CTG-60W-12V power supply, a pretty good one

I actually reviewed an entire series of these power supplies, but this particular one got held up in transit somehow, so I’m only publishing its test results now. And believe me, this SMPS is worth showing you.

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For those who forgot or didn’t see it, this is the review I’m talking about: this review. It might come in handy. I may add this review to the previous one later.

The construction is the same as the previous models: a light-colored, flat, ventilated case, nothing unusual. But I want to point out that, generally speaking, the lower the rated power of a power supply to begin with, the better it handles overloads. Naturally, I’m talking about models in the same product line, not just any models, though this applies to those to some extent as well.




The assembly is neat, and the board is coated with protective varnish, which isn’t all that common, though it should be. Even ordinary Plastik-70 improves reliability and protects against dust.


The connections are standard: a pair of terminal blocks, a three-pin one for mains and a four-pin one for the load, although with such a low current, two pins would have been enough.


1. The input has a filter, a fuse and a thermistor. The only thing missing, perhaps, is a varistor—and that’s a shame. The unit can be disassembled, so it’s repairable.
2. Aishi 47 µF, 400 V input capacitor.
3. The hot side of the power supply. The PWM controller is also coated with varnish, but there’s probably nothing particularly special here.
4. A group of current-sense shunt resistors and an Sif5N64 high-voltage transistor, rated for 5 A and 650 V—more than enough for this power level.



1. The transformer is flat; this is a Slim-class power supply, after all, and it’s assembled very neatly.
2. The output section. The board is clearly single-sided, so all the components are visible. You can also see the Y capacitor at the bottom.
3. A 20 A, 100 V diode. Obviously, it would overheat at 20 A, but the point is that there should be at least a threefold safety margin, and this one has that covered.
4. There’s an inductor at the output to reduce ripple, along with four 1000 µF, 16 V capacitors. And I have to say, four capacitors is really the right way to do it. I might replace one with a polymer capacitor, but it’s fine as is. Of course, 25 V capacitors would be preferable, but to be fair, 16 V ones will work just fine in this setup, precisely because they have plenty of capacitance headroom and the surge currents are shared across several capacitors.




There’s an insulator under the board, plus a pair of thermal pads under the transistor and diode assembly, which is also the right way to do it.


The measured input capacitance is about 43 µF, and the output capacitance is 4562 µF. That’s perfectly fine for the rated current of 5 A and 230 V mains. I especially like the output capacitance. But for 115–120 V mains, the input capacitance may be too low, so I recommend reducing the power by about 20–25%.



For the tests, I used my usual EBC-A10H, mostly because it can plot handy graphs and has a decent automatic test function.



The protection trips at about 7–7.1 A with the power supply cold and about 6.9–7 A when hot. That’s a bit high, in principle, but it depends on the temperatures recorded during the load test.




I didn’t measure this model’s efficiency initially. In fact, ever since I burned out my favorite wattmeter, I haven’t been measuring efficiency on power supplies rated below 100 W. Unfortunately, trying to measure anything with a wattmeter whose readings jump around between, say, 153.5 and 155.2 W is... difficult. Plus, it’s painfully slow.

But I got an Atorch wattmeter just today. I wouldn’t call it a proper measuring instrument, but since these devices usually use energy-metering chips, its readings should be trustworthy enough. Plus, it handles low currents (and power levels) more accurately, which is what I need.
So I used a different, more convenient electronic load in this case and measured the efficiency.


I measured efficiency over the 0.5–7.0 A range, and I have to say that the fairly flat graph suggests it measures more accurately.
I got about 84%, which is typical for a flyback converter of this power.


The ripple is also fine. Here are the results with no load and at currents of 2, 4, and 6 A.
Even at 6 A, which is effectively a 120% load, the total peak-to-peak ripple, including the spikes, was 100 mV. The main component, which is what essentially reaches the load, was only about 30 mV.


At low frequencies, you can see the “green mode” in action. Ripple at 100 Hz is almost nonexistent—in fact, it’s negligible.



As usual, the test was run in intervals of about 20 minutes at load currents of 2, 4, and 6 A. I noticed a slight positive voltage drift with temperature (about 10–20 mV), while the voltage was practically unaffected by the load.



Results at load currents of 4 and 6 A; there’s no point showing them at lower currents.

At 4 A, everything stays relatively cool. At 6 A—which, as I mentioned, is effectively an overload—the results are more interesting.
The transformer is at 80°C, which is great; the high-voltage transistor is at 82°C, also no problem. The output diode assembly is around 100°C. That may be a bit high, but considering the power supply was running under overload and still has at least 10–15°C of headroom, it’s perfectly acceptable.




Conclusion.
In my opinion, this is a good example of a quality power supply. I might lower the overload protection threshold a little. Otherwise, the build quality is good, the components are fine, it handles a 120% load with ease, has relatively low ripple, and maintains good output voltage stability. I think it’s definitely worth recommending.

That’s all for now. I hope you found this useful. As always, I’d be glad to hear your comments, and thanks to Vitaly for providing the sample for testing.