DY294 Supertip To Safely Test Small SMPS Adapters
I always wondered if there was a safer and easy way to test small smps power adapters without having to connect them to the dangerous deadly AC power lines anymore. And with all the analyzing tools in the electronic engineering world if such a tool maybe already existed?
The best tester we know about which already safely can test 3 pin voltage regulators, diodes, capacitors and transistors without even destroying them is the DY294 universal HV tester. The great thing about the DY294 is that it can test components up to their breakdown voltage level before normally an avalanche of electrons would destroy our component making them useless parts.
This breakdown maximum voltage limit is always mentioned in datasheets of transistors, and we can safely examine these with any DY294 tester.
But now anyone with a DY294 tester also can test these small smps adapters very fast and safe!
This article explains how anyone can use the High Voltage output of his DY294 to safely test these small power adapters like for instance any 5V USB charger.
Simply connect the diode bridge AC input pins of your hopefully fixed power adapter under test to the Capacitance Test socket (yellow arrow) of your DY294.
And then switch the function selector knob to the maximum test voltage position of about 1000V (which easily can reach up to about 1600VDC!), or use the max 200V scale and press the TEST button. Or use the C and E transistor HV output pins of your DY294 tester. But always observe the right polarity of the circuit under test preventing blowing up e-caps that immediately will explode when the wrong polarity is connected!
If you keep the TEST button pressed in and at the same time test the output of your (in this case a 5V USB charger) adapter with a Led Light connected to the USB port you will see the Led Light flash at any time the test voltage reached about 165V DC. After the voltage drops fast to a much lower voltage and the Led Light dims (it will very fast discharge the primary HV capacitor of your adapter) , and the process repeats itself after the voltage again reaches about 165V DC, after the 5V Led Light (uses normally about 160 mA in my case) flashed briefly again and so on. As long we press the TEST knob on our DY294 it will charge the primary HV capacitor until the charger activates like it would if it was directly connected to the 230VAC power line.
But if nothing happens you have to switch both Capacitor Test wires, or the E and C wires, to the AC pins of the diode bridge of your adapter, or turn the voltage selector to the opposite 200V or 1000V selection.
But keep in mind that only if you have connected your DY294 output directly to both ~AC diode bridge inputs and chose the wrong polarity at best nothing happens and nothing gets destroyed. If you however connected the HV output of our DY294 to the + and – pins of the diode bridge and chose the wrong polarity it of course immediately will destroy your charger and the primary HV e-cap(s)! So ALWAYS check the right polarity BEFORE pressing the TEST button! To test these power adapters I used a 6V larger current 3A adapter to power my DY294, but probably a 2A adapter will work too.
Above photo showed my Led Light that I used to test my fully repaired small 5V USB charger with mlx02367A PWM controller and 13005 NPN HV transistor on its small pcb.
But instead of the much consuming Led Light as load to the charger output we also can just connect any cheap USB 5V voltage tester dongle. That also will work longer on the energy that was pumped into the primary HV e-cap(s) by our trusted DY294 than the short flashing of the Led Light does.
The above presented small 5V USB charger started when the DY294 reached about 145V DC if the selected max voltage scale was 200V, and it reached about 165V DC if the 1000V scale was selected.
By the way another test I did just now was test the today received new (Aliexpress 0,50 euro/p) 5V 2,5A smps adapter on my DY294. With the 8 dip LY2223 pwm controller chip on it. (as mentioned in my recent article on Jestine’s blog about the 5V 3A adapter repair).
This time the smps LY2223 adapter circuit already started to work when the DY294 reached a voltage of just about 50V DC! It showed a superlit secondary blue led, which also kept glowing after the input voltage already had dropped to zero when the HV primary e-cap was discharged. Next photo shows this Raspberry Pi 5V 3A adapter that was fixed in a previous repair.
See also next photo of the component side of the with this method tested 5V adapter that already works at an input voltage on the AC input pins of about 50V DC.
So the voltage level at which the smps adapter under test activates depends solely on the type of controller used and design of the used circuit. The DY294 just outputs up to the max selected voltage.
To conclude this SUPERTIP I also tested if I could extend the active working time of the 5V smps charger adapters under test. On the first presented adapter with the mlx02367A PWM controller.
I did this by parallel connecting a big discharged! 460V DC 220uF capacitor to the C(ollector) connected on the plus pole of my e-cap and the E(mitter) of the DY294 to the – pole. And connected these wires to the AC pins of the diode bridge and pressed the TEST button on my DY294 to see what happened.
No matter if the the 1000V or the 200V scale is selected, the adapter began always at about 0V until it reached about 165V on the 1000V scale, respectively 145V if the 200V max scale was selected. (unsure if the starting voltage difference is real because the LCD display probably takes some time to show its characters or here the 1000V indeed just reaches that voltage level sooner?).
And charging the capacitor to that level took about 2V per second in time. (so give and take about 70 seconds to reach the voltage at which the smps adapter starts working). My USB 5V voltage tester dongle worked on the charged capacitor for about 30 seconds until the DC input voltage discharged to about 50V and the 5V smps USB charger stopped working.
Pressing the TEST button while the USB 5V charger was working, did not help to keep the voltage at 165V DC or to 145V DC if the 200V scale was selected. But right after the charger stopped below about 50V DC pressing the TEST button started to raise the capacitor voltage on the Charger AC diode bridge input again up to about 145V respectively 165V DC after the process starts all over again. Of course only when the TEST button is pressed.
So although testing these smaller 5V charger smps adapters with an 5V USB voltage tester dongle already worked splendidly without the 460V DC 220uF capacitor added, it is possible to extend the working time of the smps adapter considerably! (about a factor 30! from about 1 second to about 30 seconds activation).
I also tested this Supertip with a special High Voltage Insulation Tester (often also called “Megger”) the AR907A+. This device is not as safe as the DY294 semiconductor tester is, and neither does it the things the DY294 is able to test but it does output a stable max selected voltage of 250V DC, upto a dangerous maximum of 2500V! And it is like the DY294 short circuit protected, but probably kills all semiconductors that it is connected to.
Sadly this not as universal AR907A+ device compared to the great famous DY294 only operates on 6 penlight cells because apparently for safety reasons there is no external adapter option and adding an external power jack therefore could be very dangerous! But for delivering a decent 250V test voltage this device did work like the DY294 did but since the AR907A+ eats batteries it is a bad choice if you already have a universal DY294 Tester that already works on a decent 6V 3A external power adapter and does not need any batteries! Also keep in mind that the DY294 safely starts at 0V, the AR907A+ however probably starts right away at the selected 250V DC! So do not use it to test caps with lower max working voltages! And the only thing that the AR907A+ also does is measure AC voltages up to 600V and it shows the Mega Ohm value of the connected device or circuit under test.
Just after I thought that I had finished this article about small smps adapters testing without the usual dangerous power line connection and the commonly used in series placed Light bulb I found a third option to safely test these adapters!
I decided to give my last bought TV LED Backlight tester also a try. I previously had bought another LED Backlight tester that had less adjustable voltage and current setting options why I bought this second one:
This one (US $38.95 59% OFF|Tkdmr 0 330V Smart ) also worked if the voltage was adjusted high enough!
It worked fabulous and incredibly fast! And if you also set the current tumbleswitch to automatic it tests the smps adapter even faster! The 160 mA Led light flashes on about once every second. Faster than it did with the AR907A+ or the DY294! And it also can test e-caps on max breakdown voltages like the DY294 can. And also a few other options on TV backlight powerboard testing.
And the USB voltage tester dongle now was constantly active! The input voltage is exactly adjustable to the point where the voltage tester dongle just switches off. And can be set at a voltage that it is constantly powering the smps output to the USB voltage dongle tester which is at an inputvoltage of around +140V !
I again also added a HV e-cap, a 390uF 400V type, to see how it would improve testing my smps adapter. To the Led backlight tester red and black output probes.
And this now helped to keep the 160mA Led on the output of the 5V USB charger constantly working!! It worked flawlessly instantly and Incredibly well!! I think this method is a SUPERTIP !!
So this is also a very interesting result in testing these smaller smps units! Depending on what device the engineer/reader of this blog can afford to buy and use, there are now at least 3 given options. Of which the last mentioned Backlight Led tester worked the fastest and the best!
Here a final photo of this Backlight Led tester with the now flawlessly and constantly working 160mA 5V Led light and the to the output of the Backlight tester extra added 390uF 400V HV e-cap.
The model I used probably is best compared to other Led backlight testers because of the extra adjusting options this device has. I know that touching the probes is free of any real danger, although the instruction manual with my previous backlight tester warned the user NOT to touch the HV probes, but I know the backlight tester is also short circuit proof for short periods. The instructions included with my previous tester also warned not to keep the Led/Ledstrip under test too long connected to the probes because the current is raised in steps the longer they are connected. And with my new backlight tester there was no instruction manual included but all information is given online on eBay.
Anyway whatever device you decide to use as small smps adapter tester, know that it works and that especially in case you use the DY294 it is safe for engineer and electronic parts! But using the Led Backlight tester was also safe and surprisingly here also the best small smsp adapter tester!
I’m sure this Super Tip will safe time when fixing small power adapters and maybe even safe lives at the same time! This way you won’t need to place a safety Light bulb in series anymore either!
This way you always safely can test your small smps adapters and chargers without destroying anything as long as always the right polarity is observed! And as long as the primary maximum HV e-caps voltage never is violated!
But whatever you do, always double check your circuit under test because here are High Voltages involved! Because you certainly won’t like getting a shock from a 400V fully charged electrolyte capacitor!
Albert van Bemmelen, Weert, The Netherlands.
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