|
21/12/2014 14:59
I am pretty hopeless with, what to me, is a very complicated 7854. It
has 7A26, 7A19, 7B85 and a 7B54 plug in array. I have a venerable old
Farnell power supply that has just killed some CMOS devices. I
suspected my circuit building skills for a while, then realised one
output of this series / parallel/ independent dual output PS was
spiking over the set 5V badly. I can see from the scope display it's
going to at least 10V when the power switch for the side in use is
turned on. The othwer side of the supply does not appear to spike at
all. What I do not know how to do, assuming it's possible, is to
get a trace displayed and held, showing just how bad and how fast this
spike is. Could anyone describe in simple and detailed terms how I
might acquire a trace? Thanks. I got the scope for a song with its own
PS issues which are fixed, but it's probably a lot more sophisticated
than I will ever need, in reality!
--
Best Regards,
Chris Wilson.
mailto: chris@...
|
On 12/21/2014 09:05 AM, Chris Wilson chris@... [TekScopes] wrote: has 7A26, 7A19, 7B85 and a 7B54 plug in Is that a 7B87 timebase plugin rather than 7B54? to look at your PS spikes you can use the 7854 in analog scope mode, no memory storing, 7A26 in DC mode, 2 Volts per division, triggering normal, trigger knob fully counterclockwise, X10 probe with readout change so 2 Volts per division is for real, + triggering, and move the trigger level up clockwise until it triggers on something at 5 Volts showing a frequent trigger and thus bright line at the DC level volts. Then move trigger level up some more to get a more faint display of spike triggers. Then increase the sweep rate to see detail. John
|
Sorry, a typo, I read my poor handwriting of 7854 (the mainframe
itself) as a 7B54! You are quite right, the other plugin is a 7B7!
Apologies. Thank you very much for the clear and detailed
instruction, but one question, was I clear in explaining this spike
is a single one, just at turn on? Not an ongoing event like ripple? I
will try your instructions and report back, thanks again. I was
expecting to have to use the storage facility, this looks a lot more
straightforward.
Best Regards,
Chris Wilson. 2E0ILY
toggle quoted message
Show quoted text
On 12/21/2014 09:05 AM, Chris Wilson chris@... [TekScopes] wrote:
has 7A26, 7A19, 7B85 and a 7B54 plug in Is that a 7B87 timebase plugin rather than 7B54? to look at your PS spikes you can use the 7854 in analog scope mode, no
memory storing, 7A26 in DC mode, 2 Volts per division, triggering normal,
trigger knob fully counterclockwise,
X10 probe with readout change so 2 Volts per division is for real, + triggering,
and move the trigger level up clockwise until it triggers on
something at 5 Volts showing a frequent
trigger and thus bright line at the DC level volts. Then move trigger level up some
more to get a more faint display of spike triggers. Then increase the sweep rate to
see detail. John
|
7B7 new typo Chris? A 7B87 would be nicest for single sweep records with pretrigger, so you can view the leading edge of the spike and probably the whole spike. Things also depend on the time span of the spike, so on the time/div setting for a good display of the spike. Fast sweep rates can not be recorded in a single sweep. Details for a 7B87 can better wait I think until it's sure that you have one.
You can set the trigger level to above +5 V like John suggested and then record a single sweep. You might also close the curtains and dim the lights and hope you see the real time single sweep. But you might miss the leading edge or more of the spike. Then you might try a delaying/delayed time base setup. Set the 7B85 for triggering at about +2 V (so for triggering immediately when you switch on the power) and slow enough speed to see the spike occurring also. Next set the time bases for delayed sweep and "starts after delay time". Choose a proper speed for the delayed sweep and a proper delay time at the 7B85 to catch the spike (lights dimmed even further...).
Of course for the PS this means power off and on many times.
Albert
---In TekScopes@..., <chris@...> wrote :
Sorry, a typo, I read my poor handwriting of 7854 (the mainframe
itself) as a 7B54! You are quite right, the other plugin is a 7B7!
Apologies. Thank you very much for the clear and detailed
instruction, but one question, was I clear in explaining this spike
is a single one, just at turn on? Not an ongoing event like ripple? I
will try your instructions and report back, thanks again. I was
expecting to have to use the storage facility, this looks a lot more
straightforward.
Best Regards,
Chris Wilson. 2E0ILY
toggle quoted message
Show quoted text
On 12/21/2014 09:05 AM, Chris Wilson chris@... mailto:chris@... [TekScopes] wrote: >> has 7A26, 7A19, 7B85 and a 7B54 plug in > Is that a 7B87 timebase plugin rather than 7B54? > to look at your PS spikes you can use the 7854 in analog scope mode, no > memory storing, 7A26 in DC mode, 2 Volts per division, triggering normal, > trigger knob fully counterclockwise, > X10 probe with readout change so 2 Volts per division is for real, + triggering, > and move the trigger level up clockwise until it triggers on > something at 5 Volts showing a frequent > trigger and thus bright line at the DC level volts. Then move trigger level up some > more to get a more faint display of spike triggers. Then increase the sweep rate to > see detail. > John
|
On 12/21/2014 10:20 AM, Chris Wilson chris@... [TekScopes] wrote: this spike
is a single one, just at turn on? Not an ongoing event like ripple? I missed that. What I said could still get you set up to see it at each pressing of the on switch... Then, like Albert says. So, how did you first notice the existence of this spike? John
|
Chris: You need to be careful with most power supplies. I have great respect for HP power supplies, but even theirs generate a wopping voltage surge the moment they are turned-on. If I had the HP power supply connected to TTL circuitry, the momentary voltage spike of 30 volts would certainly damage the 5-volt integrated circuits in the test circuit. I hate having "walking wounded" circuitry. The HP power supply even generates these spikes if the voltage control is set for zero volts. So, the best thing to do is power-up the bench supply and accurately set its output voltage before attaching the test leads to your circuit. Gary On Dec 21, 2014 7:05 AM, "Chris Wilson chris@... [TekScopes]" < TekScopes@...> wrote:
21/12/2014 14:59
I am pretty hopeless with, what to me, is a very complicated 7854. It
has 7A26, 7A19, 7B85 and a 7B54 plug in array. I have a venerable old
Farnell power supply that has just killed some CMOS devices. I
suspected my circuit building skills for a while, then realised one
output of this series / parallel/ independent dual output PS was
spiking over the set 5V badly. I can see from the scope display it's
going to at least 10V when the power switch for the side in use is
turned on. The othwer side of the supply does not appear to spike at
all. What I do not know how to do, assuming it's possible, is to
get a trace displayed and held, showing just how bad and how fast this
spike is. Could anyone describe in simple and detailed terms how I
might acquire a trace? Thanks. I got the scope for a song with its own
PS issues which are fixed, but it's probably a lot more sophisticated
than I will ever need, in reality!
--
Best Regards,
Chris Wilson.
mailto: chris@...
|
Hi again John. I noticed it after I blew two ATmega chips, and two DDS
oscillator boards! I initially thought I'd done something wrong in the
assembly of the boards, then finding nothing I had to look elsewhere.
I haven't mastered the 7854 yet, so any view of the spikes have been
very transient. Using my 100MHz USB scope I get the two patterns as
linked. The clean one stopping dead on 5V is from the LH section of
the dual supply. The one that ramps right up before slowly ramping
down to 5V again is the RH section. Two guesses which I was using....
:(
To Gary Bosworth: Thanks Gary, I see exactly what you mean! I think
I'll build a couple of small boxes with a modern regulators in them
for TTL stuff, 3.3 and 5V. It took me while, being a beginner, to
realise it wasn't my circuit building skills, but the damned power
supply! Thanks.
Albert: I will persevere with the 7854, I need to get the hang of it
much better. Thank you.
Best Regards,
Chris Wilson. 2E0ILY
|
Wow I haven't seen that in my supplies at all. On turn-on they nicely come up to the set voltage with virtually no overshoot.
Peter
toggle quoted message
Show quoted text
On 12/21/2014 1:28 PM, Gary Robert Bosworth grbosworth@... [TekScopes] wrote:
Chris:
You need to be careful with most power supplies. I have great respect for
HP power supplies, but even theirs generate a wopping voltage surge the
moment they are turned-on. If I had the HP power supply connected to TTL
circuitry, the momentary voltage spike of 30 volts would certainly damage
the 5-volt integrated circuits in the test circuit. I hate having "walking
wounded" circuitry. The HP power supply even generates these spikes if the
voltage control is set for zero volts. So, the best thing to do is
power-up the bench supply and accurately set its output voltage before
attaching the test leads to your circuit.
Gary
On Dec 21, 2014 7:05 AM, "Chris Wilson chris@... [TekScopes]" <
TekScopes@...> wrote:
21/12/2014 14:59
I am pretty hopeless with, what to me, is a very complicated 7854. It
has 7A26, 7A19, 7B85 and a 7B54 plug in array. I have a venerable old
Farnell power supply that has just killed some CMOS devices. I
suspected my circuit building skills for a while, then realised one
output of this series / parallel/ independent dual output PS was
spiking over the set 5V badly. I can see from the scope display it's
going to at least 10V when the power switch for the side in use is
turned on. The othwer side of the supply does not appear to spike at
all. What I do not know how to do, assuming it's possible, is to
get a trace displayed and held, showing just how bad and how fast this
spike is. Could anyone describe in simple and detailed terms how I
might acquire a trace? Thanks. I got the scope for a song with its own
PS issues which are fixed, but it's probably a lot more sophisticated
than I will ever need, in reality!
--
Best Regards,
Chris Wilson.
mailto: chris@...
|
I assume you're going with digital storage, single-sweep, using the 7854. A very simple way to see the whole works is to rig a multipole switch in series with the PS under test to control its line voltage input. Then set up a low-voltage trigger circuit with one of the other switch poles, to externally trigger the scope. Leave the supply's switch on, and flip the line power with the added switch - the external trigger will always lead the power supply's output events, so you should be able to capture everything of interest with a conventional (non-7B87) sweep. Be sure to set up the triggering signal and settings to start on the first instance of switch contact - the bounce should be no problem at the sweep rates of interest. You can also see what happens on power-down, by reversing the trigger slope setting.
Ed
|
Hi Chris,
Do I read the RH waveform correct as taken with 10 ms/div? Then I would call it overshoot rather than a spike. Should be very easy to capture single-sweep with the 7B85 when you set the trigger level just slightly above zero. I also think that this is not normal supply behavior and has a simple cause somewhere inside. With very short spikes the situation might be far more complicated. Maybe you should also check the load regulation of the RH supply when the load changes suddenly.
Albert
======
|
I am not even sure what a 7B54 is.
The 7B87 is needed to capture single shot events on a 7854. Without the 7B87 it
will be very difficult to capture the power supply turn on surge. With the 7B87
it will be trivial.
toggle quoted message
Show quoted text
On 21 Dec 2014 09:12:25 -0800, you wrote: 7B7 new typo Chris? A 7B87 would be nicest for single sweep records with pretrigger, so you can view the leading edge of the spike and probably the whole spike. Things also depend on the time span of the spike, so on the time/div setting for a good display of the spike. Fast sweep rates can not be recorded in a single sweep. Details for a 7B87 can better wait I think until it's sure that you have one.
You can set the trigger level to above +5 V like John suggested and then record a single sweep. You might also close the curtains and dim the lights and hope you see the real time single sweep. But you might miss the leading edge or more of the spike. Then you might try a delaying/delayed time base setup. Set the 7B85 for triggering at about +2 V (so for triggering immediately when you switch on the power) and slow enough speed to see the spike occurring also. Next set the time bases for delayed sweep and "starts after delay time". Choose a proper speed for the delayed sweep and a proper delay time at the 7B85 to catch the spike (lights dimmed even further...).
Of course for the PS this means power off and on many times.
Albert
---In TekScopes@..., <chris@...> wrote :
Sorry, a typo, I read my poor handwriting of 7854 (the mainframe
itself) as a 7B54! You are quite right, the other plugin is a 7B7!
Apologies. Thank you very much for the clear and detailed
instruction, but one question, was I clear in explaining this spike
is a single one, just at turn on? Not an ongoing event like ripple? I
will try your instructions and report back, thanks again. I was
expecting to have to use the storage facility, this looks a lot more
straightforward.
On 12/21/2014 09:05 AM, Chris Wilson chris@... mailto:chris@... [TekScopes] wrote:
has 7A26, 7A19, 7B85 and a 7B54 plug in Is that a 7B87 timebase plugin rather than 7B54? to look at your PS spikes you can use the 7854 in analog scope mode, no
memory storing, 7A26 in DC mode, 2 Volts per division, triggering normal,
trigger knob fully counterclockwise,
X10 probe with readout change so 2 Volts per division is for real, + triggering,
and move the trigger level up clockwise until it triggers on
something at 5 Volts showing a frequent
trigger and thus bright line at the DC level volts. Then move trigger level up some
more to get a more faint display of spike triggers. Then increase the sweep rate to
see detail.
|
This issue crops up over on EEVblog. Lots of power supply designs have voltage
surge problems when starting up or shutting down. Professional power supplies
are usually designed to avoid this either inherently or with additional
circuits.
This is one of those places where a DSO and even a 7854 with 7B87 timebase are
invaluable.
toggle quoted message
Show quoted text
On Sun, 21 Dec 2014 10:28:12 -0800, you wrote: Chris:
You need to be careful with most power supplies. I have great respect for
HP power supplies, but even theirs generate a wopping voltage surge the
moment they are turned-on. If I had the HP power supply connected to TTL
circuitry, the momentary voltage spike of 30 volts would certainly damage
the 5-volt integrated circuits in the test circuit. I hate having "walking
wounded" circuitry. The HP power supply even generates these spikes if the
voltage control is set for zero volts. So, the best thing to do is
power-up the bench supply and accurately set its output voltage before
attaching the test leads to your circuit.
Gary
|
Hello, Some power supplies exhibit this bad habit when powered off. This is caused by the regulating circuit losing control but normally the design has provisions for avoiding that, either with the auxiliary power supply having enough reserve in the capacitors to be fully working until the main supply caps discharge and others have circuitry that shuts down the series transistors when the auxiliary drops. Similar tricks are used for the power up phase when needed and if they fail cause the described symptoms, and since this happens only on power up or power down it gets unnoticed most of the time until you begin to fry things. I never have seen any respectable commercial power supply doing these things unless it is faulty, but seen in several homemade designs. Regards, Ignacio EB4APL On 21/12/2014 a las 21:44, Peter Gottlieb hpnpilot@... [TekScopes] wrote:
Wow I haven't seen that in my supplies at all. On turn-on they nicely
come up
to the set voltage with virtually no overshoot.
Peter
On 12/21/2014 1:28 PM, Gary Robert Bosworth grbosworth@...
[TekScopes] wrote:
Chris:
You need to be careful with most power supplies. I have great
respect for
HP power supplies, but even theirs generate a wopping voltage surge the
moment they are turned-on. If I had the HP power supply connected to TTL
circuitry, the momentary voltage spike of 30 volts would certainly damage
the 5-volt integrated circuits in the test circuit. I hate having "walking
wounded" circuitry. The HP power supply even generates these spikes if the
voltage control is set for zero volts. So, the best thing to do is
power-up the bench supply and accurately set its output voltage before
attaching the test leads to your circuit.
Gary
On Dec 21, 2014 7:05 AM, "Chris Wilson chris@... [TekScopes]" <
TekScopes@...> wrote:
21/12/2014 14:59
I am pretty hopeless with, what to me, is a very complicated 7854. It
has 7A26, 7A19, 7B85 and a 7B54 plug in array. I have a venerable old
Farnell power supply that has just killed some CMOS devices. I
suspected my circuit building skills for a while, then realised one
output of this series / parallel/ independent dual output PS was
spiking over the set 5V badly. I can see from the scope display it's
going to at least 10V when the power switch for the side in use is
turned on. The othwer side of the supply does not appear to spike at
all. What I do not know how to do, assuming it's possible, is to
get a trace displayed and held, showing just how bad and how fast this
spike is. Could anyone describe in simple and detailed terms how I
might acquire a trace? Thanks. I got the scope for a song with its own
PS issues which are fixed, but it's probably a lot more sophisticated
than I will ever need, in reality!
--
Best Regards,
Chris Wilson.
mailto: chris@...
------------------------------------------------------------------------
Posted by: Peter Gottlieb <hpnpilot@...>
|
I find that completely unacceptable, and actually somewhat outrageous. A power supply is manufactured *intentionally* with this uncorrected?
I just went through all my bench supplies (HP 6002A, 6209B and BK Precision 1630) and a random selection of modular linear and switching supplies I have and found NONE with any overshoot. All that varied was the shape and speed of the curve to reach output voltage. The 6002A, like many others out there, have a settable OVP to prevent accidents, maybe you should get one of those modules to protect your projects.
Peter
toggle quoted message
Show quoted text
On 12/21/2014 5:55 PM, David davidwhess@... [TekScopes] wrote:
This issue crops up over on EEVblog. Lots of power supply designs have voltage
surge problems when starting up or shutting down. Professional power supplies
are usually designed to avoid this either inherently or with additional
circuits.
This is one of those places where a DSO and even a 7854 with 7B87 timebase are
invaluable.
On Sun, 21 Dec 2014 10:28:12 -0800, you wrote:
Chris:
You need to be careful with most power supplies. I have great respect for
HP power supplies, but even theirs generate a wopping voltage surge the
moment they are turned-on. If I had the HP power supply connected to TTL
circuitry, the momentary voltage spike of 30 volts would certainly damage
the 5-volt integrated circuits in the test circuit. I hate having "walking
wounded" circuitry. The HP power supply even generates these spikes if the
voltage control is set for zero volts. So, the best thing to do is
power-up the bench supply and accurately set its output voltage before
attaching the test leads to your circuit.
Gary
|
On home-made supplies I could believe this, but like you said, not in halfway decent commercial supplies, unless there's a fault.
Peter
toggle quoted message
Show quoted text
On 12/21/2014 6:08 PM, EB4APL eb4apl@... [TekScopes] wrote:
Hello,
Some power supplies exhibit this bad habit when powered off. This is
caused by the regulating circuit losing control but normally the design
has provisions for avoiding that, either with the auxiliary power supply
having enough reserve in the capacitors to be fully working until the
main supply caps discharge and others have circuitry that shuts down the
series transistors when the auxiliary drops. Similar tricks are used
for the power up phase when needed and if they fail cause the described
symptoms, and since this happens only on power up or power down it gets
unnoticed most of the time until you begin to fry things.
I never have seen any respectable commercial power supply doing these
things unless it is faulty, but seen in several homemade designs.
Regards,
Ignacio EB4APL
On 21/12/2014 a las 21:44, Peter Gottlieb hpnpilot@... [TekScopes]
wrote:
Wow I haven't seen that in my supplies at all. On turn-on they nicely
come up
to the set voltage with virtually no overshoot.
Peter
On 12/21/2014 1:28 PM, Gary Robert Bosworth grbosworth@...
[TekScopes] wrote:
Chris:
You need to be careful with most power supplies. I have great
respect for
HP power supplies, but even theirs generate a wopping voltage surge the
moment they are turned-on. If I had the HP power supply connected to TTL
circuitry, the momentary voltage spike of 30 volts would certainly damage
the 5-volt integrated circuits in the test circuit. I hate having "walking
wounded" circuitry. The HP power supply even generates these spikes if the
voltage control is set for zero volts. So, the best thing to do is
power-up the bench supply and accurately set its output voltage before
attaching the test leads to your circuit.
Gary
On Dec 21, 2014 7:05 AM, "Chris Wilson chris@... [TekScopes]" <
TekScopes@...> wrote:
21/12/2014 14:59
I am pretty hopeless with, what to me, is a very complicated 7854. It
has 7A26, 7A19, 7B85 and a 7B54 plug in array. I have a venerable old
Farnell power supply that has just killed some CMOS devices. I
suspected my circuit building skills for a while, then realised one
output of this series / parallel/ independent dual output PS was
spiking over the set 5V badly. I can see from the scope display it's
going to at least 10V when the power switch for the side in use is
turned on. The othwer side of the supply does not appear to spike at
all. What I do not know how to do, assuming it's possible, is to
get a trace displayed and held, showing just how bad and how fast this
spike is. Could anyone describe in simple and detailed terms how I
might acquire a trace? Thanks. I got the scope for a song with its own
PS issues which are fixed, but it's probably a lot more sophisticated
than I will ever need, in reality!
--
Best Regards,
Chris Wilson.
mailto: chris@...
----------------------------------------------------------
Posted by: Peter Gottlieb <hpnpilot@...>
|
I have a Heathkit IP-17 regulated HV power supply. The B+ potentiometer is noisy. When it is rotated, all sorts of voltages appear at the B+ output terminals. This is an undesirable characteristic. In contrast, I find that Power Designs made/makes some of the nicest power supplies. I have a 3650-S. The voltage knob rotates a variac and a potentiometer. V_ce of the pass transistors is more or less independent of the position of the voltage knob. Elegance. On Sun, Dec 21, 2014 at 5:55 PM, David davidwhess@... [TekScopes] < TekScopes@...> wrote:
This issue crops up over on EEVblog. Lots of power supply designs have
voltage
surge problems when starting up or shutting down. Professional power
supplies
are usually designed to avoid this either inherently or with additional
circuits.
This is one of those places where a DSO and even a 7854 with 7B87 timebase
are
invaluable.
On Sun, 21 Dec 2014 10:28:12 -0800, you wrote:
Chris:
You need to be careful with most power supplies. I have great respect for
HP power supplies, but even theirs generate a wopping voltage surge the
moment they are turned-on. If I had the HP power supply connected to TTL
circuitry, the momentary voltage spike of 30 volts would certainly damage
the 5-volt integrated circuits in the test circuit. I hate having "walking
wounded" circuitry. The HP power supply even generates these spikes if the
voltage control is set for zero volts. So, the best thing to do is
power-up the bench supply and accurately set its output voltage before
attaching the test leads to your circuit.
Gary
[Non-text portions of this message have been removed]
|
You may have some success squirting a good contact cleaner into the noisy pot. Caig (formerly known as Kramolin) works very well for me.
|
Gary Robert Bosworth
David Hess