What is the reason to restart the VIPER38HD chip continuously?

[YBoth.1]

Hi, STMicroelectronics teams,

We are working on a project that uses a lot of STMicroelectronics components like VIPER38HD so we used “eDesignSuite - Design, Circuit, and Simulation Tools�? from STMicroelectronics.

The input of our circuit is

IC

VIPER38HD

Topology

ISOLATED FLYBACK

Input

90 Vac - 265 Vac

Output 1

12 V (2 %) - 9.6 W

Output 2

12 V (2 %) - 2.4 W

Recommended design from “eDesignSuite - Design, Circuit and Simulation Tools�?

fig [1]

And as you see in the above fig [1] the used converter is VIPER38HD, and we ordered it with the other components according to the schematic given in fig [1]. After we ordered all components, we made the circuit using VIPER38HD but our circuit did not work and we did not receive desired output voltage wave for the drain pin. After checking Vdd Pin We got to know the chip is restarting continuously. So we check the feed bak pin signal and the control pin signal and their voltages. but they are in between the given range. So we could not understand what could be the reason for the viper38hd chip restart problem. We double-check the component and values but there is no error with that. We checked for short circuits and confirmed that there is no short circuit problem also.

 

We got the above wave for Vdd Pin And Vdrain pin.

We are looking forward to your helping to troubleshoot this circuit and make it work as expected as soon as possible.

Thank you.

[Marco FICHERA]

Hi @YBoth.1​ ,

When reaching VDDon value, the VIPER should be turned on and switch continuously (or, in case of output overload/short circuit, for 50msec at least before being shut down).

From the VDD & VDRAIN figure it seems there are irregular switching intervals with smaller duration, not in line with what expected from VIPER operation.

Q:

• Can we have a magnification of one of these switching intervals with adequate time scales to see bot its total duration and some DRAIN switching cycles?
• How many samples behave like that?

If only one: did you try to replace the VIPER?

If any sample: did you check that there is no interruption in some PCB tracks? Or to disconnect the auxiliary winding and supply the VDD from external, through a DC source?

Regards

Marco

[YBoth.1]

Thank you for your immediate response. The information you provided will help us to move forward and my apologies for the delayed response. 

Yes, I have tried it with three samples of viper38hd but the result didn't change. Yes, I checked that there is an interruption in PCB tracks but there haven't such interruptions. Here I have attached all waveforms which were observed by supplying AC input of 100V through Variac. According to waveforms I can see the feedback voltage is greater than 3V but at that time the maximum output voltage of the +12V side is 8.7V (only at the restarting time of Vdd.). Do you have any ideas or suggestions regarding this problem? We are looking forward to your helping to troubleshoot our circuit as expected as soon as possible.

The waveform of Vdd and V drain [1]

 

The waveform of Vdd and V drain [2]

 

The waveform of Vdd and V drain [3] (Zoomed)

 

The waveform of Vfb and Vcont

 

The waveform of Vfb and Vept

 

Thank you.

[Marco FICHERA]

Hi @YBoth.1​  (Community Member)​ ,

The CONT pin reaches 3V, which triggers the OVP protection.

Please check the dimensioning of the CONT pin voltage divider with respect to the selected auxiliary-to-secondary turn ratio of the transformer.

The issue should disappear increasing ROVP value.

Regards

Marco