Author Topic: Lab Power Supply Turn ON and OFF Characteristics  (Read 7410 times)

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Offline mahi

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Re: Lab Power Supply Turn ON and OFF Characteristics
« Reply #25 on: October 06, 2024, 07:10:34 pm »
Rohde & Schwarz HMP4040 (pre-facelift): 4-channel power supply with 32V/10A (up to 160W per channel, 384W total) - datasheet

Measurements with voltage set to 8V, current to 40mA and a resistor of 50 ohm.

Switch on:

#1 HMP4040 CH1 switch on - 1V/div - 50ms/div (*)
#2 HMP4040 CH1 switch on - 1V/div - 5ms/div (*) (**)

(*) I had to take 1V/div instead of 500mV/div because of the overshoot
(**) Due to the duration of the overshoot, it did not make sense to go shorter than 5ms/div, so no 100µs/div screenshot included

In CC mode I'm measuring 39.75mA with a recently calibrated Fluke 289 (average because it actually fluctuates between 39.6 and 39.9mA) while the HMP4040 indicates 39.9 .. 40.1mA.

Peak detect on the Fluke 289 measures 155.9mA at switch-on which is very close to what we can see in the oscilloscope measurements.

(the multimeter was not in-circuit during the oscilloscope measurements)

Switch off:

#3 HMP4040 CH1 switch off - 500mV/div - 50ms/div
#4 HMP4040 CH1 switch off - 500mV/div - 100µs/div

I did not see differences in behavior between the channels, so I've included screenshots of channel 1 only.
« Last Edit: October 11, 2024, 05:11:53 am by mahi »
 
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Offline Furna

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Re: Lab Power Supply Turn ON and OFF Characteristics
« Reply #26 on: October 06, 2024, 08:19:11 pm »
Rohde & Schwarz HMP4040 (pre-facelift): 4-channel power supply with 32V/10A (up to 160W per channel, 384W total) - datasheet
[...]

Looking at the datasheet I realized this PSU has also sense wires; did you try using sense?
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Offline mk_

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Re: Lab Power Supply Turn ON and OFF Characteristics
« Reply #27 on: October 06, 2024, 08:38:24 pm »
Rohde & Schwarz HMP4040 (pre-facelift): 4-channel power supply with 32V/10A (up to 160W per channel, 384W total) - datasheet
[...]

Looking at the datasheet I realized this PSU has also sense wires; did you try using sense?

for CC-testing?
 

Offline sonpul

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Re: Lab Power Supply Turn ON and OFF Characteristics
« Reply #28 on: October 06, 2024, 08:39:18 pm »
RIDEN RD6006P
Siglent SDS1202X-E  50ohm resistor.
 
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Offline Furna

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Re: Lab Power Supply Turn ON and OFF Characteristics
« Reply #29 on: October 06, 2024, 08:53:33 pm »
Rohde & Schwarz HMP4040 (pre-facelift): 4-channel power supply with 32V/10A (up to 160W per channel, 384W total) - datasheet
[...]

Looking at the datasheet I realized this PSU has also sense wires; did you try using sense?

for CC-testing?

In the analog world it doesn't  make any sense I know ... but in digital/software world it might.
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Offline Martin72

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Re: Lab Power Supply Turn ON and OFF Characteristics
« Reply #30 on: October 06, 2024, 09:01:17 pm »
Something else that occurs to me when I see all these pictures:
At work, so-called discharge circuits are tested from time to time.
The principle is simple: if the auxiliary voltage is removed (the device has been switched off), an FET conducts and the electrolytic capacitors in the DC link can discharge quickly via load resistors.
And very quickly at that...
So, now colleagues had the “problem” when testing this board that the discharge curve, which is normally very steep, drops rather “limp”.
What's the problem? At the power supply unit that provides the auxiliary voltage for testing the board.
We have dozens of laboratory power supplies with these “enable” buttons for the outputs.
If you press this to turn it off, the voltage is not immediately gone, but decreases slowly - as some pictures here show.
Do you know what I'm getting at...
It is possible that some power supplies have a capacitance at the output after the switch.
That is why the output voltage is not immediately gone after switching off.


Offline nctnico

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Re: Lab Power Supply Turn ON and OFF Characteristics
« Reply #31 on: October 06, 2024, 11:07:20 pm »
Something else that occurs to me when I see all these pictures:
At work, so-called discharge circuits are tested from time to time.
The principle is simple: if the auxiliary voltage is removed (the device has been switched off), an FET conducts and the electrolytic capacitors in the DC link can discharge quickly via load resistors.
And very quickly at that...
So, now colleagues had the “problem” when testing this board that the discharge curve, which is normally very steep, drops rather “limp”.
What's the problem? At the power supply unit that provides the auxiliary voltage for testing the board.
We have dozens of laboratory power supplies with these “enable” buttons for the outputs.
If you press this to turn it off, the voltage is not immediately gone, but decreases slowly - as some pictures here show.
Do you know what I'm getting at...
It is possible that some power supplies have a capacitance at the output after the switch.
1) The on/off button isn't driving a relay but simply forces the output voltage setting to 0 at the point where the setpoint is fed into the output stage. I have modified quite a few power supplies to add this feature. Simply short the voltage control potmeter to ground to disable the output using a toggle switch. But in a digitally controlled PSU it is a simple matter of having the DAC which drives the output stage output 0V. Same principle though.

2) The rapid discharge effect you are describing is a parallel power sinking circuit (Keysight calls this a downprogrammer https://docs.keysight.com/kkbopen/66xxa-down-programming-589741416.html) which kicks in when the output voltage is higher than then setpoint voltage. So when an output is switched off, this circuit will kick in because the output voltage is higher than the setpoint. But it will also kick in when power is fed into the power supply. Attach a fan and turn the output on / off. Chances are you see the current becoming negative due to the sink circuit absorbing the power from the fan while it is spinning down and working as a generator. However, this feature is not available in all power supplies so you need to check the specs. A way to tell whether a PSU has a sink circuit is when the voltage fall settling times are specified as well.
« Last Edit: October 06, 2024, 11:13:04 pm by nctnico »
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Offline sonpul

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Re: Lab Power Supply Turn ON and OFF Characteristics
« Reply #32 on: October 06, 2024, 11:18:27 pm »
The RD6006P has a 10uF output. When turned off, the output is shunted to ground by the circuit, accelerating the discharge of this capacitor. In my screenshot of the shutdown, you can see the beginning of the discharge first and then a sharp decline.
« Last Edit: October 06, 2024, 11:28:29 pm by sonpul »
 

Online ArdWar

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Re: Lab Power Supply Turn ON and OFF Characteristics
« Reply #33 on: October 07, 2024, 04:09:06 am »
Please note that my resistor load is 45Ω

R&S NGP804
PS001: Turn ON without any slew control. Stays at 8V for approximately 16ms before exponential decay and settle into ~2V. Which means slightly more than 40mA setpoint. I don't have external DMM, but internal readback is 41mA.Scope reading hints even more than that (~44mA)
PS002: Turn ON with 20ms slew setting. Peaked at 7.5V before decay. If you extrapolate out the initial jump, the slew is indeed approx 20ms, into 8V... (i.e. ~400V/s)
PS003: Turn ON with 100ms slew setting. Peaked ar 4.7V before decay. Slew rate is approx 80V/s
PS004: Turn ON with 200ms slew setting. More or less the same behavior. Peaked at 4.2V. Slew rate is indeed ~40V/s. SO far I still can't quite figure out what dictates the peak voltage w.r.t slew settings. It neither stays at constant voltage nor constant time.
PS005: Turn OFF. No drama here. Interesting that the slope is linear instead of exponential.

Keithley 2281S
PS011: Turn ON with max (1000V/s) slew. Peaked all the way at 8V before decay. Slew rate is actually ~600V/s. Settling bang on at 1.80V, 400mA. Verified by DMM6500.
PS012: Turn ON with 100V/s slew setting. Peaked at 3.7V. Slew rate is actually ~107V/s. Just like the R&S, peak points are neither at constant voltage nor time. Also note how it settles into 1.7V for a while before "snapping" into 1.8V
PS013: Turn OFF with max (1000V/s) slew. Nothing weird other than the initial drop by ~100mV for 6.2ms before the distinctly stairstep slew down. Not sure how's the slew rate here, the stairstep section is ~1000V/s.
PS014: Turn OFF with 100V/s slew. Similar behavior as before, only scaled up in time. Slew is indeed approx 100V/s in the linear section.
« Last Edit: October 07, 2024, 07:17:52 am by ArdWar »
 
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Online ArdWar

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Re: Lab Power Supply Turn ON and OFF Characteristics
« Reply #34 on: October 07, 2024, 04:53:58 am »
Like before, load is 45Ω

GWInstek, I think it is PPE-3323 although not really sure.
PS021: Turn ON. (Almost) typical linear PSU behavior. Interesting that CV-CC switchover apparently happen at 200mV. It also sink ~0.5mA when output disabled, not unusual with certain design.
PS022: Turn OFF. Your typical exponential output cap decay. Very slightly accelerated by 0.5mA sink.
Interesting ripple, ~5.6s period :o
2394235-0

Keithley 2461
PS031: Turn ON. Even a SMU have its quirks. Distinct three steps output: initial step into 50mV and stay there for a whooping 125ms, jumps into ~1.3V, before finally jumps into 1.8V. Output is bang on at 40mA.
PS032: Zooming in at the weird bump. Not sure what it is.
PS033: Turn OFF. Clean step, no drama here.
« Last Edit: October 07, 2024, 12:06:48 pm by ArdWar »
 
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Offline mahi

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Re: Lab Power Supply Turn ON and OFF Characteristics
« Reply #35 on: October 07, 2024, 04:57:54 am »
Looking at the datasheet I realized this PSU has also sense wires; did you try using sense?

The sense terminals are always in use. In the HMP4040 they are connected to the output terminals via 1.5 kohm resistors inside the power supply. The only moment it makes sense to run separate sense wires to the DUT, is when losses in the wires are relevant. That is not the case in this test.
 
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Offline 3isenhorn

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Re: Lab Power Supply Turn ON and OFF Characteristics
« Reply #36 on: October 07, 2024, 08:01:33 am »
I love the idea of collecting some data, so here is my share:

1) Keysight E3640A

The control loop ramps up and then goes slowly to the limit. Since this supply has a low and high voltage mode (8V/20V), You see the results for turning on in low mode in Fig. 1 and for high mode in Fig. 2.

2) Agilent E3614A
Although similar in number, this has not a dedicated output  button. When the supply is turned on, the output is on.
When we turn on, as shown in  Fig. 3, we see some ripple below 0.5V in the beginning, due to the mechanical turn-on switch.
However, the control loop has a severe overshoot up to 6V for 116us, as shown in detail in Fig. 4.

3) Korad KD3005P

The supply also has no dedicated outpouring on/off. Which led to a  massive overshoot up to 8V and a small hick-up of around 0.2V in the beginning. As shown in Fig. 5.

Figs. 6, 7, 8 and 9 show the corresponding tune-off behavior, with nothing too special.

Hope this is helpful.
« Last Edit: October 07, 2024, 08:07:18 am by 3isenhorn »
 
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Offline mhsprang

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Re: Lab Power Supply Turn ON and OFF Characteristics
« Reply #37 on: October 07, 2024, 09:06:13 am »
Today I received a reply from Rohde & Schwarz: a UPS label and an RMA form to return the unit.

I replied that I won't be returning my PSU because the problem is not exemplary but a design error. I told them they can take any NGE100 or other model from their inventory and reproduce this problem.

I also included the links to both threads on this forum.

Whenever I hear more from them, I will post it here.
 
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Offline Furna

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Re: Lab Power Supply Turn ON and OFF Characteristics
« Reply #38 on: October 07, 2024, 09:13:26 am »
Looking at the datasheet I realized this PSU has also sense wires; did you try using sense?

The sense terminals are always in use. In the HMP4040 they are connected to the output terminals via 1.5 kohm resistors inside the power supply. The only moment it makes sense to run separate sense wires to the DUT, is when losses in the wires are relevant. That is not the case in this test.

Thank you for your answer; next time I will also read better the datasheet and the manual  :)
Different brand's sense is implemented differently and can be enabled/disabled ...
Now the point is: what is the MCU doing before realizing it is time to lower the voltage?
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Offline mhsprang

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Re: Lab Power Supply Turn ON and OFF Characteristics
« Reply #39 on: October 07, 2024, 11:15:10 am »
Looking at the datasheet I realized this PSU has also sense wires; did you try using sense?

The sense terminals are always in use. In the HMP4040 they are connected to the output terminals via 1.5 kohm resistors inside the power supply. The only moment it makes sense to run separate sense wires to the DUT, is when losses in the wires are relevant. That is not the case in this test.

Thank you for your answer; next time I will also read better the datasheet and the manual  :)
Different brand's sense is implemented differently and can be enabled/disabled ...
Now the point is: what is the MCU doing before realizing it is time to lower the voltage?

Sense wires have no effect in CC mode. The PSU drives a constant current into the load, no matter what the resistance is. Current flowing through a string of resistors is the same in every single resistor. The test leads are resistors in that chain.
 

Offline Furna

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Re: Lab Power Supply Turn ON and OFF Characteristics
« Reply #40 on: October 07, 2024, 11:37:30 am »
Looking at the datasheet I realized this PSU has also sense wires; did you try using sense?

The sense terminals are always in use. In the HMP4040 they are connected to the output terminals via 1.5 kohm resistors inside the power supply. The only moment it makes sense to run separate sense wires to the DUT, is when losses in the wires are relevant. That is not the case in this test.

Thank you for your answer; next time I will also read better the datasheet and the manual  :)
Different brand's sense is implemented differently and can be enabled/disabled ...
Now the point is: what is the MCU doing before realizing it is time to lower the voltage?

Sense wires have no effect in CC mode. The PSU drives a constant current into the load, no matter what the resistance is. Current flowing through a string of resistors is the same in every single resistor. The test leads are resistors in that chain.

All correct but if you enable/disable sense, it might alter how the MCU works i.e. more/less MCU cycles before lowering the voltage.
We are speaking about how fast the PSU switches from CV to CC.
Also different materials have different characteristics; 50Ω of wound wire resistor has different inductance than 50Ω of carbon resistor and that matters during power on and switch from CV to CC.
Real world is different than text books.
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Offline mhsprang

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Re: Lab Power Supply Turn ON and OFF Characteristics
« Reply #41 on: October 07, 2024, 11:56:01 am »
All correct but if you enable/disable sense, it might alter how the MCU works i.e. more/less MCU cycles before lowering the voltage.
We are speaking about how fast the PSU switches from CV to CC.
Also different materials have different characteristics; 50Ω of wound wire resistor has different inductance than 50Ω of carbon resistor and that matters during power on and switch from CV to CC.
Real world is different than text books.

First of all, as a user of a power supply I would like to not be bothered with figuring out how my PSU behaves. I want to read that in the specifications. Second: I sincerely hope that no manufacturer in their right mind would implement the sense system in software! After all, the entire sense-circuit is no more than making the feedback point of the feedback loop available on terminals. Oh crap... that feedback loop!

This brings me back to an earlier statement I made: I think the entire feedback loop of a PSU should not be in software at all unless you have DSP-like capabilities and 100+ kHz ADC/DAC sampling rates.

Just take a beefy power op-amp and use that as a voltage follower after a DAC and there's your digitally controlled, 4 quadrant PSU. How hard can that be? Add a current mirror driven by a second DAC, controlling the output current in CC mode. I remember the application note of the venerable LM12 was full of examples.

And at last, you can add an ADC to actually read back the set values under load.
 

Offline Furna

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Re: Lab Power Supply Turn ON and OFF Characteristics
« Reply #42 on: October 07, 2024, 12:12:17 pm »
All correct but if you enable/disable sense, it might alter how the MCU works i.e. more/less MCU cycles before lowering the voltage.
We are speaking about how fast the PSU switches from CV to CC.
Also different materials have different characteristics; 50Ω of wound wire resistor has different inductance than 50Ω of carbon resistor and that matters during power on and switch from CV to CC.
Real world is different than text books.

First of all, as a user of a power supply I would like to not be bothered with figuring out how my PSU behaves. I want to read that in the specifications. Second: I sincerely hope that no manufacturer in their right mind would implement the sense system in software! After all, the entire sense-circuit is no more than making the feedback point of the feedback loop available on terminals. Oh crap... that feedback loop!

This brings me back to an earlier statement I made: I think the entire feedback loop of a PSU should not be in software at all unless you have DSP-like capabilities and 100+ kHz ADC/DAC sampling rates.

Just take a beefy power op-amp and use that as a voltage follower after a DAC and there's your digitally controlled, 4 quadrant PSU. How hard can that be? Add a current mirror driven by a second DAC, controlling the output current in CC mode. I remember the application note of the venerable LM12 was full of examples.

And at last, you can add an ADC to actually read back the set values under load.

We are going off-topic; this thread is exactly: "How does your PSU behaves when you put it in a crazy condition at Power ON? Take a mesasure with your oscilloscope."
Also I didn't say I want sense systems in software.
I said that taking a measure with sense on/sense off (in case the PSU allows as Siglent SPD4000x series) takes 5 minutes and removes the doubt  8)
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Offline pdenisowski

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Re: Lab Power Supply Turn ON and OFF Characteristics
« Reply #43 on: October 07, 2024, 02:29:19 pm »
Today I received a reply from Rohde & Schwarz: a UPS label and an RMA form to return the unit.

I replied that I won't be returning my PSU because the problem is not exemplary but a design error. I told them they can take any NGE100 or other model from their inventory and reproduce this problem.

I also included the links to both threads on this forum.

Whenever I hear more from them, I will post it here.

We are still actively investigating this issue, and I've been in direct communication with the product manager and our technical expert since you made your first post about this last week. I had already sent them these threads for reference as well.  I also just PM'ed you my email address so that you can reach our to me directly.

Although many of our product managers and R&D engineers do read EEVblog and watch YouTube, contacting us directly would likely be a much more efficient form of communication.  I can assure you that we take this (and all other) customer issues seriously, so please feel free to email me directly if you have any concerns or questions.
« Last Edit: October 07, 2024, 02:33:07 pm by pdenisowski »
Test and Measurement Fundamentals video series on the Rohde & Schwarz YouTube channel:  https://www.youtube.com/playlist?list=PLKxVoO5jUTlvsVtDcqrVn0ybqBVlLj2z8
 
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Offline mawyattTopic starter

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Re: Lab Power Supply Turn ON and OFF Characteristics
« Reply #44 on: October 07, 2024, 02:57:02 pm »
With the new Siglent SPD4000 series we find it interesting that the results from CH1 and CH2 are different wrt to the conditions discussed here as shown by Furna. We don't see this with the older SPD3303X as both channels behave the same as expected!! Also, haven't seen any post that indicate other supplies have different behavior with 2 main channels with same specs as one would "expect" the detailed design and implementation of the channels would be identical. 

Would be interesting to find out why, as this is quite puzzling?

Best
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Offline Furna

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Re: Lab Power Supply Turn ON and OFF Characteristics
« Reply #45 on: October 07, 2024, 04:57:00 pm »
With the new Siglent SPD4000 series we find it interesting that the results from CH1 and CH2 are different wrt to the conditions discussed here as shown by Furna. We don't see this with the older SPD3303X as both channels behave the same as expected!! Also, haven't seen any post that indicate other supplies have different behavior with 2 main channels with same specs as one would "expect" the detailed design and implementation of the channels would be identical. 

Would be interesting to find out why, as this is quite puzzling?

Best

For whom is not following the Siglent SPD4000 series thread, my measurements of Siglent SPD4121X are available at
https://www.eevblog.com/forum/testgear/new-siglent-spd4000x-series-power-supply/msg5667709/#msg5667709
https://www.eevblog.com/forum/testgear/new-siglent-spd4000x-series-power-supply/msg5667823/#msg5667823

Siglent SPD4000 series has 4 channels that are inerhently different ...
SPD4121X in particular has
CH1-CH4 15V 1.5A are independent
CH2-CH3 12V 10A can be setup in series/parallel and both also have 4wire sense
« Last Edit: October 07, 2024, 05:50:58 pm by Furna »
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Online Antonio90

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Re: Lab Power Supply Turn ON and OFF Characteristics
« Reply #46 on: October 07, 2024, 06:13:18 pm »
A few measurements from the GPD-4303S and the Yokogawa 7651 DC source.

Please note, all measurements done with standard 10X probes, and 8v 40mA, except channel 4 from the GPD, which only goes to 5.2V.
Resistor measured at around 54.17 Ohms.

Edit: The math trace is the current at 20mA/div (i think it is pink?)
« Last Edit: October 07, 2024, 06:20:14 pm by Antonio90 »
 
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Offline _Wim_

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Re: Lab Power Supply Turn ON and OFF Characteristics
« Reply #47 on: October 07, 2024, 07:11:03 pm »
A few of the power supplies I own (for the fast ones, I also added a 2ms timebase). Test with 50ohm resistor / 8V / 40mA. Interesting is the GS200, which can work in current mode and voltage mode.
 
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Offline Martin72

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Re: Lab Power Supply Turn ON and OFF Characteristics
« Reply #48 on: October 07, 2024, 09:10:58 pm »
1) The on/off button isn't driving a relay but simply forces the output voltage setting to 0 at the point where the setpoint is fed into the output stage. I have modified quite a few power supplies to add this feature. Simply short the voltage control potmeter to ground to disable the output using a toggle switch. But in a digitally controlled PSU it is a simple matter of having the DAC which drives the output stage output 0V. Same principle though.

2) The rapid discharge effect you are describing is a parallel power sinking circuit (Keysight calls this a downprogrammer https://docs.keysight.com/kkbopen/66xxa-down-programming-589741416.html) which kicks in when the output voltage is higher than then setpoint voltage. So when an output is switched off, this circuit will kick in because the output voltage is higher than the setpoint. But it will also kick in when power is fed into the power supply. Attach a fan and turn the output on / off. Chances are you see the current becoming negative due to the sink circuit absorbing the power from the fan while it is spinning down and working as a generator. However, this feature is not available in all power supplies so you need to check the specs. A way to tell whether a PSU has a sink circuit is when the voltage fall settling times are specified as well.

Regarding 2):
I may have expressed myself a little misleadingly (or the translator).
I actually wanted to explain how most of the off-state images here come about, using a practical test example on an assembly.
Be that as it may, I may get around to adding a few pictures of this this week, but of Peaktech power supplies... ;)

Offline mawyattTopic starter

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Re: Lab Power Supply Turn ON and OFF Characteristics
« Reply #49 on: October 07, 2024, 09:23:37 pm »
With the new Siglent SPD4000 series we find it interesting that the results from CH1 and CH2 are different wrt to the conditions discussed here as shown by Furna. We don't see this with the older SPD3303X as both channels behave the same as expected!! Also, haven't seen any post that indicate other supplies have different behavior with 2 main channels with same specs as one would "expect" the detailed design and implementation of the channels would be identical. 

Would be interesting to find out why, as this is quite puzzling?

Best

For whom is not following the Siglent SPD4000 series thread, my measurements of Siglent SPD4121X are available at
https://www.eevblog.com/forum/testgear/new-siglent-spd4000x-series-power-supply/msg5667709/#msg5667709
https://www.eevblog.com/forum/testgear/new-siglent-spd4000x-series-power-supply/msg5667823/#msg5667823

Siglent SPD4000 series has 4 channels that are inerhently different ...
SPD4121X in particular has
CH1-CH4 15V 1.5A are independent
CH2-CH3 12V 10A can be setup in series/parallel and both also have 4wire sense

That's unusual that CH1 and CH4 are the same and CH2 and CH3 are the same but different from CH1 and CH4, this explains the difference since CH1 (15V 1.5A) is not the same specification as CH2 (12V 10A) and thus one might expect a different response from such!!

Now looking at the Siglent page for the SPD4121X shown, this arrangement looks OK with terminals for CH1 logically on left then the channels proceed to right as 2 thru 4 (not like GPP 4323 where Instek placed CH4 on left, then 2 thru 4 1 thru 3 towards right  :o

The 4000 display shows 1 to 2 top and 3 to 4 below left to right which makes sense, however because of the arrangement the similar channels are diagonal not left to right as one would expect!!

Imagine using a typical analog supply arrangement of +-15V (or +-12V), then the important display channel parameters (V and I) are diagonal not left to right for the active channels. So glancing at the active channels in this common use case requires determining the individual channel parameters on diagonals rather than side by side!!

This makes no sense IMO, would like to hear the logic behind this arrangement from Siglent designers!!!

https://siglentna.com/power-supplies/spd4000x-series-programmable-linear-dc-power-supply/

Best,
« Last Edit: October 08, 2024, 12:02:17 am by mawyatt »
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