Re: PWM Timing Causing Shoot-thru
May,
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I don't know if we will see your updated file with the missing LTspice symbol, or if you consider the problem to be solved already.
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But I want to mention that your signals HCF and LCF did not look right.? In contrast with the other two pairs which have no overlap, the HCF and LCF pair have tons of overlap.? I think maybe you forgot to invert one of them.? Maybe that is correct, but it looks funny when compared with the other two pairs.
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Andy
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Re: 3 Phase Voltage Sense model
Larry,
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Here is an actual mistake, and the likely cause of the problem you have.? The pin-order of the symbol does not match the pin-order of the included netlist model.
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Symbol's pin-order:? Neutral VinA VinB VinC VoutA VoutB VoutC
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Subcircuit's pin-order:? VinA VinB VinC Neutral VoutA VoutB VoutC
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That needs to be corrected.? Edit either the symbol (.asy) file or the model (.sub) file.
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Andy
?
?
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Re: 3 Phase Voltage Sense model
Larry,
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Here are some issues to comment on:
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(1)? Your original schematic (3Phase_Voltage_Sense_circuit.asc) leaves the Neutral net floating.? Why?? Did you really want it to float like that?? Also, do you want it grounded in the final schematic?? If nothing else, it is different.
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(2)? The symbol you created (3Phase_Voltage_Sense.asy) is set up with incorrect properties.? It should have Symbol Type = Cell, but you left it with Symbol Type = Block, which is correct only for calling a lower-level schematic, not a netlist file.? Fortunately LTspice seems to handle it anyway in spite of the wrong property.
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(3)? Your final schematic (3Phase_Voltage_Sense_Test.asc) should not have ".inc 3Phase_Vsense.sub" because the symbol file already includes that netlist file.? It does not actually hurt because the end result is that the subcircuit file is included twice.? But it's not a good idea to do that because it might later create problems.
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I think none of these issues causes the problem you have, but I want to mention them anyway.
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Andy
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?
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Locked
Re: Windows XP installation disk
Off-topic.? And it suggests it is not legal.
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This topic is closed.? No replies, please.
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This group is about LTspice.
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Locked
Windows XP installation disk
Does anyone have a Windows XP install disk they could give or sell me? ?Or a copy with the password decrypted.
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I need a pukka XP machine to run the software I wrote myself in da last Millenium. ?Yes. ?I've tried the various Virtual machines but none of them give me the functionality I need. ?To put this into perspective, I run a DOS window under Win 98 on the XP machine.
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Machines that have XP drivers are all more than 10 yrs old. ?I found one but I lent my pukka XP install disc to a friend who promptly lost it?? ?
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Re: Weird results DC operating point for Tube amplifier
You're correct.
Le 20/02/2025 à 23:20, Andy I via
groups.io a écrit?:
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Show quoted text
On Thu, Feb 20, 2025 at 12:17 PM, Jerry Lee Marcel wrote:
BTW, source-follower it is not. It's actually a
common-source stage.
A source fiollower has about unity gain, this common-source
has about 15dB gain.
No, it is a source follower.? Its voltage gain is unity.? Input
applied to gate, output from source pin.? Almost the same output
voltage, but shifted 4.2 V lower.
?
The overall
circuit has voltage gain (~23 dB), but all of that comes from
the 12AU7, in its common-cathode configuration.
?
I wonder why you saw only 15 dB gain, and why you saw that in
just the MOSFET.
?
Not that the following has any significance - but I vaguely
recall reading about operating valves (vacuum tubes) at much
lower than "normal" anode voltages.? ?There were specialized
miniature valves designed for it.? But it was also applied to
more traditional valves too, ones like the 12AU7 that are
capable of hundreds of volts.? It does not appear to be a
sure-fire way to generate distortion, as this simulation
demonstrates, if you trust the SPICE models.? I can't recall
what were the advantages (if any) of using such low voltages -
other than easier battery power.? Lower noise?? ?Longer life?? I
dunno.
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Andy
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CD4000_v(65).lib with syntax error messages updated to CD4000_v(65a).lib
hi
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I've corrected and uploaded CD4000_v(65a).lib
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The only corrections made were to the td1,td2,td4 equations used in CD4008B sub circuit.
The unbalanced braces/parenths caused syntax error messages in LTspice 24.1.4
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eetech00
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Re: Weird results DC operating point for Tube amplifier
Oh, I get that by putting a 10cm long
unobtanium tube over the headphone cable.
On 2025-02-20 22:22, Andy I via
groups.io wrote:
On Thu, Feb 20, 2025 at 12:32 PM, John Woodgate wrote:
There really isn't any
point in criticizing the design. It's deliberately weird.
An LM386 makes a good headphone amplifier, but it might be
difficult to sell for $130.
Yeah, but then it would not have that "tube sound".
?
?
--
OOO - Own Opinions only
If something is true:
* as far as we know - it's science
*for certain - it's mathematics
*unquestionably - it's religion
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Re: Weird results DC operating point for Tube amplifier
I have to confess that I was misled by this at
an early age, about 13 I think.? The valve doesn't know what the
supply voltage is with zero signal. It only knows the voltage
between anode and cathode, which can be quite small, yet even a
triode still can give gain. I simply didn't believe a DAC32
would work with a 470k anode load, so I used 4.7k, which gave
hardly any gain. What this low Vak does, of course, is limit the
maximum output signal amplitude, but if only a volt or two is
required, there is no problem.
OT observation: With small-signal pentodes,
such as EF33 or EF50, very low anode and g2 voltages can be
used, with megohm values of feed resistors, giving very high
gain.
On 2025-02-20 22:20, Andy I via
groups.io wrote:
Not that the
following has any significance - but I vaguely recall reading
about operating valves (vacuum tubes) at much lower than "normal"
anode voltages.?
--
OOO - Own Opinions only
If something is true:
* as far as we know - it's science
*for certain - it's mathematics
*unquestionably - it's religion
|
Re: Interpreting Noise Simulation Results
manauo,
?
Almost all the simulated noise in your circuit comes from the circuit itself.? If there was noise in the sources driving it (V1, V2, V5, V6), it is not present in the simulation.? Those voltage sources are noise-free.? Therefore, adding high-pass filter capacitors to reduce noise from the source, does not do you any good, unless the source itself had noise.? I think the only parts behind the HPF that generate any noise in this simulation, are the 0.6 ohm resistors, R9, R10, R21, and R22.? (Also the Rser of L1-L4.)? That's about the only benefit to be had from adding those capacitors.
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On top of that, there is the increase in noise caused by making the source impedance (connected to the transistor bases) larger.? That is likely why you saw the noise density going up instead of down.
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Not many people use SPICE's .NOISE analysis.? Consequently, many device models either lack the parameters needed to simulate it well, or the parameter values are badly wrong.? That was especially true of the JFET models that came with LTspice.? LTspice got those models from the company Linear Systems (not to be confused with Linear Technology Corp.), but someone at Linear Systems had inadvertently messed up their own SPICE models before giving them to LTC for inclusion in LTspice.? If I remember correctly, the mistake was 5 orders of magnitude (!) and applied to every one of their JFET models.? Fortunately your circuit has only BJTs, no JFETs, so it might be OK.? Should be OK for comparative simulations.
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Andy
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Re: Weird results DC operating point for Tube amplifier
Any tube sound this design gives you is weird tube sound. ?
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From: [email protected] <[email protected]> On Behalf Of Andy I via groups.io
Sent: Thursday, February 20, 2025 5:23 PM
To: [email protected]
Subject: Re: [LTspice] Weird results DC operating point for Tube amplifier? On Thu, Feb 20, 2025 at 12:32 PM, John Woodgate wrote: There really isn't any point in criticizing the design. It's deliberately weird. An LM386 makes a good headphone amplifier, but it might be difficult to sell for $130.
Yeah, but then it would not have that "tube sound".
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Re: PWM Timing Causing Shoot-thru
On Thu, Feb 20, 2025 at 04:20 PM, May wrote:
It is missing the symbol for IR2110.? The missing file is ir2110.asy.? Please add it to your .zip file and re-upload it.
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Additionally, probing the gates of the FETs shows that there is somehow overlap in the HI and LO drive signals, despite my attempts to tune the voltage sources I am using to generate the PWM signals.
That is likely to be a cause of shoot-through current.
?
I am not sure if the shoot-through is an artifact of LTSpice or if I am simply wrong with how I have set the PWMs up.
I think it is unlikely to be an LTspice artifact, but something in the models might be responsible.? Large MOSFETs can have significant input (gate) capacitance which can mess things up.? If you probe the signals you generated, do they seem right or do they have the wrong overlap?
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Andy
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Re: PWM Timing Causing Shoot-thru
Bruce,
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Based on your comments, I think I have been able to successfully utilize the SD pin of the IR2110 to eliminate the shoot-through I was seeing.
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Thanks so much!!
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-May
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Re: Weird results DC operating point for Tube amplifier
On Thu, Feb 20, 2025 at 12:32 PM, John Woodgate wrote:
There really isn't any point in criticizing the design. It's deliberately weird. An LM386 makes a good headphone amplifier, but it might be difficult to sell for $130.
Yeah, but then it would not have that "tube sound".
?
?
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Re: Weird results DC operating point for Tube amplifier
On Thu, Feb 20, 2025 at 12:17 PM, Jerry Lee Marcel wrote:
BTW, source-follower it is not. It's actually a common-source stage.
A source fiollower has about unity gain, this common-source has about 15dB gain.
No, it is a source follower.? Its voltage gain is unity.? Input applied to gate, output from source pin.? Almost the same output voltage, but shifted 4.2 V lower.
?
The overall circuit has voltage gain (~23 dB), but all of that comes from the 12AU7, in its common-cathode configuration.
?
I wonder why you saw only 15 dB gain, and why you saw that in just the MOSFET.
?
Not that the following has any significance - but I vaguely recall reading about operating valves (vacuum tubes) at much lower than "normal" anode voltages.? ?There were specialized miniature valves designed for it.? But it was also applied to more traditional valves too, ones like the 12AU7 that are capable of hundreds of volts.? It does not appear to be a sure-fire way to generate distortion, as this simulation demonstrates, if you trust the SPICE models.? I can't recall what were the advantages (if any) of using such low voltages - other than easier battery power.? Lower noise?? ?Longer life?? I dunno.
?
Andy
?
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Re: Interpreting Noise Simulation Results
Yes, an RC high pass filter on the input
will increase the noise. Although the capacitor doesn't itself add
any noise, it causes the effective input noise voltage to
increase, because:
Vn(tot) = √(En^2 + (In/2/pi/Cser)^2)
..where: En = I/P noise voltage density, and In = I/P noise
current density (neglecting the source resistance noise, which
often you can't do)
Remember also: "No attenuation before gain".
I should also mention (without seeing your schematic), that many
of the devices in the LTspice standard libraries don't have
realistic noise parameters, especially when it comes to 1/f noise.
--
Regards,
Tony
On 20/02/2025 20:17, manauo via
groups.io wrote:
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Show quoted text
I don't have much experience using LTSPICE for noise
simulations, and I'm having trouble understanding some of the
results I'm getting. I'm investigating an amplifier circuit
(file "Amplifier Noise" uploaded to files/Temp).
?
The amplifier is a cascode differential pair, signal
frequency is 1MHz. Currently the circuit has no filtering
besides the inherent roll-off at high frequency. I'm
investigating whether adding AC coupling capacitors to the input
to filter low-frequency noise can improve the performance. The
inductance/resistance in series with each input represents the
output impedance of the previous stage.
?
When I simulate the original circuit with no coupling
capacitors, the result seems reasonable - relatively flat, input
noise is a fraction of the output noise. However when I simulate
the proposed circuit with coupling capacitors I don't understand
the result.
?
The input noise balloons at low frequencies - the frequency
range that the HPF of the capacitor is supposed to reduce, is
now much greater. The output noise is lower in terms of total
integrated noise, but still has an increased magnitude at low
frequency compared to the original.
?
The decrease in total output noise is coming from a decrease
in the high frequency noise, which makes sense because the
inductance of the source impedance and the base pull-down
resistor form an RL LPF. But the capacitor does not seem to be
reducing LF noise, even though an AC sweep shows the expected
HPF behavior.
?
Am I misinterpreting the results somehow? How is adding a
high-pass filter at the input increasing noise at the low
frequencies that it is supposed to be attenuating? What am I
missing about noise simulations?
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Re: PWM Timing Causing Shoot-thru
You need to find a strategy to enforce some amount of deadtime between the signals. Tuning is not going to do the job unless it is predictable and repeatable, Analog methods tend to be unreliable.
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BRUCE108
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PWM Timing Causing Shoot-thru
I am having some trouble getting the timing right on my PWM drive signals. What tells me my timing is wrong is the fact that I am seeing what appears to be shoot-through periodically.
?
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Additionally, probing the gates of the FETs shows that there is somehow overlap in the HI and LO drive signals, despite my attempts to tune the voltage sources I am using to generate the PWM signals.
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Any help is appreciated; I am not sure if the shoot-through is an artifact of LTSpice or if I am simply wrong with how I have set the PWMs up.
?
Thanks,
-May
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Re: Interpreting Noise Simulation Results
At low frequencies, the capacitor's impedance is quite high. the
noise current generated by the active stages circulates in this
increased impedance, resulting in an increasing voltage.
Le 20/02/2025 à 20:17, manauo via
groups.io a écrit?:
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Show quoted text
Hello,
?
I don't have much experience using LTSPICE for noise
simulations, and I'm having trouble understanding some of the
results I'm getting. I'm investigating an amplifier circuit
(file "Amplifier Noise" uploaded to files/Temp).
?
The amplifier is a cascode differential pair, signal
frequency is 1MHz. Currently the circuit has no filtering
besides the inherent roll-off at high frequency. I'm
investigating whether adding AC coupling capacitors to the input
to filter low-frequency noise can improve the performance. The
inductance/resistance in series with each input represents the
output impedance of the previous stage.
?
When I simulate the original circuit with no coupling
capacitors, the result seems reasonable - relatively flat, input
noise is a fraction of the output noise. However when I simulate
the proposed circuit with coupling capacitors I don't understand
the result.
?
The input noise balloons at low frequencies - the frequency
range that the HPF of the capacitor is supposed to reduce, is
now much greater. The output noise is lower in terms of total
integrated noise, but still has an increased magnitude at low
frequency compared to the original.
?
The decrease in total output noise is coming from a decrease
in the high frequency noise, which makes sense because the
inductance of the source impedance and the base pull-down
resistor form an RL LPF. But the capacitor does not seem to be
reducing LF noise, even though an AC sweep shows the expected
HPF behavior.
?
Am I misinterpreting the results somehow? How is adding a
high-pass filter at the input increasing noise at the low
frequencies that it is supposed to be attenuating? What am I
missing about noise simulations?
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Re: Weird results DC operating point for Tube amplifier
That is not the subject.
The subject is that they try to justify their quirky "design"
with objective arguments.
Enough said now.
Le 20/02/2025 à 19:45, John Woodgate a
écrit?:
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Show quoted text
RE; Yes, what? You asked, 'Or can they?',
and the answer is, 'Yes, easily'. Well, of course Bravo
wouldn't give figures that showed less than excellent
performance. The THD with 33 ohm load is admitted to be rather
high, and we don't know what the output voltage or power was
at that THD. That is why I gave the two pairs of amplifier
figures as an example.
On 2025-02-20 18:14, Jerry Lee Marcel
via groups.io wrote:
Le 20/02/2025 à 17:33, John
Woodgate a écrit?:
Yes, easily.
Yes what?
Consider, for example, these two
amplifiers:
a) Output power 30 W, THD 0.1%
b) Output power 35 W, THD 5.2%
Which would you buy?
I don't care, but Bravo Audio seems to care
about figures that are long accepted as performance
indicators.
They are the same amplifier. Similar
games are played with signal-to-noise ratio and frequency
response.
On 2025-02-20 16:05, Jerry Lee
Marcel via groups.io wrote:
Still they are publishing specifications that pertain to
typical audio performance, such as frequency response and
THD. They can't combine both quirkiness and normality.
Or can they?
Typical "I designed it that way because I could".
IMO it justifies disdain.
Le 20/02/2025 à 16:55, John
Woodgate a écrit?:
I suspect that the weirdness is
intentional. Weird designs have existed from? the
earliest day of DIY radio receivers, before
'electronics'? was in the dictionary. I recall a
report of a circuit that had the 2 V lead-acid cell
apparently in series with the antenna circuit.
Objective performance measurements are typically not
to be applied to such designs. DO a web search for
'Bravo Audio reviews'.
On 2025-02-20 15:36, Jerry
Lee Marcel via groups.io wrote:
Le 20/02/2025 à 15:27,
Carlo a écrit?:
On Thu, Feb 20, 2025 at 05:40 AM, Andy I wrote:
There is some feedback from the audio
signal into the heater voltage. Was that
intentional?? Or just an undesirable side-effect??
I don't expect it would have very much effect on
the heater's temperature (and from there to the
triode's characteristics), but it looks
undesirable to me. Should there be filtering?
Sorry, are you asking whether the audio signal
feedback into the heater voltage comes from a design
intentional choice ? Actually I don't know since I
took it from the schematic of a commercial audio
amplifier (Bravo Ocean).
It's extremely unlikely.
Heater temperature varies extremely slowly compared to
audio signals.
It could result in distortion at very very low
frequencies, definitely out of the audio band.
Now this design is weird from the start. Choosing to
power a tube circuit from 24VDC is a major flaw, unless
the goal is to create distortion.
--
OOO - Own Opinions only If something is true: * as far
as we know - it's science *for certain - it's
mathematics *unquestionably - it's religion
--
OOO - Own Opinions only If something is true: * as far as we
know - it's science *for certain - it's mathematics
*unquestionably - it's religion
--
OOO - Own Opinions only If something is true: * as far as we
know - it's science *for certain - it's mathematics
*unquestionably - it's religion
|
John Woodgate
Tony Casey