Platt" <dplatt@radagast.org> wrote in message
news:12uh85jomtt65b0@corp.supernews.com...
>
> Newer designs seem to use a fast-recovery diode (e.g. FRED or HEXFRED
> or HiperFRED) for MOSFET flyback protection. 1N4007s aren't
> particularly fast, and reverse-conduction losses can be significant if
> the switching frequency is high (in e.g. an SMPS). That's probably not
> all that much of an issue in a solenoid driver, though.
That was my thought, and the reason that I suggested a KISS approach with a
1N4007
Arfa
| |
| John E. 2007-03-03, 1:25 pm |
| Arfa Daily sez:
> Not then, I would suggest, a 4.7v zener ... Sounds like it's just a
> flywheeling diode and a 1N4007 would do the job just fine. Does the FET
> source go to ground ?
The source connects to a flame-resistant (blue), less-than 1-ohm, 1/4w(?)
resistor (red-violet-gold-gold) that measures about 0.5 ohm. (It should
measure 0.27, yes? Maybe candidate for replacement? But maybe it's my Fluke
77's accuracy at that low setting. Resistor doesn't look abused...) The other
end of the resistor does connect to ground.
> Many power MOSFETS have a diode internally in that
> orientation across from the source to the drain. It gets there as an
> integral side effect of the manufacturing process.
Yes, I've read about the need to short out back-EMF when dealing with relay
coils, solenoids, etc.
So, 1N4007 it is.
An after thought... since the diode was cooked (it actually charred the PCB
beneath it) but the resistor and the FET are OK, maybe the diode needs to be
boosted to a higher A rating? Thoughts?
Thanks to all,
--
John English
| |
|
|
Black ? What size ? I guess 1n4007
1KV , ?1amp , 40 amp surge
____________________________________
On Mar 2, 9:49 am, John E. <incogn...@yahoo.com> wrote:
> It's shorted, burned on the side against the board, the side of the diode
> that has part of the p/n printed (of course)...
>
> Best I can make out is (reading around the diode:
> ITT
> 4?
> 47
>
> Physically it resembles a typical 1A black epoxy rectifier.
>
> Would this be 1n4147? The "47" is clearly visible, and I think I can make out
> a "4" in the first part of the poorly-legible digits. No telling how many
> digits between the two "4"s.
>
> Any possibilities other than 4147?
>
> Thanks,
> --
> John English
| |
| Eeyore 2007-03-03, 1:25 pm |
|
"John E." wrote:
> Arfa Daily sez:
>
>
> The source connects to a flame-resistant (blue), less-than 1-ohm, 1/4w(?)
> resistor (red-violet-gold-gold) that measures about 0.5 ohm. (It should
> measure 0.27, yes? Maybe candidate for replacement? But maybe it's my Fluke
> 77's accuracy at that low setting. Resistor doesn't look abused...) The other
> end of the resistor does connect to ground.
>
>
> Yes, I've read about the need to short out back-EMF when dealing with relay
> coils, solenoids, etc.
>
> So, 1N4007 it is.
>
> An after thought... since the diode was cooked (it actually charred the PCB
> beneath it) but the resistor and the FET are OK, maybe the diode needs to be
> boosted to a higher A rating? Thoughts?
It seems my post aboutt his didn't reach the group.
It's most likely a BZY47-C47 2 watt zener 47V
Graham
| |
| Eeyore 2007-03-03, 1:25 pm |
|
Werty wrote:
> Black ? What size ? I guess 1n4007
You would be wrong.
| |
|
| Late at night, by candle light, Eeyore
<rabbitsfriendsandrelations@hotmail.com> penned this immortal opus:
>
>
>"John E." wrote:
>
>
>BZY47-C47?
>
>2 watt zener 47V ? The number after the C is the voltage. 4.7 volts would be
>BZY47-C4V7 btw.
>
>Graham
Spot-on I think. It'll normally have 42 V across it, not enough to
conduct. When de-energizing there'll be a spike wich it clamps at 47
V. Dunno why the 1 uF cap.
- YD.
--
Remove HAT if replying by mail.
| |
| Eeyore 2007-03-03, 1:25 pm |
|
YD wrote:
> Dunno why the 1 uF cap.
German overkill engineering !
Graham
| |
| Palindrome 2007-03-03, 1:25 pm |
| YD wrote:
> Late at night, by candle light, Eeyore
> <rabbitsfriendsandrelations@hotmail.com> penned this immortal opus:
>
>
>
>
> Spot-on I think. It'll normally have 42 V across it, not enough to
> conduct. When de-energizing there'll be a spike wich it clamps at 47
> V. Dunno why the 1 uF cap.
>
> - YD.
>
So, if all the conduction it should get is from the odd spike, how come
it got the San Quentin hairdo? It takes rather more than static to fry
chips.
My thoughts would be that the supply rails are screwed. If the unit has
a positive and negative rail, it may be that the ground return to the
psu has problems and thus more than the 42v is appearing across the
zener, as the ground point has shifted towards the negative rail.
--
Sue
| |
| Phil Hobbs 2007-03-03, 1:25 pm |
| Dave Platt wrote:
>
> Newer designs seem to use a fast-recovery diode (e.g. FRED or HEXFRED
> or HiperFRED) for MOSFET flyback protection. 1N4007s aren't
> particularly fast, and reverse-conduction losses can be significant if
> the switching frequency is high (in e.g. an SMPS). That's probably not
> all that much of an issue in a solenoid driver, though.
>
1N4007s can take a long time to turn _on_ as well as off. You can get
several volts of overshoot in some applications. Definitely not your
ideal catch diode.
Cheers,
Phil Hobbs
| |
| Arfa Daily 2007-03-03, 8:25 pm |
|
"Phil Hobbs" <pcdh@SpamMeSenseless.pergamos.net> wrote in message
news:45E9C5D0.9080909@SpamMeSenseless.pergamos.net...
> Dave Platt wrote:
>
> 1N4007s can take a long time to turn _on_ as well as off. You can get
> several volts of overshoot in some applications. Definitely not your
> ideal catch diode.
>
> Cheers,
>
> Phil Hobbs
But one that is used by manufacturers world wide for exactly that purpose
....
Arfa
| |
| Terry Given 2007-03-04, 3:25 am |
| Arfa Daily wrote:
> "Phil Hobbs" <pcdh@SpamMeSenseless.pergamos.net> wrote in message
> news:45E9C5D0.9080909@SpamMeSenseless.pergamos.net...
>
>
>
> But one that is used by manufacturers world wide for exactly that purpose
> ...
>
> Arfa
so? just because it gets used doesnt mean its suited for the task. think
bell curve....
BTW in that position its probably a 47V zener, clamping the peak drain
voltage.
Cheers
Terry
| |
| John E. 2007-03-04, 9:25 am |
| Terry Given sez:
> BTW in that position its probably a 47V zener, clamping the peak drain
> voltage.
I'd been turning over in my mind that this is indeed a zener, not simply a
"plain" rectifier. It is indeed a 47 volt zener.
Why was this diode chosen in the design? I'm familiar with the standard diode
being used to short-circuit the back-EMF from the solenoid, but I can't
figure out the purpose of a zener used in this location.
Vdd
/\
|
|
SS
SS Solenoid
SS
|
+-----+
| |
| |
BUZ72 | /---/ ZY47
FET |--+ /\ Diode
-------| |
|--+ |
| |
\ |
0.27R / |
\ |
| |
| |
/// ///
I think that should show proper in Courier or Monaco... or Paris (c:
I must add that Vdd is *reported* to be 42vdc. I was handed this board with
scribbled specs. May be higher or lower or in a parallel universe.
Thanks,
--
John English
| |
| John E. 2007-03-04, 9:25 am |
| ZY47 diode, from the data sheet:
Vz(min) = 44
Vz(max) = 50
I test = 10A
Dynamic R @1khz = 24 (typ)
Vrev = 24
--
John English
| |
| Terry Given 2007-03-04, 9:25 am |
| John E. wrote:
> Terry Given sez:
>
>
>
>
> I'd been turning over in my mind that this is indeed a zener, not simply a
> "plain" rectifier. It is indeed a 47 volt zener.
>
> Why was this diode chosen in the design? I'm familiar with the standard diode
> being used to short-circuit the back-EMF from the solenoid, but I can't
> figure out the purpose of a zener used in this location.
>
> Vdd
> /\
> |
> |
> SS
> SS Solenoid
> SS
> |
> +-----+
> | |
> | |
> BUZ72 | /---/ ZY47
> FET |--+ /\ Diode
> -------| |
> |--+ |
> | |
> \ |
> 0.27R / |
> \ |
> | |
> | |
> /// ///
>
> I think that should show proper in Courier or Monaco... or Paris (c:
>
> I must add that Vdd is *reported* to be 42vdc. I was handed this board with
> scribbled specs. May be higher or lower or in a parallel universe.
>
> Thanks,
If Vdd was 42V, then a 47V zener sticks 5V reverse voltage across the
coil, so the current will decay 5/42 times faster than it built up.
Whereas if you just use a conventional freewheeling diode, Anode to
Drain, Cathode to Vdd, there is 0.7V(ish) reverse voltage across the
coil when the FET turns off, so the coil current decays 5/0.7V times
slower than the 47V zener.
Of course the actual zener voltage wont be 47V, it'll be higher,
depending on the actual current.
One can achieve the same objective at lower loss with a 4.3V zener in
zeries with a freewheeling diode, but thats 2 parts.
So it is possible that the zener was used to get a suitable rate of
decay (although ramp down is more accurate) of coil current.
Or perhaps the designer was a bit stupid, used no freewheeling diode,
then discovered the FET broke, so added the zener. You might be
surprised how many shit designs make it to market.
Cheers
Terry
| |
| Palindrome 2007-03-04, 9:25 am |
| John E. wrote:
> Terry Given sez:
>
>
>
>
> I'd been turning over in my mind that this is indeed a zener, not simply a
> "plain" rectifier. It is indeed a 47 volt zener.
>
> Why was this diode chosen in the design? I'm familiar with the standard diode
> being used to short-circuit the back-EMF from the solenoid, but I can't
> figure out the purpose of a zener used in this location.
The zener does a better, but more expensive, job of protecting the
series switching element. It limits both positive and negative
transients. A diode across the switched inductor does stop most (but not
all) of the switching transient - but doesn't protect the series element
from transients on the supply rails, caused by other inductances
elsewhere reacting to the sudden change in current. It is usual to
combine these sorts of design with reasonably fast (eg
tantalum)electrolytics placed locally - to act as energy "tanks" to
supply and sink transient power.
>
> Vdd
> /\
> |
> |
> SS
> SS Solenoid
> SS
> |
> +-----+
> | |
> | |
> BUZ72 | /---/ ZY47
> FET |--+ /\ Diode
> -------| |
> |--+ |
> | |
> \ |
> 0.27R / |
> \ |
> | |
> | |
> /// ///
>
> I think that should show proper in Courier or Monaco... or Paris (c:
>
> I must add that Vdd is *reported* to be 42vdc. I was handed this board with
> scribbled specs. May be higher or lower or in a parallel universe.
>
As I and others have written - the diode didn't burn up because of
transient energy. There is a supply problem, somewhere.
--
Sue
| |
| Terry Given 2007-03-04, 9:25 am |
| Palindrome wrote:
> John E. wrote:
>
>
>
> The zener does a better, but more expensive, job of protecting the
> series switching element. It limits both positive and negative
> transients.
its pretty hard finding a FET without a body diode, so negative
transients are invariably taken care of regardless of the type of clamp
circuit.
A diode across the switched inductor does stop most (but not
> all) of the switching transient - but doesn't protect the series element
> from transients on the supply rails,
by "series element" you must be referring to the FET. Yep, the zener
will protect the FET against voltage spikes on the 42V bus. Of course
FETs nowadays are rated for avalanche energy.....
caused by other inductances
> elsewhere reacting to the sudden change in current.
Que?
It is usual to
> combine these sorts of design with reasonably fast (eg
> tantalum)electrolytics placed locally - to act as energy "tanks" to
> supply and sink transient power.
seeing as Im being a pedantic sod, I'll point out that tantalums are not
electrolytics (and vice versa).
I once had a serious brain fart in this regard, making a small motor
controller at Uni. It ran from a 3-phase supply, and seeing as
full-wave-rectified 3-phase AC has ~15% ripple, I figured I didnt need a
DC bus cap.
Which worked fine, until the first time I turned the H-bridge off with
current flowing in the motor  30 minutes, 4 FETs and a complete set of
gate drive circuits later, I added a large cap. oops.
>
>
> As I and others have written - the diode didn't burn up because of
> transient energy. There is a supply problem, somewhere.
>
assuming the thing ever worked properly, which it sounds like it did.
conceivably a shorted solenoid could have stored enough energy to end up
snotting the zener, but as you say, a supply overvoltage would
definitely kill it. And it doesnt even have to be that much, just
continuous.
Cheers
Terry
| |
| Palindrome 2007-03-04, 9:25 am |
| Terry Given wrote:
> Palindrome wrote:
>
>
>
> its pretty hard finding a FET without a body diode, so negative
> transients are invariably taken care of regardless of the type of clamp
> circuit.
Hence why I wrote "series switching element" rather than FET. If the
designer was brought up designing using pnp/npn transistors, he may have
always protected them this way.
>
> A diode across the switched inductor does stop most (but not
>
>
>
> by "series element" you must be referring to the FET. Yep, the zener
> will protect the FET against voltage spikes on the 42V bus. Of course
> FETs nowadays are rated for avalanche energy.....
>
>
> caused by other inductances
>
>
>
> Que?
The power distribution and supply system connected to the load will,
itself have a transient response (eg have series inductance) and may
easily overshoot following step changes in load.
>
> It is usual to
>
>
>
> seeing as Im being a pedantic sod, I'll point out that tantalums are not
> electrolytics (and vice versa).
"Tantalums
Tantalum capacitors are also electrolytic, constructed with a very
porous anode made with tantalum powder. This powder is pressed into a
pellet form with a tantalum wire inserted."
http://www.electronicproducts.com/p...tw.may2006.html
>
> I once had a serious brain fart in this regard, making a small motor
> controller at Uni. It ran from a 3-phase supply, and seeing as
> full-wave-rectified 3-phase AC has ~15% ripple, I figured I didnt need a
> DC bus cap.
>
> Which worked fine, until the first time I turned the H-bridge off with
> current flowing in the motor 30 minutes, 4 FETs and a complete set of
> gate drive circuits later, I added a large cap. oops.
>
>
>
> assuming the thing ever worked properly, which it sounds like it did.
>
> conceivably a shorted solenoid could have stored enough energy to end up
> snotting the zener, but as you say, a supply overvoltage would
> definitely kill it. And it doesnt even have to be that much, just
> continuous.
I'd go for the continuous - every time where component and circuit board
burning were evident.
--
Sue
| |
| Terry Given 2007-03-04, 9:25 am |
| Palindrome wrote:
> Terry Given wrote:
>
>
>
> Hence why I wrote "series switching element" rather than FET. If the
> designer was brought up designing using pnp/npn transistors, he may have
> always protected them this way.
its surprising how much stuff ends up being designed that way -
"because", rather than having a good reason.
>
>
>
> The power distribution and supply system connected to the load will,
> itself have a transient response (eg have series inductance) and may
> easily overshoot following step changes in load.
>
now thats a nicely worded sentence.
>
> "Tantalums
> Tantalum capacitors are also electrolytic, constructed with a very
> porous anode made with tantalum powder. This powder is pressed into a
> pellet form with a tantalum wire inserted."
> http://www.electronicproducts.com/p...tw.may2006.html
>
ya got me
common usage of "electrolytic" refers to ye olde carboxylic acid-style
electrolytes, for whatever reason tantalums are always called tantalums.
>
>
> I'd go for the continuous - every time where component and circuit board
> burning were evident.
it all depends on how much transient energy there was. when working with
big stuff, components can (and do) disappear completely. If any form of
arc develops as a result of some transient phenomenon, its pretty easy
to burn big holes in things.
and a transient that snots the zener will make it fail short-circuit
(unless it disappears), at which point it will then fry.
however such pontification is essentially meaningless; the supply rail
needs to be checked....
Cheers
Terry
| |
| John E. 2007-03-04, 1:25 pm |
| Palindrome sez:
> Hence why I wrote "series switching element" rather than FET. If the
> designer was brought up designing using pnp/npn transistors, he may have
> always protected them this way.
Interesting you mention this... the silkscreen for the FET says "b-e-c".
Seems that the original design was for BJT, but component specs were changed
to include FET sometime in production with little regard for the confusion it
would cause service personnel who saw these markings...
Does this shed any different light on the choice of zener for this purpose?
And the possibility for a different replacement part? The 47v, 2W part is
looking like unobtanium...
Thanks,
--
John English
| |
| John E. 2007-03-04, 1:25 pm |
| Palindrome sez:
> As I and others have written - the diode didn't burn up because of
> transient energy. There is a supply problem, somewhere.
The pcb had failed 'lytic caps (ends pushed out), so that could have added to
the problem. Or, being beyond a certain age, the 'lytic problem may lie in
the PS as well. I'll see about 'scoping the PS voltages in the machine.
--
John English
| |
| John E. 2007-03-04, 1:25 pm |
| Palindrome sez:
> I'd go for the continuous - every time where component and circuit board
> burning were evident.
The reason this machine drew attention in the first place was because the
solenoid valve was gummed up and sticking. I wouldn't think that this would
cause problems with the drive circuit. Au contraire, it would result in no
back-emf.
--
John English
| |
| John E. 2007-03-04, 1:25 pm |
| Terry Given sez:
> So it is possible that the zener was used to get a suitable rate of
> decay (although ramp down is more accurate) of coil current.
I'm told that the solenoid this circuit operates is for a vacuum valve that
must operate quickly and repeatedly. It was thought by the person who handed
me this pcb that the solenoid was operated with 2 voltage rails, switching
between opposite opening voltage and closing voltage. But according to
measurements by him (and the fact that there's only 1 FET), the purpose of
the zener here seems to make sense.
But how can a 4.7v zener and one diode drop serve similar purpose as a 47v
part?
--
John English
| |
| John Popelish 2007-03-04, 1:25 pm |
| John E. wrote:
> Palindrome sez:
>
>
> The reason this machine drew attention in the first place was because the
> solenoid valve was gummed up and sticking. I wouldn't think that this would
> cause problems with the drive circuit. Au contraire, it would result in no
> back-emf.
I would think that a partially shorted zener would keep the
solenoid energized, giving a "gummed up" symptom. If the
board allows space for the modification, I would replace the
47 volt zener with a series combination of a 4.7 or 5.1 volt
zener in series with a 1N400X or similar small rectifier
diode, connected directly across the coil, instead of across
the fet. Such a low voltage zener will be a lot more rugged
(dissipating only a small fraction of the power dumped
into the 47 volt zener, since it discharges only the
solenoid energy, rather than that energy plus lots more from
the supply). The energy dump per solenoid discharge is so
much lower you may get by with a .75 or .5 watt zener and a
1N4148 diode, if the solenoid current is less than about .1
amp.
The rectifier cathode connects toward the positive supply
end of the solenoid, but the zener cathode points toward the
fet drain.
Can you find a place to put those two components?
| |
| John Popelish 2007-03-04, 1:25 pm |
| John E. wrote:
> Terry Given sez:
>
>
> I'm told that the solenoid this circuit operates is for a vacuum valve that
> must operate quickly and repeatedly. It was thought by the person who handed
> me this pcb that the solenoid was operated with 2 voltage rails, switching
> between opposite opening voltage and closing voltage. But according to
> measurements by him (and the fact that there's only 1 FET), the purpose of
> the zener here seems to make sense.
>
> But how can a 4.7v zener and one diode drop serve similar purpose as a 47v
> part?
In the present circuit, when the fet turns off, the coil
generates a voltage in the direction that tries to keep the
current going. That means that the end that had been pulled
negative to ground suddenly goes more positive than the 42
volt rail. At 47 volts the zener comes on, and provides a
path for the decaying coil current. So, during that energy
dump process, there is about 47-42=5 volts reverse voltage
across the coil, driving the current toward zero. But the
energy in the zener is being fed from both the coil (the 5
volt part of the 470 and by the supply the 42 volt part of
the 47), since the coil current is also passing through the
supply.
The only advantage I can see to this wasteful and stressful
(to the zener) method of driving the coil current to zero,
is that the supply current ramps down to zero, smoothly,
rather than switching off as the fet does. But I doubt that
is a consideration in this circuit.
If you put a rectifier and zener directly across the coil,
the rectifier keeps the zener out of the circuit when the
fet is on, but connects it as a voltage clamp when the fet
switches off. Now, the only energy going into the zener is
that being dumped out of the solenoid, as its current ramps
down to zero. The supply stops contributing the moment the
fet switches off. You can adjust the ramp down time by
swapping zeners with different break down voltages. But I
would start with a 4.7 or 5.1 volt unit to get things back
about the way they were to start. But a 6.8 or 7.5 volt
unit may make the solenoid work better with an insignificant
additional voltage stress for the fet.
The supply should also have some bypass capacitance
connected very close to the fet source and the positive
supply connection of the solenoid, to make sure the fast
interruption of the current (that didn't happen with the old
zener) doesn't bounce the supply rails around enough to
unset either the fet gate drive or some other load connect
to the 42 volt or ground rails. A microfarad or 10 would do
it. I 1 microfarad, 50 or 63 volt stacked film type would
do it well.
see:
http://www.panasonic.com/industrial.../abd0000ce8.pdf
| |
|
|
| Eeyore 2007-03-04, 1:25 pm |
|
"John E." wrote:
> Terry Given sez:
>
>
> I'm told that the solenoid this circuit operates is for a vacuum valve that
> must operate quickly and repeatedly. It was thought by the person who handed
> me this pcb that the solenoid was operated with 2 voltage rails, switching
> between opposite opening voltage and closing voltage. But according to
> measurements by him (and the fact that there's only 1 FET), the purpose of
> the zener here seems to make sense.
>
> But how can a 4.7v zener and one diode drop serve similar purpose as a 47v
> part?
Consider how it works !
Graham
| |
| Eeyore 2007-03-04, 1:25 pm |
|
John Popelish wrote:
> John E. wrote:
>
> I would think that a partially shorted zener would keep the
> solenoid energized, giving a "gummed up" symptom. If the
> board allows space for the modification, I would replace the
> 47 volt zener with a series combination of a 4.7 or 5.1 volt
> zener in series with a 1N400X or similar small rectifier
> diode, connected directly across the coil, instead of across
> the fet. Such a low voltage zener will be a lot more rugged
> (dissipating only a small fraction of the power dumped
> into the 47 volt zener, since it discharges only the
> solenoid energy, rather than that energy plus lots more from
> the supply). The energy dump per solenoid discharge is so
> much lower you may get by with a .75 or .5 watt zener and a
> 1N4148 diode, if the solenoid current is less than about .1
> amp.
>
> The rectifier cathode connects toward the positive supply
> end of the solenoid, but the zener cathode points toward the
> fet drain.
>
> Can you find a place to put those two components?
The usual trick is to stand them 'on end' with their common connection 'up in the
air'.
Graham
| |
| John E. 2007-03-04, 1:25 pm |
| Eeyore sez:
> Is it against your religion to substitute ?
Not at all. Here in USA I checked my 3 regular sources: Mouser, DigiKey, and
Jameco with nil results, subs or not.
But it looks like design changes are afoot (see other recent posts in this
thread).
Thanks,
--
John English
| |
| John E. 2007-03-04, 5:25 pm |
| John Popelish sez:
> I would think that a partially shorted zener would keep the
> solenoid energized, giving a "gummed up" symptom. If the
> board allows space for the modification, I would replace the
> 47 volt zener with a series combination of a 4.7 or 5.1 volt
> zener in series with a 1N400X or similar small rectifier
> diode, connected directly across the coil, instead of across
> the fet.
What I know of the design goal of this circuit is that it must activate the
solenoid quickly from off to on and quickly from on to off with as little
"ramping" as possible. With the given circuit, what does this knowledge say
about the selection of possible replacement component(s)?
> The rectifier cathode connects toward the positive supply
> end of the solenoid, but the zener cathode points toward the
> fet drain.
Anode-to-anode, with the rectifier "on top", the pair being connected across
the solenoid?
> Can you find a place to put those two components?
Yes, pretty easily. It's not too heavily populated. Lots of "vertical
implementation" possible (c:
Thanks for your suggestions, John.
--
John English
| |
| Terry Given 2007-03-04, 5:25 pm |
| John E. wrote:
> John Popelish sez:
>
>
>
>
> What I know of the design goal of this circuit is that it must activate the
> solenoid quickly from off to on and quickly from on to off with as little
> "ramping" as possible. With the given circuit, what does this knowledge say
> about the selection of possible replacement component(s)?
>
V = L*dI/dt, so dt = L*dI/V
L & dI are constant, you are increasing V to get a nice low dt.
the BUZ72 is a 100V part, so you have PLENTY of headroom there.
the existing circuit turns the solenoid off about 8x slower than it
turns it on.
>
>
>
> Anode-to-anode, with the rectifier "on top", the pair being connected across
> the solenoid?
it doesnt matter if the rectifier is on the "top" or "bottom", only that
its cathode faces towards the supply, so it prevents the zener from
working when the FET is on, and allows the zener to work when the FET
drain voltage rises above the supply.
so a K-K connection with the recitifer at the bottom and the zener at
the top, or A-A with the zener at the bottom and the rectifier at the top.
>
>
>
>
> Yes, pretty easily. It's not too heavily populated. Lots of "vertical
> implementation" possible (c:
>
> Thanks for your suggestions, John.
Cheers
Terry
| |
| Eeyore 2007-03-04, 5:25 pm |
|
"John E." wrote:
> Eeyore sez:
>
>
> Not at all. Here in USA I checked my 3 regular sources: Mouser, DigiKey, and
> Jameco with nil results, subs or not.
You mean that in the entire USA there is no such thing as 47V 2-3W zener diode ?
Graham
| |
| John Popelish 2007-03-04, 5:25 pm |
| John E. wrote:
> What I know of the design goal of this circuit is that it must activate the
> solenoid quickly from off to on and quickly from on to off with as little
> "ramping" as possible. With the given circuit, what does this knowledge say
> about the selection of possible replacement component(s)?
Well, there is nothing these diodes can do about the turn on
time. That is a function of the supply voltage and the coil
inductance. You would have to raise the supply voltage and
add enough series resistance to limit the steady state
current to a safe value to speed up turn on.
>
> Anode-to-anode, with the rectifier "on top", the pair being connected across
> the solenoid?
Order doesn't matter, only orientation.
Higher zener voltage means faster current ramp down. But
you will probably have to go quite a bit higher to see much
difference. The resistive drop of the coil is already
starting the ramp down with a 42 volt reverse voltage. But
that drop falls as the current falls, so the zener is really
there to speed the tail of the process, unless its initial
voltage is on the order of the supply voltage. So you might
consider one as high as 22 to 39 volts. But then I would
look for a 1 watt unit, to handle the power pulse that will
end up more there than in the coil resistance. But you
should definitely see some decrease in the power down time,
to about 37% if what you will get from a 4.7 volt zener if
you switch to a 33 volt one. So you can see that the turn
off time is not dominated by the zener till its voltage gets
near the supply voltage. But increasing the zener voltage
drop helps.
| |
| John E. 2007-03-04, 5:25 pm |
| >> Not at all. Here in USA I checked my 3 regular sources: Mouser, DigiKey, and
Keyword here is "regular".
[color=darkred]
> You mean that in the entire USA there is no such thing as 47V 2-3W zener
> diode ?
>
> Graham
Nyet.
But point is moot, it seems. See recent posts to thread re. design change.
--
John English
| |
| John E. 2007-03-04, 5:25 pm |
| John Popelish sez:
> Higher zener voltage means faster current ramp down. But
> you will probably have to go quite a bit higher to see much
> difference. The resistive drop of the coil is already
> starting the ramp down with a 42 volt reverse voltage. But
> that drop falls as the current falls, so the zener is really
> there to speed the tail of the process, unless its initial
> voltage is on the order of the supply voltage. So you might
> consider one as high as 22 to 39 volts. But then I would
> look for a 1 watt unit, to handle the power pulse that will
> end up more there than in the coil resistance. But you
> should definitely see some decrease in the power down time,
> to about 37% if what you will get from a 4.7 volt zener if
> you switch to a 33 volt one. So you can see that the turn
> off time is not dominated by the zener till its voltage gets
> near the supply voltage. But increasing the zener voltage
> drop helps.
Seems we're creeping back up toward the original 47v zener (although it was
connected across the FET, not the coil). Any advantage to simply using
another 47v part along with the rect. in the configuration you recommend? Is
this a case of "bigger (v) is better"?
Thanks again,
--
John English
| |
| John Popelish 2007-03-04, 5:25 pm |
| John E. wrote:
> John Popelish sez:
>
>
> Seems we're creeping back up toward the original 47v zener (although it was
> connected across the FET, not the coil). Any advantage to simply using
> another 47v part along with the rect. in the configuration you recommend? Is
> this a case of "bigger (v) is better"?
The advantage in moving the zener is the lower energy
absorbed per discharge (for the reason I explained earlier).
At 47 inverse volts across the coil, you are getting pretty
close to the 100 volt mark, which will stress the fet a bit
more. Are you confident in its ability to handle that
voltage? And there is a point of diminishing returns. The
37% discharge time I gave above referred to the time for the
current to reach zero. But that is not really the time for
the magnetic field to reach zero, because the iron parts of
the solenoid will circulate eddy currents that support the
field for a bit. Then there is the inertial time constant
of the mechanism that delay s movement, after the magnetic
field stops holding it against the return spring.
If you used a 1000 volt zener, the coil current would hit
zero in a really short amount of time, but the valve would
close in just about the same time as if you used a 500 volt
zener.
My gut feeling is that, unless this solenoid and valve
mechanism were designed with fastest possible reaction time
in mind, going much above 22 volts on the zener will not pay
off in much decreased valve action.
But a handful of 1 watt zeners in the range of 4.7 volts to
47 volts cost only a few bucks, if you want to take the
experimental route. Can you rig up some mechanical pickup
on the valve, so you can, measure the response time effect
of various zeners? That would make it pretty obvious where
the diminishing returns come into play.
A better way to speed the release might be to put a parallel
resistor and capacitor in series with the coil, so that the
coil voltage actually decreases a little after the cap
charges to the IR drop of steady state operation. That way,
you have the large pick up force to get the valve open, but
a reduced holding force to keep it open, so there is less
magnetic field to quench when you want it to close. This is
called a pick and hold strategy, and there are special
driver chips that perform this function with two switches,
one on each side of the coil.
At energize, both switches turn on, applying full voltage
(often a voltage the coil would not tolerate, continuously)
to the coil to ramp the magnetic field up as fast as
possible. The current is sensed, and when the required pick
current is reached, one of the switches pulse width
modulates the current down to the hold value. When turn off
time arrives, both switches open, and the coil dumps its
energy back into the supply through a diode across each of
the switches. So the supply voltage acts like your zener
voltage. Very fast and energy efficient (there is minimal
heat in the coil, and no intentional power wasted anywhere
else in the circuit) but probably not practical as a
retrofit in this case.
http://www.ortodoxism.ro/datasheets...ronics/1331.pdf
But something to keep in mind if a board layout comes along.
| |
|
| On 2007-03-04, Terry Given <my_name@ieee.org> wrote:
> John E. wrote:
[color=darkred]
[color=darkred]
>
> If Vdd was 42V, then a 47V zener sticks 5V reverse voltage across the
> coil, so the current will decay 5/42 times faster than it built up.
42V turning on 5v turning off, I get 5/42 fraction as fast. (about 1/8 the
speed)
> Whereas if you just use a conventional freewheeling diode, Anode to
> Drain, Cathode to Vdd, there is 0.7V(ish) reverse voltage across the
> coil when the FET turns off, so the coil current decays 5/0.7V times
> slower than the 47V zener.
huh I'm getting 42/0.7 (which is over 50 times slower)
are you assuming a 5V vcc? OP claims 42V.
> Or perhaps the designer was a bit stupid, used no freewheeling diode,
> then discovered the FET broke, so added the zener. You might be
> surprised how many shit designs make it to market.
>
> Cheers
> Terry
--
Bye.
Jasen
| |
| Terry Given 2007-03-10, 3:25 am |
| jasen wrote:
> On 2007-03-04, Terry Given <my_name@ieee.org> wrote:
>
>
>
>
>
>
>
>
>
> 42V turning on 5v turning off, I get 5/42 fraction as fast. (about 1/8 the
> speed)
read harder.
5/42 = 0.118. 0.118 times faster is, indeed, slower. admittedly I didnt
have to make it a reading comprehension test, but its more amusing this way.
>
>
>
>
> huh I'm getting 42/0.7 (which is over 50 times slower)
>
> are you assuming a 5V vcc? OP claims 42V.
no, the original voltage across the coil during turn-off is Vz - Vcc =
47 - 42 = 5V. When a freewheeling diode is used, the voltage across the
coil is 0.7V.
so the current ramps down 5V/0.7V ~ 7x slower with a freewheeling diode.
note the not-so-confusing sentence. I should have written:
"so the current ramps down 0.7V/5V times faster with a freewheeling diode"
but I'm being nice ;)
[color=darkred]
>
>
Cheers
Terry
| |
| Tony Williams 2007-03-10, 3:25 am |
| In article <1173503476.441339@ftpsrv1>,
Terry Given <my_name@ieee.org> wrote:
> jasen wrote:
[color=darkred]
> no, the original voltage across the coil during turn-off is Vz -
> Vcc = 47 - 42 = 5V. When a freewheeling diode is used, the
> voltage across the coil is 0.7V.
You blokes have forgotten R and L, and L/R. :-)
I couldn't be bothered to do the sums so just LTspice'd
a quick 42V supply, 100mH and 42 ohm coil, switched by
a MOSFET and clamped by a Schottky diode to a variable
voltage.
The current Risetime at switchon, from 0.1A to 1A was
about 5.5mS, as per the L/R exponential sum.
Below is a little table of LTspice current Falltimes.
Vclamp. Falltime (1A to 0.1A).
42 5.3mS <-- nearly equal to the L/R Risetime.
47 3.9 <-- only 1.3x 5.3mS.
57 2.6
84 1.4 <-- Changing from an L/R sum to
mainly a V = L.dI/dT sum.
--
Tony XXXXXXXX.
| |
| Terry Given 2007-03-10, 9:25 am |
| Terry Given wrote:
> jasen wrote:
>
>
>
> read harder.
>
> 5/42 = 0.118. 0.118 times faster is, indeed, slower. admittedly I didnt
> have to make it a reading comprehension test, but its more amusing this
> way.
>
>
>
> no, the original voltage across the coil during turn-off is Vz - Vcc =
> 47 - 42 = 5V. When a freewheeling diode is used, the voltage across the
> coil is 0.7V.
>
> so the current ramps down 5V/0.7V ~ 7x slower with a freewheeling diode.
>
> note the not-so-confusing sentence. I should have written:
>
> "so the current ramps down 0.7V/5V times faster with a freewheeling diode"
>
> but I'm being nice ;)
>
>
> Cheers
> Terry
Tony XXXXXXXX just pointed out my mistake.
I'm so used to dealing with SMPS inductors I forgot we were talking
about a solenoid.
In a SMPS inductor (or transformer) some external circuit is used to
limit the current - pulse width, peak current control etc, and in order
to minimise losses, Rdc is very small. In which case V = LdI/dt is the
"right" equation to use (as I*R is very small)
but a solenoid or relay isnt (generally) used that way - Rdc sets the
current, and is most assuredly not "very small", and of course I*R = Vcc
which is not "very small"
in which case its more about L/R time constants. I = Vcc/R, so when you
switch the solenoid off, the voltage across the internal inductance
rises to Vcc (because of I*R) + Vclamp.
So the difference between 42+5 and 42+0.7 is bugger all, and the
difference in decay time is, likewise, bugger all - well not bugger all,
but certainly not 7x.
Oops.
Cheers
Terry
|
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