The diode across the E-B junction of Q1 was added, mostly to prevent
zenering and then beta reduction.
D1 is removed for the waveforms seen; it clamps the negative swing
seen at V3 (and the +20V supply current increases with reduced HV output).
The question is, if the voltage on C5 is changed from about +10V to
+50V, that negative swing DOES NOT change, but the positive swing of Vc
does.
Can anyone explain how and why?

On Sun, 15 Aug 2010 00:24:10 -0700, Robert Baer
wrote:

The diode across the E-B junction of Q1 was added, mostly to prevent
zenering and then beta reduction.
D1 is removed for the waveforms seen; it clamps the negative swing
seen at V3 (and the +20V supply current increases with reduced HV output).
The question is, if the voltage on C5 is changed from about +10V to
+50V, that negative swing DOES NOT change, but the positive swing of Vc
does.
Can anyone explain how and why?

Transformer polarity reversed?

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

Spice is like a sports car...
Performance only as good as the person behind the wheel.

On Sun, 15 Aug 2010 00:24:10 -0700, Robert Baer
wrote:

The diode across the E-B junction of Q1 was added, mostly to prevent
zenering and then beta reduction.
D1 is removed for the waveforms seen; it clamps the negative swing
seen at V3 (and the +20V supply current increases with reduced HV output).
The question is, if the voltage on C5 is changed from about +10V to
+50V, that negative swing DOES NOT change, but the positive swing of Vc
does.
Can anyone explain how and why?

This looks like it's operating as a forward converter, and it looks to
me like the transformer is saturating. If that's true, it would work
better if the ON time of Q1 were reduced.

If it's saturating, that would explain why the flyback voltage
(negative spike at TP2) isn't changing as the C5 voltage changes.

John

Yuck!

U1A is awfully slow (~500Hz?), U1D input is being overdriven, Q1 has weak
drive, yet a huge "speedup" capacitor, and U1D's output is pretty much
short circuited into C3-Q1 and C3-(diode). R3 and R4 hardly do anything.
Transformer polarity is not indicated, so we don't even know if you have
it backwards or not, but it hardly matters because D1 shorts it out anyway
(if not for R2-C2 narrowing the pulse width).

Q1's hFE isn't terribly high, and it's got 2N3904-ish current capacity.
It's no MOSFET. That transformer better have at least 2mH primary
inductance. If not, that would be why you observe constant voltage drop,
it's already in the constant current region.

Offhand, you could use a circuit like this:
http://webpages.charter.net/dawill/t..._Generator.gif
The toroid is probably #43. It should really be gapped, in which case a
much smaller toroid (or more likely, E or U core with coil former) will
work, with many more turns of course.

There are other circuits that would do a better job. A proper flyback
supply is easy to make, using a UC3842 in the appnote circuit, or a
(discrete or IC) BCM flyback. Royer oscillator also comes to mind:
simple, low noise, easy to regulate.

In any case, for a watt or two output, figure a thousand turns or so of
rather fine wire (#40). Something resonant or quasi-resonant will help
mitigate the winding capacitance and leakage inductance inevitable in such
a transformer.

Tim

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

"Robert Baer" wrote in message
net...
The diode across the E-B junction of Q1 was added, mostly to prevent
zenering and then beta reduction.
D1 is removed for the waveforms seen; it clamps the negative swing
seen at V3 (and the +20V supply current increases with reduced HV
output).
The question is, if the voltage on C5 is changed from about +10V to
+50V, that negative swing DOES NOT change, but the positive swing of Vc
does.
Can anyone explain how and why?

On Sun, 15 Aug 2010 12:53:42 -0500, "Tim Williams"
wrote:

Yuck!

U1A is awfully slow (~500Hz?), U1D input is being overdriven, Q1 has weak
drive, yet a huge "speedup" capacitor, and U1D's output is pretty much
short circuited into C3-Q1 and C3-(diode). R3 and R4 hardly do anything.
Transformer polarity is not indicated, so we don't even know if you have
it backwards or not, but it hardly matters because D1 shorts it out anyway
(if not for R2-C2 narrowing the pulse width).

Q1's hFE isn't terribly high, and it's got 2N3904-ish current capacity.
It's no MOSFET. That transformer better have at least 2mH primary
inductance. If not, that would be why you observe constant voltage drop,
it's already in the constant current region.

Offhand, you could use a circuit like this:
http://webpages.charter.net/dawill/t..._Generator.gif
The toroid is probably #43. It should really be gapped, in which case a
much smaller toroid (or more likely, E or U core with coil former) will
work, with many more turns of course.

There are other circuits that would do a better job. A proper flyback
supply is easy to make, using a UC3842 in the appnote circuit, or a
(discrete or IC) BCM flyback. Royer oscillator also comes to mind:
simple, low noise, easy to regulate.

In any case, for a watt or two output, figure a thousand turns or so of
rather fine wire (#40). Something resonant or quasi-resonant will help
mitigate the winding capacitance and leakage inductance inevitable in such
a transformer.

Tim


A simple forware converter isn't a bad way to make a low-current HV
supply. It's quasi-regulated all by itself, since the hv Vout is just
the supply voltage times the transformer ratio. It needs to operate at
low duty cycles and short pulse widths, but that's OK for a
low-current HV app.

Note the 2M output resistor!

John

"John Larkin" wrote in
message ...
Note the 2M output resistor!

That's supposed to be 2M? I was a bit confused and just ignored it since
it's labeled as 2*m*...

Tim

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

Jim Thompson wrote:
On Sun, 15 Aug 2010 00:24:10 -0700, Robert Baer
wrote:

The diode across the E-B junction of Q1 was added, mostly to prevent
zenering and then beta reduction.
D1 is removed for the waveforms seen; it clamps the negative swing
seen at V3 (and the +20V supply current increases with reduced HV output).
The question is, if the voltage on C5 is changed from about +10V to
+50V, that negative swing DOES NOT change, but the positive swing of Vc
does.
Can anyone explain how and why?

Transformer polarity reversed?

...Jim Thompson
Do not think so, in any even that does not explain the "soft
clamping" (waveshape does not change) of that peak.

John Larkin wrote:
On Sun, 15 Aug 2010 00:24:10 -0700, Robert Baer
wrote:

The diode across the E-B junction of Q1 was added, mostly to prevent
zenering and then beta reduction.
D1 is removed for the waveforms seen; it clamps the negative swing
seen at V3 (and the +20V supply current increases with reduced HV output).
The question is, if the voltage on C5 is changed from about +10V to
+50V, that negative swing DOES NOT change, but the positive swing of Vc
does.
Can anyone explain how and why?

This looks like it's operating as a forward converter, and it looks to
me like the transformer is saturating. If that's true, it would work
better if the ON time of Q1 were reduced.

If it's saturating, that would explain why the flyback voltage
(negative spike at TP2) isn't changing as the C5 voltage changes.

John



Ahh...will check that out; thanks.

Tim Williams wrote:
Yuck!

U1A is awfully slow (~500Hz?), U1D input is being overdriven, Q1 has weak
drive, yet a huge "speedup" capacitor, and U1D's output is pretty much
short circuited into C3-Q1 and C3-(diode). R3 and R4 hardly do anything.
Transformer polarity is not indicated, so we don't even know if you have
it backwards or not, but it hardly matters because D1 shorts it out anyway
(if not for R2-C2 narrowing the pulse width).

Q1's hFE isn't terribly high, and it's got 2N3904-ish current capacity.
It's no MOSFET. That transformer better have at least 2mH primary
inductance. If not, that would be why you observe constant voltage drop,
it's already in the constant current region.

Offhand, you could use a circuit like this:
http://webpages.charter.net/dawill/t..._Generator.gif
The toroid is probably #43. It should really be gapped, in which case a
much smaller toroid (or more likely, E or U core with coil former) will
work, with many more turns of course.

There are other circuits that would do a better job. A proper flyback
supply is easy to make, using a UC3842 in the appnote circuit, or a
(discrete or IC) BCM flyback. Royer oscillator also comes to mind:
simple, low noise, easy to regulate.

In any case, for a watt or two output, figure a thousand turns or so of
rather fine wire (#40). Something resonant or quasi-resonant will help
mitigate the winding capacitance and leakage inductance inevitable in such
a transformer.

Tim

R4 was added to drain base leakage currents at 200C.
Custom transformers are rather expensive and so are avoided where
possible.
I mentioned that D1 is not connected for the presented case (if put
in place, the negative "spike" is removed/clamped).
Rather than the Triad "Red" SP-4, the Tamura MET-01 can also be
used; not both are audio transformers that were not meant to generate
1-2KV and certainly not in the 185-200C region.

Tim Williams wrote:
"John Larkin" wrote in
message ...
Note the 2M output resistor!

That's supposed to be 2M? I was a bit confused and just ignored it since
it's labeled as 2*m*...

Tim

Sorry, not my schematic and i did not look carefully: 2 milliohms is
absurd in a high voltage application

Robert Baer a écrit :
John Larkin wrote:
On Sun, 15 Aug 2010 00:24:10 -0700, Robert Baer
wrote:

The diode across the E-B junction of Q1 was added, mostly to
prevent zenering and then beta reduction.
D1 is removed for the waveforms seen; it clamps the negative swing
seen at V3 (and the +20V supply current increases with reduced HV
output).
The question is, if the voltage on C5 is changed from about +10V to
+50V, that negative swing DOES NOT change, but the positive swing of
Vc does.
Can anyone explain how and why?

This looks like it's operating as a forward converter, and it looks to
me like the transformer is saturating. If that's true, it would work
better if the ON time of Q1 were reduced.

If it's saturating, that would explain why the flyback voltage
(negative spike at TP2) isn't changing as the C5 voltage changes.

John



Ahh...will check that out; thanks.

It's more like Q1 is desaturating: look how vc gets back up to 20V at
t=200us while Q1 is still driven "hard" Ib = 140uA with a given 40-160
HFE range for the 2N3439... That makes for about 15mA max collector current.

Checking the +20V current will sort that out.


--
Thanks,
Fred.

On Sun, 15 Aug 2010 23:50:59 -0700, Robert Baer
wrote:

Tim Williams wrote:
"John Larkin" wrote in
message ...
Note the 2M output resistor!

That's supposed to be 2M? I was a bit confused and just ignored it since
it's labeled as 2*m*...

Tim

Sorry, not my schematic and i did not look carefully: 2 milliohms is
absurd in a high voltage application

It's amazing how many really terrible schematics you can find on the
web. Many are hilarious. Somebody should do a collection of the, umm,
best.

John

"John Larkin" wrote in
message ...
It's amazing how many really terrible schematics you can find on the
web. Many are hilarious. Somebody should do a collection of the, umm,
best.

I suppose AoE3 will have an all-new set of "guess the fail" circuits.

What's terrible is the high PageRank on some of them. Google "high
voltage generator", this comes up:
http://www.repairfaq.org/sam/hvinvert.htm
Yuck, 2N3055s. Not even biased correctly. At least it'll run. This one
won't.
http://www.hackerbotlabs.com/tag/tl494/
Astonishingly it's an Instructable. How disappointing.

Tim

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

John Larkin wrote:
On Sun, 15 Aug 2010 00:24:10 -0700, Robert Baer
wrote:

The diode across the E-B junction of Q1 was added, mostly to prevent
zenering and then beta reduction.
D1 is removed for the waveforms seen; it clamps the negative swing
seen at V3 (and the +20V supply current increases with reduced HV output).
The question is, if the voltage on C5 is changed from about +10V to
+50V, that negative swing DOES NOT change, but the positive swing of Vc
does.
Can anyone explain how and why?

This looks like it's operating as a forward converter, and it looks to
me like the transformer is saturating. If that's true, it would work
better if the ON time of Q1 were reduced.

If it's saturating, that would explain why the flyback voltage
(negative spike at TP2) isn't changing as the C5 voltage changes.

John



You nailed it!
The "on" time of Q1 was way too much - found that R2 did not exist.
Did all of the following improvements: made R2=33K, made R1=50K,
permanently removed D1 as it's clamping of Q1 collector swing made
little difference other than increasing supply current.
Need to change output to FWD to get the added advantage of that
negative swing.
Now get about 1.5KV with 120V supply (R5 zero) and zero saturation as
confirmed with current probe.

Fred Bartoli wrote:
Robert Baer a écrit :
John Larkin wrote:
On Sun, 15 Aug 2010 00:24:10 -0700, Robert Baer
wrote:

The diode across the E-B junction of Q1 was added, mostly to
prevent zenering and then beta reduction.
D1 is removed for the waveforms seen; it clamps the negative swing
seen at V3 (and the +20V supply current increases with reduced HV
output).
The question is, if the voltage on C5 is changed from about +10V
to +50V, that negative swing DOES NOT change, but the positive swing
of Vc does.
Can anyone explain how and why?

This looks like it's operating as a forward converter, and it looks to
me like the transformer is saturating. If that's true, it would work
better if the ON time of Q1 were reduced.

If it's saturating, that would explain why the flyback voltage
(negative spike at TP2) isn't changing as the C5 voltage changes.

John



Ahh...will check that out; thanks.

It's more like Q1 is desaturating: look how vc gets back up to 20V at
t=200us while Q1 is still driven "hard" Ib = 140uA with a given 40-160
HFE range for the 2N3439... That makes for about 15mA max collector
current.

Checking the +20V current will sort that out.


T1 was saturating; now fixed - see other reply.

John Larkin wrote:
On Sun, 15 Aug 2010 23:50:59 -0700, Robert Baer
wrote:

Tim Williams wrote:
"John Larkin" wrote in
message ...
Note the 2M output resistor!
That's supposed to be 2M? I was a bit confused and just ignored it since
it's labeled as 2*m*...

Tim

Sorry, not my schematic and i did not look carefully: 2 milliohms is
absurd in a high voltage application

It's amazing how many really terrible schematics you can find on the
web. Many are hilarious. Somebody should do a collection of the, umm,
best.

John



At least, with your helpful comments, i managed to get it working
reasonably well.
At 50V supply (C5 voltage), get 580V no load and 480V 10Meg load; not
too bad - and supply current was roughly 1mA (i and i mean roughly as
the PS i used has a crude current meter with +/- 1mA resolution).

Tim Williams wrote:
"John Larkin" wrote in
message ...
It's amazing how many really terrible schematics you can find on the
web. Many are hilarious. Somebody should do a collection of the, umm,
best.

I suppose AoE3 will have an all-new set of "guess the fail" circuits.

What's terrible is the high PageRank on some of them. Google "high
voltage generator", this comes up:
http://www.repairfaq.org/sam/hvinvert.htm
Yuck, 2N3055s. Not even biased correctly. At least it'll run. This one
won't.
http://www.hackerbotlabs.com/tag/tl494/
Astonishingly it's an Instructable. How disappointing.

Tim

Only one of the four "pictures" became visible before the "feed" died
(dial-up does tend to kill flash junk).
Oh, well - this one is better that way.

John Larkin wrote:

On Sun, 15 Aug 2010 23:50:59 -0700, Robert Baer
? wrote:

?Tim Williams wrote:
?? "John Larkin" ? wrote in
?? message ...
??? Note the 2M output resistor!
??
?? That's supposed to be 2M? I was a bit confused and just ignored it since
?? it's labeled as 2*m*...
??
?? Tim
??
? Sorry, not my schematic and i did not look carefully: 2 milliohms is
?absurd in a high voltage application

It's amazing how many really terrible schematics you can find on the
web. Many are hilarious. Somebody should do a collection of the, umm,
best.


You offered to pay for the hosting of a website a while back. As
long as the number of submissions is reasonable, I'm willing to set up
the website. Post the schematic, and let people point out what is wrong
with it.

Startlogic.com & Ipower.com both have reasonably priced plans at less
than $10 a month.

Michael A. Terrell wrote:
John Larkin wrote:
On Sun, 15 Aug 2010 23:50:59 -0700, Robert Baer
? wrote:

?Tim Williams wrote:
?? "John Larkin" ? wrote in
?? message ...
??? Note the 2M output resistor!
??
?? That's supposed to be 2M? I was a bit confused and just ignored it since
?? it's labeled as 2*m*...
??
?? Tim
??
? Sorry, not my schematic and i did not look carefully: 2 milliohms is
?absurd in a high voltage application

It's amazing how many really terrible schematics you can find on the
web. Many are hilarious. Somebody should do a collection of the, umm,
best.


You offered to pay for the hosting of a website a while back. As
long as the number of submissions is reasonable, I'm willing to set up
the website. Post the schematic, and let people point out what is wrong
with it.

Startlogic.com & Ipower.com both have reasonably priced plans at less
than $10 a month.
Via GoDaddy (preferred) and *NOT* (may i swear) EarthRink which has
cheated in the past by double billing and attempted fraud by billing
closed credit cards.
Give me an address and preferred "pay to" and i should be able to
afford a year's fee in the $100-200 region near the end of this month.

Michael A. Terrell wrote:
John Larkin wrote:
On Sun, 15 Aug 2010 23:50:59 -0700, Robert Baer
? wrote:

?Tim Williams wrote:
?? "John Larkin" ? wrote in
?? message ...
??? Note the 2M output resistor!
??
?? That's supposed to be 2M? I was a bit confused and just ignored it since
?? it's labeled as 2*m*...
??
?? Tim
??
? Sorry, not my schematic and i did not look carefully: 2 milliohms is
?absurd in a high voltage application

It's amazing how many really terrible schematics you can find on the
web. Many are hilarious. Somebody should do a collection of the, umm,
best.


You offered to pay for the hosting of a website a while back. As
long as the number of submissions is reasonable, I'm willing to set up
the website. Post the schematic, and let people point out what is wrong
with it.

Startlogic.com & Ipower.com both have reasonably priced plans at less
than $10 a month.
Send me a bill or request for funds not in excess of $200 this month
as well as an estimate as to how much more may be required.
Since i am Socially InSecure, i can do only so much a month - which
varies according to expenses for weird things like food.