REVIEW - Owon SDS7102 - A look at the SDS series from Owon

[TomC]

OK, TomC take your time that you are needing and I am here to measure whatever you want.

I prepare a work about AZ1094 circuit...it has a lot of interesting!

That'll be interesting!

Your PSU board is different from mine, so I attached images of where I think it'll be easiest to hook up the probes. CH1 should be on D8's anode, and CH2 on Q1's drain. Both ground leads to the Z-plate. Make sure the probes are set to X10 because the peak voltage at Q1's drain may be more than 400V with 230VAC mains. While the scope is running you'll see an image like #1, jumping up and down. When the baseline of the CH2 trace is level with the ground marker it is as closely referenced to the Z-plate ground as you can get. To get a capture like #2 I used single trigger. Sometimes the baseline will be at the correct place, so when this happens I capture the image.

TomC, thanks for helping...

Here it is what you ask.

Thanks a lot for these captures!
They answer some questions I've been wondering about, and pose some new ones!

New question --- The frequency of your 8.4V converter is about 62.6KHz at 230VAC. Compared to the frequency change on mine as the mains voltage was increasing (frequency decreasing as voltage increased), it seems that your PSU stays close to the 65KHz programmed frequency. Why? Is this because of a difference between the R7731N and the R7731A? Is it because my R7731A is flaky? Maybe I can find the answer when I test my old PSU......

Answered question --- The peak voltage at Q1's drain is about 462V. Q1's breakdown voltage is 600V. It seems that the designers allowed a fair safety margin.

A reminder to SDS series users:

The scope's maximum input voltage spec is 400V. While testing voltages in excess of this spec you should insure the probe is set to X10 to protect the scope's input. Also remember that the supplied probes have a maximum rating of 600V. If you need to test anything higher you should use a high voltage probe.

[TomC]

The pin6 is enable pin, Owon just connect with Vin, typical and evaluate schematic set a 1nF decoupling capacitor. I believe that this must adding.

It seems that this IC's output could be delayed via this pin if necessary, Owon didn't use this feature and enables it as soon as Vin is available.

The pin7 & 8 are joined together. From this point Owon puts the D127 to gnd and through the L3 inductor with 3 caps parallel, C36/5uF, C45/12uF and C44/470uF.
This way differs some from evaluate schematic. At the evaluate schematic there is RC parallel to D127 and at the output there are two electr. caps of 22uF. I think that needs 1uF smd parallel to diode. The output needs more investigation with two inductors or pi filters.

The RC is probably a snubber. Perhaps you can scope the waveform at D127's cathode to see if there is excessive ringing. If there is ringing a snubber can help.

[TomC]

at the second there is a 10uH inductor like Owon does by hand.
The result at the second captures is worst and I don't know who from Owon thinking that solution!

It seems like the inductor is forming a resonant circuit with stray capacitance, causing all the extra noise you see on the captured image. Perhaps adding an appropriate capacitor in pi arrangement (as you mention in next post) may stop the ringing and give better noise results.

[lemon]

OK, TomC take your time that you are needing and I am here to measure whatever you want.

I prepare a work about AZ1094 circuit...it has a lot of interesting!

That'll be interesting!

Your PSU board is different from mine, so I attached images of where I think it'll be easiest to hook up the probes. CH1 should be on D8's anode, and CH2 on Q1's drain. Both ground leads to the Z-plate. Make sure the probes are set to X10 because the peak voltage at Q1's drain may be more than 400V with 230VAC mains. While the scope is running you'll see an image like #1, jumping up and down. When the baseline of the CH2 trace is level with the ground marker it is as closely referenced to the Z-plate ground as you can get. To get a capture like #2 I used single trigger. Sometimes the baseline will be at the correct place, so when this happens I capture the image.

TomC, thanks for helping...

Here it is what you ask.

Thanks a lot for these captures!
They answer some questions I've been wondering about, and pose some new ones!

New question --- The frequency of your 8.4V converter is about 62.6KHz at 230VAC. Compared to the frequency change on mine as the mains voltage was increasing (frequency decreasing as voltage increased), it seems that your PSU stays close to the 65KHz programmed frequency. Why? Is this because of a difference between the R7731N and the R7731A? Is it because my R7731A is flaky? Maybe I can find the answer when I test my old PSU......

Answered question --- The peak voltage at Q1's drain is about 462V. Q1's breakdown voltage is 600V. It seems that the designers allowed a fair safety margin.

A reminder to SDS series users:

The scope's maximum input voltage spec is 400V. While testing voltages in excess of this spec you should insure the probe is set to X10 to protect the scope's input. Also remember that the supplied probes have a maximum rating of 600V. If you need to test anything higher you should use a high voltage probe.

There is no any information at the datasheet about differences btw sot-26/dip-8 that explains this different behaviour on frequency (except power dissipation and Package Thermal Resistance).
Unfortunately, I have no any comparing about your schematics and my psu circuit for some difference...
General, the range of frequency operation from 50-130KHz is normal.

About the maximum input voltage. I don't remember well but I think that the maximum of 400V is the adding of ac/dc components of singal and peak to peak not rms or average.

[lemon]

at the second there is a 10uH inductor like Owon does by hand.
The result at the second captures is worst and I don't know who from Owon thinking that solution!

It seems like the inductor is forming a resonant circuit with stray capacitance, causing all the extra noise you see on the captured image. Perhaps adding an appropriate capacitor in pi arrangement (as you mention in next post) may stop the ringing and give better noise results.

Yeap, it wants more search and more knowledge about PSU Noise Filtering.
I am thinking to start from start, i.e from the input and some decoupling 1nF to various pins (according to evaluate schematics) having the output without any filtering (maybe only the electrolytic capacitor) and at the end to apply any changes at the output.

[lemon]

Please, if someone has measured the values of smd capacitors C45, C40, C41 from the adapter board Ver. 3.2 or 3.3 it''ll be very appreciated. They are next to L2 & L3 5R6 inductors.

[TomC]

About the maximum input voltage. I don't remember well but I think that the maximum of 400V is the adding of ac/dc components of singal and peak to peak not rms or average.

You are right!
I'm attaching the actual specs so this will be clear to all members. Don't want to see any more BOOMs!

[TomC]

Please, if someone has measured the values of smd capacitors C45, C40, C41 from the adapter board Ver. 3.2 or 3.3 it''ll be very appreciated. They are next to L2 & L3 5R6 inductors.

Lemon, I tried to measure them, but they have to be unsoldered to get the correct values. So I'll have to be someone that have taken them off for experiments or repairs. The value I got is useless (.63 mF), but all three of them measure this same value in circuit because they are for all practical purposes in parallel.

[Carrington]

Tomorrow I could measure all them by separately. Well, not the most smaller, because I've lost it.

[TomC]

Tomorrow I could measure all them by separately. Well, not the most smaller, because I've lost it.

That would be great! Thanks!

Any news on your EMI shielding project?

[lemon]

Tomorrow I could measure all them by separately. Well, not the most smaller, because I've lost it.

Carrington for version 3.0 I have measured these little smd capacitors next to L2 (I unsoldered all of them), see at a quote of my previous message. I need the values for version 3.2/3.3 if it is possible.
TomC, thanks for the trial but I know there isn't way to measure right on pcb

...
The pin7 & 8 are joined together. From this point Owon puts the D127 to gnd and through the L3 inductor with 3 caps parallel, C36/5uF, C45/12uF and C44/470uF.
...

Really, like as Tomc says, have any result from spray shielding?

[TomC]

Today I wanted to see the signal across the current sense resistors (R5/R5A/R5B/R5C). This signal represents the current flowing through the primary winding when Q1 is turned ON. I spent considerable time trying to get a good capture, but the best I could get was a signal with an upward slant. The problem is again the fact that all primary signals are referenced to GND-A but the scope ground lead has to be on GND-C to avoid a short circuit. In the case of the current sense signal I had to set CH2 to 500mV/Div to get a reasonably viewable signal, but this makes the half wave rectified sine wave where it rides so large that it's impossible to pick a signal from the top of it. So I had to settle for a slanted signal. CH1 is connected to the anode of D8 to provide a reference of the cycle timing. I would have preferred to use Q1's drain for this, but when you connect even a short wire to this element it seems to emit radiation so strong that a low level signals such as the current sense signal is obliterated and replaced with an image of Q1's signal. This effect fooled me for a while but I couldn't believe what the signal was telling me, 11A flowing through Q1. So I kept digging until I realized the signal I was looking at wasn't real. The correct value as shown in the images is less than 1A.

#1 Shows 2 complete cycles of operation.

#2 Shows just the part of the cycle when Q1 is ON and the current is ramping up through the primary winding.

#3 Illustrates the reason why I had to settle for a current sense signal with an upward slant. The capture shows the half wave rectified sine wave with the current sense signal riding on it. The top of the half wave don't fit on the screen because of the CH2 V/Div setting, and as a result the only available current sense signals are on the slope up or down.

[Carrington]

Please, if someone has measured the values of smd capacitors C45, C40, C41 from the adapter board Ver. 3.2 or 3.3 it''ll be very appreciated. They are next to L2 & L3 5R6 inductors.

C45=C41=10uF
C40=100nF

Edit: This cap are from the adapter board Ver. 3.0.


About EMI: I don't know anything of the new boards, Aidetek is not responding to my messages, and my adapter board V3.0 is damaged. So I could not try anything.

[Carrington]

Carrington for version 3.0 I have measured these little smd capacitors next to L2 (I unsoldered all of them), see at a quote of my previous message. I need the values for version 3.2/3.3 if it is possible.

Oh sorry, I misunderstood you. I don't have the adapter board Ver. 3.2 or 3.3. The above values are for the 3.0 Ver.

[TomC]

About EMI: I don't know anything of the new boards, Aidetek is not responding to my messages, and my adapter board V3.0 is damaged. So I could not try anything.

That's a bummer! 
Can your V3.0 board be repaired, or is it a total loss?

[lemon]

Please, if someone has measured the values of smd capacitors C45, C40, C41 from the adapter board Ver. 3.2 or 3.3 it''ll be very appreciated. They are next to L2 & L3 5R6 inductors.

C45=C41=10uF
C40=100nF

Edit: This cap are from the adapter board Ver. 3.0.

...

Carrington, I know that you have the version 3.0 for older your messages.
I would like to remember you that the sequence of capacitors at the output of AOZ1094(Version 3.0) is C36(smd), C45(smd), C44(electrolytic). To me this sequence is 5uF, 12uF, 470uF
The version 3.2 has different sequence like C45(smd), C44(electrolytic), C40(smd),C41(smd).

For the damage to yours adapter, if you need help I can help you to anything smd works on this (I have the appropriate equipment).

[Carrington]

Thank you very much to all.
The damaged part is the AZ1094 and inductor L3, and yes it can be repaired. But I'm waiting to see what happens with Aidetek, I will report to the forum.

[TomC]

Today I looked at the voltages at the output of the feedback loop op-amps and at the COMP input of the R7731A. Since there are no significant load changes, these voltages should be pretty stable, so I measured them with a voltmeter. I also measured the 8.4V raw output because it is used as the bias voltage for the PH2 opto-coupler. The results were as follows:

                 PH2-2            PH2-4              8.4V raw (DC)             8.4Vraw (AC+DC)
                ------------      ------------       ------------------          ----------------------
100VAC      7.192V          1.620V             8.41V                         8.356V

125VAC      7.192V          1.565V             8.41V                         8.356V

140VAC      7.193V          1.535V             8.41V                         8.356V

From the above I noticed that the only significant variations were at PH2-4, which is connected to the COMP input of the R7731A. This voltage controls the duty cycle, the lower the voltage, the lower the duty cycle. This is supposed to happen when the load is light and the output voltage rises. A lower duty cycles delivers less energy and brings the output voltage back to its nominal value. However, the COMP input is supposed to be controlled by the feedback loop op-amps via the opto-coupler. Neither one of the voltages driving the opto-coupler's LED is varying, so the COMP input shouldn't vary either, in theory. Of course, the input AC voltage is varying, and as we know from previous observations, this has caused other surprises, like causing the R7731's osc frequency to vary. So somehow, it seems to be causing this effect too.

Note that it's normal for the duty cycle to vary when the AC input voltage varies, but on current mode PWM controllers like the R7731A, this is accomplished via the effect of the current sense (CS) input. A higher AC input voltage causes more current to flow through the primary, which in turn causes the CS threshold to be reached sooner, and as a result causes Q1 to be turned off sooner.

Hoping that viewing the voltages with a scope rather than just the voltmeter may reveal something that I may have been missing, I decided to capture waveforms for the previously measured voltages. PH2-2 and the 8.4V raw output are on the secondary side and can be easily captured using GND-C as the reference. PH2-2 is a different story because it is on the primary side and is referenced to GND-A. I did try to capture it anyway, but the results are not trustworthy because you again have to use the math function and the signals are low level. So I'm not going to post that capture. The captures for PH2-2 were done using average mode to eliminate some of the random noise from the results, the 8.4V raw output was captured using sample mode. Again, I couldn't see any significant variations that could justify the voltage variations on PH2-4. So why the voltage at PH2-4 varies is still a mystery to me!

[TomC]

Today I captured the flyback converter's output voltages. CH1 was connected to the 8.4V filtered output at J1-2. Ch2 was connected to the cathode of D9 which is used to power the green LED. Captures were taken at different mains voltages and different time division settings as indicated by the names of the attachments. No significant changes were observed as a result of varying the mains voltage.

This is the final set of measurements I had planned to do on the new Owon PSU board. This board is very similar to the previous version board for which I had previously posted a schematic. The latest version of this schematic can be found in the last attachment. The main difference between this schematic and the new PSU board is that Owon added many SMD bypass capacitors to reduce common mode noise. In addition, Owon rearranged and modified some circuit traces for the same purpose. However, all the component names and values are the same. The following are links to all the other posts that contain measurements and captures that I previously posted for this new Owon PSU.

https://www.eevblog.com/forum/testgear/review-of-owon-sds7102/msg281838/#msg281838
https://www.eevblog.com/forum/testgear/review-of-owon-sds7102/msg282227/#msg282227
https://www.eevblog.com/forum/testgear/review-of-owon-sds7102/msg282577/#msg282577
https://www.eevblog.com/forum/testgear/review-of-owon-sds7102/msg283026/#msg283026
https://www.eevblog.com/forum/testgear/review-of-owon-sds7102/msg283664/#msg283664
https://www.eevblog.com/forum/testgear/review-of-owon-sds7102/msg284227/#msg284227
https://www.eevblog.com/forum/testgear/review-of-owon-sds7102/msg284737/#msg284737

My plan is to use these measurements and captures as a reference for comparison purposes. I'm hoping that this will be useful as I look at the equivalent components on my old PSU board. For this next step I will provide independent power and dummy loads for my old PSU so I can have easier access to its components. The final goal is to attempt to discover new ways of reducing common mode noise keeping in mind ease of implementation.

[lemon]

TomC, keep good woriking about psu.
Your works is best and very soon you find new ways for better noise limited.

If you want to make some measurements for you, cause 230Vac, don't hesitate to ask me.

[AndrejaKo]

Hi! I need a simple test of the scope, to see if it's just me or if this thing that's happening to me is normal.

So can anyone please set the scope to X-Y mode, invert one of the channels and report if that makes any difference to what's seen on screen in the X-Y mode? On my scope, it looks like channel inversion isn't working in X-Y mode and is fine in voltage-time mode.

[TomC]

Hi! I need a simple test of the scope, to see if it's just me or if this thing that's happening to me is normal.

So can anyone please set the scope to X-Y mode, invert one of the channels and report if that makes any difference to what's seen on screen in the X-Y mode? On my scope, it looks like channel inversion isn't working in X-Y mode and is fine in voltage-time mode.

Andrejako, I've also had a lot of trouble and disappointment using the X-Y mode. I don't remember if channel inversion was one of them. I'm temporarily away from the lab right now, but I'll test this for you as soon as I get back. In the mean time, here is a link to a previous post where I describe some of the trouble I had with X-Y mode.

https://www.eevblog.com/forum/testgear/review-of-owon-sds7102/msg246541/#msg246541

[TomC]

Hi! I need a simple test of the scope, to see if it's just me or if this thing that's happening to me is normal.

So can anyone please set the scope to X-Y mode, invert one of the channels and report if that makes any difference to what's seen on screen in the X-Y mode? On my scope, it looks like channel inversion isn't working in X-Y mode and is fine in voltage-time mode.

AndrejaKo,

This seems to be another feature that don't work on X-Y mode. The following are some captures while using X-Y mode with my Semiconductor Curve Tracer. They include images for CH1/CH2 Inv OFF/ON.

[AndrejaKo]

Thanks a lot! Too bad that inversion isn't working.

[lemon]

...
There is coming some new, and I think, Owon have also learned something.
-------

Just I saw the manual of Owon TDS Series.
The philosophy and ergonomy of various menus is the same as SDS Series with some impovements and adding some more operations like the capability of touch screen and some others.
They have corrected all the minus of our fw, of course.
I don't know if they think to give us this fw but it'll be a shame if they don't.