DPA422 short circuit protection

Hi,

Please find following my respsonse to your quesiton:

1. There are many names for these products; Aluminum clad, aluminum base, Metal clad(MCPCB), Insulated Metal Substrate(IMS or IMPCB), Thermally conductive PCBs, etc… but they all mean the same thing. A thin layer of thermally conductive but electrically insulating dielectric is laminated between a metal base and a copper foil. The copper foil is etched into the desired circuit pattern and the metal base draws heat away from this circuit through the thin dielectric. If you want to check what exactly is this material, you can contact the PCB providers, they should be able to give you addtional informaiton.

2. The DPA has integrated feature for over load protection, so with a proper design, the power supply will enter into auto restart mode under output short circuit fault condition. Would you please provide more detail informaitoin about the short circuit test that causes the explosion of the part?

Tery,

Yesterday, I already reply your inquire. But maybe my replying was not going throught. May you answer my question or call me at 510-657-4444 Ext 124

My answer to your questions is

When the power supply run full load, I started increase the load, the DAP422 went to pop out.

Also, when the power supply run full load, I shorted the output two terminals, the DPA422 went to pop out.

Thanks,

Johnson  

Thanks,

Johnson Pi 

Hi,

Thanks for sharing the information. To find the reason of the failure, here are things that I propose you to check:

1. Would you please monitor the drain voltage and drain current under full load condition / maximum input voltage? I want to check how much margin you get in your design and check if the transformer went to satuation or not.

2. Would you attach your schematic and PI-expert design that I can have a check with you?

Thanks 

Power Integration or Terry,

Last week, I sent the PI simulation result and schematic about my appplication but since that, I haven't got any respond ot your comment about my design. Do you need more time?

Thank you very much!

Johnson Pi 

Power Integration or Terry,

Last week, I sent the PI simulation result and schematic about my appplication but since that, I haven't got any respond ot your comment about my design. Do you need more time?

Thank you very much!

Johnson

Power Integration or Terry,

Last week, I sent the PI simulation result and schematic about my appplication but since that, I haven't got any respond ot your comment about my design. Do you need more time?

Thank you very much!

Johnson

Hi, Johnson:

This morning I got an email forwarded from one of my colleage with the schemaitc, transformer spec and the pi expert design files, thanks for providing this informaton. Would you please attach these files in the post instead of sending emails in the future, it will take very long time till I get them as I do not know who is the person that you sent to. Sorry about it.

I did check the schematic, I did not find anything obvious wrong. You may choose the voltage rating for the VR1 to be 100V instead of 91V. But I still can not figure out what casued the blow up of the device during the output short circuit fault by checking the schmatic only.

Would you please check following items:

1. Please record the drain voltage and current with input voltage equal to 75Vdc and full load.

2. When you did the output short circuit, what is the input voltage level during the test. Would you please check if you use 16Vdc as input voltage, and make a short circuit to the output, what will happen?

3. In stead of short the output voltage, would you please increase the output load from full load 1A slowly to 2A, see what will happen. And if the power supply goes into auto restart, it will be interesting to see the drain voltage during the over load fault conditon. 

Please attach the results in the post if you get them, I can further assitant you on that.

Thanks 

Hi! Terry,

Thanks for your feedback about PI simulation.

I will test the circuit for your question 1 and 3. tomorrow.

For question 2, When I did the output short ciruict, the input voltage is 28V.

Thanks,

J Pi 

Hi! Terry,

Thanks for your feedback about PI simulation.

I will test the circuit for your question 1 and 3. tomorrow.

For question 2, When I did the output short ciruict, the input voltage is 28V.

Thanks,

J Pi 

Hi! Terry,

Please see attached osociscope waveforms regarding to the drain voltage.

1. when input voltage is 28.5V, with normal load, 0.2A, the drain voltage (peak) is  130V.

2. When input voltage is 28.5V, with over load , 0.4A, the drain voltage (peak) is  170V.

3. When the input voltage is over 36.5V with 0.4A load, the drain voltage (peak) is 240V.

After I increased the input voltage over 36.5V, (during load is 0.4A), the power supply will be turned off without any damage. Then after the voltage come back low than 35V, the power supply output come back.

Let me know your mind.

Thank you very much!

J Pi 

Hi, Johnson:

From the waveforms that you attached, It is clear that the blow up during the output short circuit is caused by the over voltage break down of the MOSFET.

As what have been  proposed, please check the polirity of the VR1 and make sure the correct component is used. 

Let's keep discussion after your checking in case you have addiontal questions.

Thanks 

Dear Terry,

I have checked VR1 polarities and R1 and R2 resistor's resistance and found they are all right. But I found the problem for the drain voltage transient spike going to high is because the snuber resistor value was wrong. It posts to be 18 Ohm but my technician put only 5 Ohm ( two 10 ohm in parellel) and then I put 20 ohm (two 10 ohm in seris. Then the transient spike become clear. The maximum pike of drain voltage only 64V (it is not vaiable with the load changes).

Also I found the output inductor's inductance can be satuated when output load current going higher. Then I used two 3.3uH, 355mA inductor in parallel, and then the output is much stable.

However, when the two terminals of output is shorted, the DPA422 is still being poped up. I checked the rest connection and didn't find any significant error yet. We need further continue taking effort on it.

Thanks,

J Pi 

Hi, Johnson:

Frankly speaking tt is still not so clear for me why the drain spike voltage changed completely with adjusting the snubber resistor value on the secondary diode. Do you have the drain voltage waveforms recorded after you made this resistor adjustment? I would also recommand you to check all the components on the board, to make sure they are the same as what are shown in the schematic.

To check what caused the blow up of the IC, would you please record the drain voltage with the highest input voltage, full load and over load (1.5times o 2 times of the full load current). We can check if there is enough margin for the MOSFET drain voltage or not.

Sorry. See attached.

Hi,

Are these waveforms drain voltage? Do you know what is the reason of having negative voltage during the turn on period? It looks like this is the voltage on the transformer bias winding or secondary winding, would you please help to confirm?

And would you please also include the test condition when you record the waveforms, for example, input voltage, load current...ect. ?

Thanks 

Please disregard the waveforms I sent and they was recorded by the AC signal in oscillascope setting.

The issue has been located. This topic can be turned over.

Please disregard the waveforms I sent and they was recorded by the AC signal in oscillascope setting.

The issue has been located. This topic can be turned over.