12V 10A CCTV camera system power supply pulsating

[rddube]

Re: 12V 10A CCTV camera system power supply pulsating

Specifications: Fluke 87V Industrial Multimeter
Frequency Maximum frequency 200 kHz
Accuracy ±(0.005% + 1)
Maximum resolution 0.01 Hz

[CapLeaker]

Re: 12V 10A CCTV camera system power supply pulsating

Hmm my 179 only goes to 100khz and my 289 to 400khz. Try measuring at the PWM

[petehall347]

Re: 12V 10A CCTV camera system power supply pulsating

think i may have cracked it .. between pins 5 and 6 is a 000 ohm resistor the reported voltages and resistance to ground are different so suspect that resistor ..

[R_J]

Re: 12V 10A CCTV camera system power supply pulsating

R5 does not connect to pin 5, it connects the modfet source to the Sense pin6

[petehall347]

Re: 12V 10A CCTV camera system power supply pulsating

R5 does not connect to pin 5, it connects the mosfet source to the Sense pin6

damn .. moment of madness and poor vision .

[rddube]

Re: 12V 10A CCTV camera system power supply pulsating

Ok, so what do you gentlement think I should try next?

[petehall347]

Re: 12V 10A CCTV camera system power supply pulsating

install transformer and measure frequency at pin 8 .

[rddube]

Re: 12V 10A CCTV camera system power supply pulsating

install transformer and measure frequency at pin 8 .

Ok, checked and it oscillates between 98 hz to 100.5 hz, that is hz, not khz.

[CapLeaker]

Re: 12V 10A CCTV camera system power supply pulsating

That PWM isn’t powering up fully and it’s for some reason stuck in UVLO. I still think there is something wrong in the primary. So yes… your not getting full switching frequency nor full modulation of the frequency.

[harp]

Re: 12V 10A CCTV camera system power supply pulsating

Try put 100k on pin4 rather then 27k... according to datasheet Operating RI Range is 50-250k... a graph show some different conclusion... but 27k is pushing ic to limit.

BTW what is power compsumption of psu?

[rddube]

Re: 12V 10A CCTV camera system power supply pulsating

Try put 100k on pin4 rather then 27k... according to datasheet Operating RI Range is 50-250k... a graph show some different conclusion... but 27k is pushing ic to limit.

BTW what is power compsumption of psu?

Ok, will try that and let you know. Not sure how to measure power consumption of the psu, it is plugged into a 120V outlet?

[petehall347]

Re: 12V 10A CCTV camera system power supply pulsating

Ok, checked and it oscillates between 98 hz to 100.5 hz, that is hz, not khz.

did you have a load connected to dc output ?

[rddube]

Re: 12V 10A CCTV camera system power supply pulsating

did you have a load connected to dc output ?

Yes a 12V fan

[harp]

Re: 12V 10A CCTV camera system power supply pulsating

Just put AC ampermeter in series with one cord, be sure to set it in 10A range.

[momaka]

Re: 12V 10A CCTV camera system power supply pulsating

Lotas you're right, Momaka gave me an idea and I pulled 2 other transformers from scap boards with pretty much the same winding configuration on the primary side, and both show the exact same results. So in the end, I think my transformer is good, the problem is elsewhere, but where??

Maybe.

OK, did the donor transformer have the EXACT same primary and secondary side configuration in terms of windings, or not? This is actually really important.

The other thing that is really important when swapping transformers between PSUs is that the pins have to be matched exactly. For example, for the main winding on the primary side, one leg is always connected to the (+) positive bus on the primary cap (so +170V DC for locales with 115/120V AC mains and +340V DC for locales with 230/240V AC mains.) The other leg on the primary side main winding is always tied to the Drain of the MOSFET (or for PSUs with PWM-FET combo, to the Drain pins.) Likewise, the auxiliary winding on the primary side has two pins, and one should connect to primary side ground (negative lead of primary cap) while the other goes to a diode and a cap (SMD resistor R7 and diode D2 for your PSU). On the secondary side, obviously the output winding ground pin should be tied to ground and positive output tied to the anode of the rectifier. If any of these pins are reversed, the test won't work. So make sure to wire your donor transformer correctly. Like I mentioned, you can do that with jumper wires and the transformer floating above the PCB. Here's an example:
https://www.badcaps.net/forum/attach...1&d=1608943994

Now, if you did all of that above and the results are still the same, you can also do the reverse - that is, try the transformer from the power adapter from this thread into the adapter where you got the donor transformer from. If the donor power adapter ever worked correctly, your transformer should work OK in it too.

And as always when testing these, I suggest using the series incandescent bulb, just in case. At least IME, most flyback topologies are not too picky about the transformers. I've even used the 5VSB output from an ATX PSU to drive another transformer to test it out.

*EDIT*
Also a very good idea to follow up on Harp's suggestion in post #190 above.
According to the OB2268/OB2269 datasheet, if you look at the graph of "Frequency vs. RI", you'll notice the usable range is between 50 KHz and about 240 KHz. This gives RI values of 130 KOhms maximum and 27 KOhms minimum. Since R9 in your PSU = 27 KOhms, then the switching frequency should be around 240 KHz... which is WAY TOO HIGH for most flyback topologies. Try 50 KOhms instead, and if not, increase to 100 KOhms. With 100 KOhms, F_osc should be around 65 KHz, which is a lot more inline with what I would expect out of a flyback PSU.

[rddube]

Re: 12V 10A CCTV camera system power supply pulsating

Ok, so I tried with a 56K resistor and then a 100K resistor and same result, keeps jumping around from 3-6V on the output when there is no load and with a load, nothing.

I didn't do the test of the power consumption, I'm a little afraid of playing with 120V detached bare wires and DMM probes. Unless you think strongly about this, I'd rather skip this test.

What next?

[rddube]

Re: 12V 10A CCTV camera system power supply pulsating

Maybe.

OK, did the donor transformer have the EXACT same primary and secondary side configuration in terms of windings, or not? This is actually really important.

To the best of my knowledge yes they had the same configuration, but if you want I can post some photos if you would like to see?

[momaka]

Re: 12V 10A CCTV camera system power supply pulsating

To the best of my knowledge yes they had the same configuration, but if you want I can post some photos if you would like to see?

If it's not too much of a hassle, then yes - pictures of the donor PSU top and bottom side should be enough to identify.

Also, try the test with the transformer from this PSU in the donor PSU's PCB and see if it produces output.

Ok, so I tried with a 56K resistor and then a 100K resistor and same result, keeps jumping around from 3-6V on the output when there is no load and with a load, nothing.

Keep a 100-Ohm resistor as a load. The no-load results are somewhat meaningless... though if there is some output, even if bouncing, at least it shows the transformer(s) should be working to some extent and the issue could be elsewhere. But verify with the above suggested test and then we can be a little more sure.

I didn't do the test of the power consumption, I'm a little afraid of playing with 120V detached bare wires and DMM probes. Unless you think strongly about this, I'd rather skip this test.

If you have alligator clips and hook up things securely before plugging into power, it's a little less unsafe (hint: this is where it helps to have some heavy paperweights to put on "flying" wires and clips so that even if you catch/pull onto something by accident, you're less likely to get a wire unclipped and cause trouble.)

[rddube]

Re: 12V 10A CCTV camera system power supply pulsating

If it's not too much of a hassle, then yes - pictures of the donor PSU top and bottom side should be enough to identify.

Also, try the test with the transformer from this PSU in the donor PSU's PCB and see if it produces output.

Ok Momaka, will send the photos shortly. Cannot test this transformer in the donor board as they are scrap boards that I have accumulated over the years. Photos to follow.

[petehall347]

Re: 12V 10A CCTV camera system power supply pulsating

as far as i understand changing that resistor should change the frequency somewhat ..i might be wrong though as often i am .