What does "dynamic load" do in a power supply? - Page 1
Forum section: electronics / testgear

author: piranha32
author_rank: Unknown
timestamp: May 18, 2017, 12:32:54 am
content: Hi,while servicing my bench power supply I noticed a jumper switching on and off a dynamic load. Why something like this is present in a power supply? Does it mean that it can also sink current? The power supply is Tenma 72-2010, which seems to be rebadged GW Instek GPS-3030. The default position was OFF.

author: amspire
author_rank: Super Contributor
timestamp: May 18, 2017, 01:09:17 am
content: I can make a guess. It could be related to the speed of the feedback loop. In Dynamic Mode "Off" position, the supply may react to changes in load slowly, but have no overshoot or ringing. In "On" mode, it may react quicker but may have some overshoot or ringing.If you have a digital scope, put it on the output on, say 10V, and switch in and significant load. Perhaps a 10 ohm power resistor. See if the waveforms on connect and disconnect of the resistor are different. Use the scope's second channel to use the resistor voltage as the trigger.A second thing it might be doing is adding that C1211 across the output in non-Dynamic mode.A bigger capacitor on the output means the supply can handle transient current spikes from the load much better, but the output voltage will be slower to change, and the current limit will not include the energy in that capacitor. So say you set the current limit to 10mA and short the output. Initially you will get a spike of many amps from the capacitor as it discharges. With Dynamic mode "On", there would still be a capacitor on the output but a much smaller one, so the energy in the current spike will be much smaller.Edit:My last guess is that it with Dynamic mode off, it adds C1211 to ground on the voltage reference input. This means that if you send a command to change the voltage from say 1V to 10V, the voltage will change slowly in non-Dynamic mode. The G3033 has a linkable 4.7uF 50V capacitor on the voltage reference input. In manual use. you probably would not notice any difference, but with a scope, you would see a definite slope in the voltage change in non-dynamic mode.

author: edavid
author_rank: Super Contributor
timestamp: May 18, 2017, 01:31:11 am
content: The GW Instek GPS series manual says: "For application in audio production lines. the continuous or dynamic load internal selectable." Very helpfulLooking at the circuit, it does seem to speed up the voltage feedback loop.It doesn't change the output capacitance, or provide a current sinking capability.

author: amspire
author_rank: Super Contributor
timestamp: May 18, 2017, 01:37:33 am
content: Quote from: edavid on May 18, 2017, 01:31:11 amWhatever it is, it is probably a mode for automatic testing. If you are using the supply in a production line for automatic testing, you often want the supply to change voltage as quickly as possible. In manual mode, it doesn't matter if the supply takes 100mS to settle.

author: piranha32
author_rank: Unknown
timestamp: May 18, 2017, 02:51:24 am
content: Quote from: edavid on May 18, 2017, 01:31:11 amYou were very close. Switching dynamic load to "ON" makes the transitions between CC and CV modes much slower. Probably "load" refers not to the power supply itself, but to what is connected to it. With dynamic load turned on, the protection circuit seems to be much more forgiving, allowing for short periods over-current condition. Attached are screenshots from my experiments. The PS was loaded with two resistors connected in series, with nominal values 1 and 2 ohms, plus connecting wires. Voltage was set to 10V, and current limited to 3A.Response times with dynamic load switched ON are in the range of 10s to 100s of ms, while with DL switched OFF, the response times are in the range of 100s of us to single ms.CH1 (yellow) is the voltage on the output, CH4 (blue) is the voltage on the negative side of the connection between resistors.The last 2 screenshots show responses to manual simulation of transient overload. With DL turned on, the supply did not even try to switch to CC mode. After turning DL off, it responded immediately.

author: piranha32
author_rank: Unknown
timestamp: May 18, 2017, 03:43:49 am
content: Something went wrong with upload of one of the pulse responses and the same graph has been uploaded for both cases.So here we go: transient responses, take two.

author: piranha32
author_rank: Unknown
timestamp: May 18, 2017, 05:09:11 am
content: Quote from: amspire on May 18, 2017, 01:09:17 amWhere did you find the schematic? I tried to dig in google before posting here, but the best I could find was user manual

author: amspire
author_rank: Super Contributor
timestamp: May 18, 2017, 05:40:02 am
content: http://www.eltest.hu/pdf/GPD3303SM.pdf

author: piranha32
author_rank: Unknown
timestamp: May 18, 2017, 06:20:09 am
content: Thanks for the link, unfortunately they don't have manual for gps3030But still pretty useful repo of manuals.

author: macboy
author_rank: Super Contributor
timestamp: May 18, 2017, 01:09:09 pm
content: You've basically figured it out. It slows the current control loop, allowing for momentary over current (1.7x nominal) while keeping theaverageat below the set current limit. This can be useful when powering audio amplifiers since the load they present is very dynamic and might demand a higher current only very briefly at the peaks of the audio waveform. This is a highly cloned/re-branded power supply design, and this feature is explained better in some manuals than in others.

author: macboy
author_rank: Super Contributor
timestamp: May 18, 2017, 01:17:40 pm
content: If you need to GPC-3030 schematics, I have them.