Today I am at the lab, testing a small SMPS (power supply) for LED applications. A quick search on the web revealed a company in Poland as the manufacturer of this PSU. I was quite interested to check the performance and to compare it with the advertised specifications. Although this PSU is made in China (a lot of things are made there nowdays 🙂 it may be designed in Poland. Correct me if you have more information about it.
The first test was to monitor the output voltage when the PSU is powered from the mains. I used a digital storage oscilloscope (Tek TDS2022B) to capture the moment the PSU is powered on. The output rise time was 11.2ms without load, and 14.9ms with 100% load. Very good figures well within spec. The specifications indicate 30ms maximum rise time measured for a 0% to 90% of rated output at full load. I went for 0-100%. So, no complaints here. Below is the screenshot from the instrument for the 0% load measurement.
At this time, the setup time was also measured. The setup time is the time it takes for the output voltage to stabilise at the desired output, when a significant load is applied. To do the test, I applied a step load of 3A and measured a setup time of about 50ms. Not bad at all. What alerted me though was the excessive amount of high frequency noise in the output. See below for more information.
Next, the output voltage setting potentiometer was tested. According to the specification , the output can be adjusted between 11.5V and 13V dc. The measurement was made with my trusty Fluke 87V. The accuracy of this multimeter for DC voltage measurements is (+-0.05% +1). The adjustment range of the PSU was found to be 11.16V to 13.09V and so, within spec.
Next the output voltage ripple at 12VDC was measured for three situations. Without load, with 50% load and with 100% load. The rated output current is 3A so this was taken as 100% load, and 1.5A was drawn for the 50% load test.
The specification has a special note regarding the output ripple. It says:
“Ripple & noise are measured at 20MHz of bandwidth by using a 12” twisted pair-wire terminated with a 0.1μF i 47μF parallel capacitor “
My setup was a twisted pair of wires, terminated with 100uF 25V capacitor, and the channel of the oscilloscope limited to 20MHz bandwith. The image below shows the pair of wires used. The probe is connected directly on the capacitor legs and the other side of the wires to the PSU output terminals.
The measurements are presented in the table below. A programmable electronic DC load (BK Precision 8601) was used to perform the tests.
|0% load Ripple||50% load. Ripple||100% load. Ripple mV|
|340mV pk-pk||476mV pk-pk||548mV|
The output ripple is not within spec. My setup may have not been in favor of the test since I used an ordinary electrolytic 100uF capacitor and probably with higher ESR than necessary. In any case, this is the total ripple containg all the high frequency components allowed within the 20MHz bandwidth. The noise was superimposed on the ripple and was not periodical so a statistical (with display persistance of 5sec) measurement was made with the cursors. The screenshot below shows the 100% load situation
The following test was to put the protection modes of the PSU under the microscope 🙂 . The specification indicates a current overload on the range of 105-150% of rated current. The protection method offered is hiccup mode with auto recovery when the overload is removed.
I gradually increased the load and the hiccup protection mode kicked in at 3.9A. That is 130% of rated load. Power supply behaved nicely by shutting down the output and testing for overload condition every 420ms. The measurement is shown below.
Finally, the short circuit protection was tested. Without load, the PSU output was shorted. The output voltage rised normally (within spec) once the short was removed. The test was performed twice. No complaints at all.
Before giving my opinion on this product, I run it with 100% load for 10 minutes and the temperature rise was found ~30C (degrees of Celsius).
My impression for this little SMPS is that it is a low cost well performing power supply, with adequate protection against abuse… I would not be very paranoid about the high frequency content of the output (since the average ripple is within spec), given the targeted applications. Further fitlering would be absolutelly necessary though for an audio application but that is to be expected anyway for a switching supply.
I am happy with it, lets use it in a project…