Zeners in series...

N

Nox

Guest
Hey there, could somebody take a quick look at this circuit and try to
explain me what's the purpose of the 2 zeners near the interrogative point ?
Here's the schematic: http://img706.imageshack.us/img706/5493/psud.png
If they are working as voltage stabilizer, shouldn't there be a resistor
between them and the rectifier??
To be honest those 2 zeners is what I've found on the circuit but.... the
parts list say that D615 and D614 should be a 120V zener and a 31V 100pF
varactor diode (1S3150A)... this makes no sense to me :S
 
On Mar 12, 2:30 am, "Nox" <a...@def.ghi...ecc...ecc...ecc...> wrote:
Hey there, could somebody take a quick look at this circuit and try to
explain me what's the purpose of the 2 zeners near the interrogative point ?
Here's the schematic:http://img706.imageshack.us/img706/5493/psud.png
If they are working as voltage stabilizer, shouldn't there be a resistor
between them and the rectifier??
To be honest those 2 zeners is what I've found on the circuit but.... the
parts list say that D615 and D614 should be a 120V zener and a 31V 100pF
varactor diode (1S3150A)... this makes no sense to me :S
Click to expand...
Maybe they found two zeners that would split the voltage fine, which
would be cheaper, and forgot to update the parts list.
 
Sansui Samari <jimjam1942@gmail.com> writes:

On Mar 12, 2:30 am, "Nox" <a...@def.ghi...ecc...ecc...ecc...> wrote:
Hey there, could somebody take a quick look at this circuit and try to
explain me what's the purpose of the 2 zeners near the interrogative point ?
Here's the schematic:http://img706.imageshack.us/img706/5493/psud.png
If they are working as voltage stabilizer, shouldn't there be a resistor
between them and the rectifier??
To be honest those 2 zeners is what I've found on the circuit but.... the
parts list say that D615 and D614 should be a 120V zener and a 31V 100pF
varactor diode (1S3150A)... this makes no sense to me :S

Maybe they found two zeners that would split the voltage fine, which
would be cheaper, and forgot to update the parts list.
Click to expand...
A varactor diode there makes even less sense. They probably needed a 270 V
zener as protection against excessive voltage at that location and there
was no single zener that was 270 and adequate power. C603 and the other
component upstream of it limit the current.

--
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Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.
 
In article <rJomn.134582$813.30472@tornado.fastwebnet.it>,
abc@def.ghi...ecc...ecc...ecc... says...
Hey there, could somebody take a quick look at this circuit and try to
explain me what's the purpose of the 2 zeners near the interrogative point ?
Here's the schematic: http://img706.imageshack.us/img706/5493/psud.png
If they are working as voltage stabilizer, shouldn't there be a resistor
between them and the rectifier??
To be honest those 2 zeners is what I've found on the circuit but.... the
parts list say that D615 and D614 should be a 120V zener and a 31V 100pF
varactor diode (1S3150A)... this makes no sense to me :S
Click to expand...
Looks like a 270V clamp to me.
 
In article <rJomn.134582$813.30472@tornado.fastwebnet.it>,
Nox <abc@def.ghi...ecc...ecc...ecc...> wrote:

Hey there, could somebody take a quick look at this circuit and try to
explain me what's the purpose of the 2 zeners near the interrogative point ?

Here's the schematic: http://img706.imageshack.us/img706/5493/psud.png
If they are working as voltage stabilizer, shouldn't there be a resistor
between them and the rectifier??
Click to expand...
It appears to me as if they are, as you say, working as a voltage
stabilizer / regulator.

There is a resistor present, to limit the current flowing through them
and through the rectifier. If you trace out the inputs to the
rectifier bridge, you'll see that one side goes back through
connection 15 and then to the "0V" side of the lowest secondary
winding. The connection to the other input goes to the heavy
horizontal bus (which appears to serve as a ground reference), and
this bus is connected to the "850V" end of the high-voltage secondary
winding through R47 (which is a 3.3M resistor).

So, the winding develops a high AC voltage, which is fed to the bridge
in a current-limited fashion (via R47), rectified to create
high-voltage DC, and the DC voltage is clipped/limited by the
series-connected zeners.

To be honest those 2 zeners is what I've found on the circuit but.... the
parts list say that D615 and D614 should be a 120V zener and a 31V 100pF
varactor diode (1S3150A)... this makes no sense to me :S
Click to expand...
A 31-volt varactor? DOesn't make much sense to me either.

--
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!
 
On Mar 12, 5:30 am, s...@repairfaq.org (Samuel M. Goldwasser) wrote:
Sansui Samari <jimjam1...@gmail.com> writes:
On Mar 12, 2:30 am, "Nox" <a...@def.ghi...ecc...ecc...ecc...> wrote:
Hey there, could somebody take a quick look at this circuit and try to
explain me what's the purpose of the 2 zeners near the interrogative point ?

Maybe they found two zeners that would split the voltage fine,...

A varactor diode there makes even less sense.  They probably needed a 270 V
zener as protection against excessive voltage at that location and there
was no single zener that was 270 and adequate power.  C603 and the other
component upstream of it limit the current.
Click to expand...
If the little blobs at crossing points are to be trusted, C603 isn't
in series there,
and it doesn't limit the current. Winding resistance and rectifier
series
resistance are all I see on this winding leg.

It appears that the whole rectifier/zener assembly is there to limit
AC excursions
of that leg of the transformer winding (the OTHER leg of the
transformer
winding has the high impedance).
 
On Mar 12, 1:15 pm, whit3rd <whit...@gmail.com> wrote:
On Mar 12, 5:30 am, s...@repairfaq.org (Samuel M. Goldwasser) wrote:

Sansui Samari <jimjam1...@gmail.com> writes:
On Mar 12, 2:30 am, "Nox" <a...@def.ghi...ecc...ecc...ecc...> wrote:
Hey there, could somebody take a quick look at this circuit and try to
explain me what's the purpose of the 2 zeners near the interrogative point ?
Maybe they found two zeners that would split the voltage fine,...
A varactor diode there makes even less sense.  They probably needed a 270 V
zener as protection against excessive voltage at that location and there
was no single zener that was 270 and adequate power.  C603 and the other
component upstream of it limit the current.

If the little blobs at crossing points are to be trusted, C603 isn't
in series there,
and it doesn't limit the current.   Winding resistance and rectifier
series
resistance are all I see on this winding leg.

It appears that the whole rectifier/zener assembly is there to limit
AC excursions
of that leg of the transformer winding (the OTHER leg of the
transformer
winding has the high impedance).
Click to expand...
The two zeners in series are there to protect TR607 and C604 in case
the HV regulator circuit fails (or line voltage is excessive) and
TR607 goes into cutoff where HV DC would appear across its C-E
terminals. They clamp the DC to 270V. Two diodes were probably used
since a single 270V device is harder to find or to split up the power
dissipation. Under normal operation, they do not carry any current.
TR607 is probably a 300-400V device.

The high voltage for the CRT cathode (-1kV) is sensed through R631 and
fed to error amplifier TR608. TR608 then controls TR607 inside the DC
loop of bridge rectifier MR3. This allows the transistor to control
(and regulate) the AC voltage delivered to rectifier strings D616-D618
and D621-623. The +3kV is then cross-regulated since it derived from
the same AC voltage as the -1kV. This allows brightness and focus to
be stable under varying AC line voltage.
-Scott
 
<swohlfarth@gmail.com> ha scritto nel messaggio
news:0b1f6556-cc35-43cd-832a-ab0555732ffc@z11g2000yqz.googlegroups.com...
The high voltage for the CRT cathode (-1kV) is sensed through R631 and
fed to error amplifier TR608. TR608 then controls TR607 inside the DC
loop of bridge rectifier MR3. This allows the transistor to control
(and regulate) the AC voltage delivered to rectifier strings D616-D618
and D621-623. The +3kV is then cross-regulated since it derived from
the same AC voltage as the -1kV. This allows brightness and focus to
be stable under varying AC line voltage.
Click to expand...
Thanks everyone for the kind explanations! :D
 
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