Help with SMPS current sensing

[Danko]

Hello!


What do you think about this current sensing?

The green circle is arout 10 piece of SMD resistor. Each one is 1ohm/1206 size.
This is a part is a 500-700W half bridge SMPS. currently, there's no PFC before it, but i'm planning making one...

[Pierre]

Sorry, Danko, but your figure doesn't show correct.
Could you post it again?

Best regards,
Pierre

[Danko]

Originally posted by Pierre
Sorry, Danko, but your figure doesn't show correct.
Could you post it again?

Best regards,
Pierre

I uploaded the picture to my server: http://sziget.mine.nu/~danko/aramkor...nt_sensing.jpg
Maybe, this time this is OK

--
Danko

[Pierre]

The picture is cut below the current sense resistors. I thought you were trying to show us how the current limiting is done, not only the sense resistors. Your arrangement is just how I was proposing: source of the low side mosfet to GND. But, what are you doing with that signal?

Pierre

[Danko]

Oh, sorry. I thought there was some kind of technical problem with the picture.

Here's the current limiting part of my schematic, but ths is now only a schematic, ha couldn't test the circuit, becouse of my exams. I'm an Electrical Engineer student...
I know, there should be one or more capacitors near R8 R33. This/theese capacitor(s) will be determined by experiments.

here's the schematic: http://sziget.mine.nu/~danko/aramkor...t_sensing2.jpg
I turned off the part's values, becouse with the values, the picture would be very caotic...
(I have removed the previous pic from my server, becouse that's also uploaded to the forum)

[Pierre]

I am glad you are also using a IR2110/3. My design is also based on it. If everything works ok, perhaps I will move to a gate driver transformer, although that's more expensive.
Have you done any test on the supply so far? Does it work well (apart from the current limiting)?

About the current limit, what is the control chip number? If we don't know that, we will not be able to help you.

Best regards,
Pierre

[Danko]

Originally posted by Pierre
I am glad you are also using a IR2110/3. My design is also based on it. If everything works ok, perhaps I will move to a gate driver transformer, although that's more expensive.
Have you done any test on the supply so far? Does it work well (apart from the current limiting)?

About the current limit, what is the control chip number? If we don't know that, we will not be able to help you.

Best regards,
Pierre

I dealt a lot with the voltage-stabilizing. The feedback always oscillated. Finally, I hope i made it OK. Now the feedback (voltage) is made with a TL431, and an optocoupler. the previous version worked with "wired-in" Z-diode, and optocoupler.
About the gate-driver-transformer. I dont like it, becouse it is hard (or just harder) to find, than an IC.
But, to tell the truth, it is almost inpossible to destroy a gate driver transformer. I have killet about 10 IR2113 ...

In this version of my SMPS I use TL494, as PWM-controller, but i'm planning to use Onsemi's MC<I-dont-know-the-exact-number> Resonant Mode PWM Controller, to reduce switching loss, and to reduce EMI.

[Pierre]

I wish you best of luck with your design.

What do you mean with "Wired Z-diode"?
Did you succeed in putting it to work without feedback (always at maximum duty cycle) first? What power level did you reach?

Best regards,
Pierre

[Danko]

Originally posted by Pierre
I wish you best of luck with your design.

What do you mean with "Wired Z-diode"?
Did you succeed in putting it to work without feedback (always at maximum duty cycle) first? What power level did you reach?

Best regards,
Pierre

Thanks for the wishes

I mean under "wired z-diode", that i soldered the diode, and a few resistors to the PCB with wires. At that stage, I was testing a few stabilizating methods.

Without feedback, it worked good, but /as I counted on it/ the output voltage dropped a lot, when I put a big dummyload on the SMPS.
As far as I remember, the highest output power, I measured is about 600-650watts. The efficiency (this was the goal of that measurement) was about 90-93%.
I thought, that was a little bit too much for the switching devices (IRF740), so I haven't loaded the SMPS such bit load, since that time. I have a few APT5015BVR MOSFETS (500V/32A :-D ), with them, the SMPS can deliver more power. But there's a limitation of the half bridge topology. I think, using half-bridge for more than 900-1000watts is not economic enough. For such output power, the full bridge is better. I think.

Bye: Danko

[N-Channel]

Danko-

I think you are referring to several chips from OnSemi.

1) The PWM chip is the MC33025. This is essentially the next-
generation SG3525 with the follwing goodies added: Wide-
bandwidth error amp, high-current totem-pole outputs (+/-2A),
Higher-frequency oscillator (2MHz), and either voltage- or
current-mode operation. Pin-out is similar to the '3525, but
there are a few differences. (See the datasheets at OnSemi's
website.)

2) the Resonant-mode chips are:
a) MC33066 Resonant-mode controller
b) MC33067 Zero-switching Resonant-mode controller.

The difference between the '33066 and the '33067 is that the '33067 achieves either true zero-voltage, or zero-current switching depending on what method of control you'like to have.

I have used the MC33025 in both DC-DC and Off-line converters, both hi- and low-power, and report good results with it. AND, it works well with the MPIC2113 (OnSemi's obsoleted version of the IR2113). I have not, as yet, tackled the variable-frequency control methods like resonant and quasi-resonant. Too much math there. UGH! Anywho, If you can get the extended-temp range PWM chip (33025) you will find you get pretty good results with it.

BTW, 90-93% efficiency for a 600-700W converter is VERY good. you must be very good in your overall design to achieve that figure the first time!

Post more pics.

Steve