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Power supply for home lab - do I really need a R&S?

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thm_w:

--- Quote from: nctnico on October 02, 2024, 08:27:40 pm ---I think the control loop is in software though. I have an Agilent 66311B which has the same 'problem' (delayed current limit). If the current limit is done in an analog circuit, then I don't see how you can screw up a power supply circuit that bad. OTOH, it could be done to deal with circuits which have a rush-in current which otherwise wouldn't start up properly. Some DC-DC converter modules are prone to not starting when the current limit is set too low. But I can't see this as a good point on a general purpose lab PSU though.

--- End quote ---

With the 66311B "Mobile Communications DC Source" you could make the argument its not a general purpose PSU, so there will be trade-offs to optimize it for high speed response. I would argue a general purpose PSU should prioritize safety and stability over speed.

Here is an old R&S DC source PSU (ngmo), same issue but much faster response:

mhsprang:

--- Quote from: rf-messkopf on October 03, 2024, 05:18:53 pm ---
--- Quote from: mawyatt on October 03, 2024, 12:28:36 am ---That's totally unacceptable behavior from any supply, it's a disaster in the waiting for just about any sensitive electronics use we can think of.

--- End quote ---

I don't disagree with that statement but this behavior is quite common for a number of supplies from reputable manufacturers.

I just tested the supplies I currently have on the bench. All set to 8 V, 10 mA, loaded with 50 ohms. The attached pictures show the output voltage when the load is connected to the supply.

HMP4040-E3646A.png: green trace: R&S HMP4040, white trace: Agilent E3646A.
6632B.png: Agilent 6632B, with rear panel "Fast/Normal Operation" switch set to "normal" (notice the time scaling).

The Agilent 6632B hangs at 8 V for about 150 ms.

--- End quote ---
If the output is enabled before you connect the load, you will obviously see a spike due to the capacitor on the output of the PSU. The idea is that you connect the load first, then enable the output. That is what I have been doing. And in that case, I think no overshoot should be tolerated.

rf-messkopf:

--- Quote from: mhsprang on October 03, 2024, 06:44:05 pm ---If the output is enabled before you connect the load, you will obviously see a spike due to the capacitor on the output of the PSU. The idea is that you connect the load first, then enable the output. That is what I have been doing. And in that case, I think no overshoot should be tolerated.

--- End quote ---

Okay, I thought you are after the transition from voltage to current regulation. Attached see the test with the output being switched on (green trace: HMP4040, white trace: Agilent E3646A), load is 50 ohms again.

mhsprang:
Here are the results from the power supplies I have at home. The Delta is a pure analog supply, the TTi is at least digitally controlled, has a keyboard and all, but I don't know of the control loop is analog or digital. The Tenma is also digitally controlled but cheap: €99. Setup is 8V, 10 mA in 50 Ohm. Load connected, then outputs enabled. Two screen shots each with different time bases, to see short term spikes and "long term" stabilisation of the set current.

mawyatt:

--- Quote from: mhsprang on October 03, 2024, 06:44:05 pm ---
--- Quote from: rf-messkopf on October 03, 2024, 05:18:53 pm ---
--- Quote from: mawyatt on October 03, 2024, 12:28:36 am ---That's totally unacceptable behavior from any supply, it's a disaster in the waiting for just about any sensitive electronics use we can think of.

--- End quote ---

I don't disagree with that statement but this behavior is quite common for a number of supplies from reputable manufacturers.

I just tested the supplies I currently have on the bench. All set to 8 V, 10 mA, loaded with 50 ohms. The attached pictures show the output voltage when the load is connected to the supply.

HMP4040-E3646A.png: green trace: R&S HMP4040, white trace: Agilent E3646A.
6632B.png: Agilent 6632B, with rear panel "Fast/Normal Operation" switch set to "normal" (notice the time scaling).

The Agilent 6632B hangs at 8 V for about 150 ms.

--- End quote ---
If the output is enabled before you connect the load, you will obviously see a spike due to the capacitor on the output of the PSU. The idea is that you connect the load first, then enable the output. That is what I have been doing. And in that case, I think no overshoot should be tolerated.

--- End quote ---

That's what we've shown (with Blue LED as load), and agree on acceptable overshoot!!

Best

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