I have a question about TOP271EG 's spec.

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Hello. My name is Seong Rak Choi.

There are questions about using the product(TOP271EG).

I can not speak English very well and I appreciate your understanding.


In TOP271EG's datasheet, drain pin peak voltage is -0.3V ~ 725V(23page).

But in our product using the TOP271EG, drain pin voltage is -15V ~ 510V. ( I guess -15V is due to counter-electromotive force.)

So I'm worried about the problem. I have reviewed the datasheet again, but it does not detail the minimum voltage.

What I am wondering is how the voltage below the minimum voltage will affect TOP271EG.

I look forward to your help and I attach a photograph of the waveform.

안녕하세요. 저는 최성락이라고 합니다.

TOP271EG를 이용해 전원보드를 개발 중에 있습니다.

드레인 핀의 허용 전압은 데이터시트 상으로 -0.3V부터 725V까지로,

해당 IC를 이용해 개발 중인 전원보드에서 드레인 핀을 찍으면 -15V에서 510V가 찍힙니다.

트랜스의 역기전력 때문인 것으로 추정이 되며, 이렇게 최소 전압을 넘어서는 -15V가 어떠한 영향을 주는지 궁금합니다.

데이터시트 상에 최대전압을 넘는 것에 대한 내용은 있으나, 최소 전압에 대한 내용이 많이 기재되어 있지 않습니다.

voltage.JPG106.73 KB

Hi Mr. Choi

on the primary side of Top 271, it is a MOSFET there. So the minimum drain voltage is limit by the body diode of the MOSFET.

-0.3V should be the absolute rating for the body diode voltage rating. Any voltage higher than 0.3V would has a risk to damage the body diode.

The measurement you have for -15V might not be accurate. The probe you are using is a high voltage probe and its accuracy for voltage <20V would not be very tight. And i recommend you use short wire to connect the Top switch Drain and Source pin directly to avoid any trace drop in the power trace.

Best Regards

Dear Sir,
We Have developed a DC -DC converter using DPA426 PI Switch and specification details are given below .

Input voltage range : 16.5V to 72V
Output voltage :15V
Load : 0.5A
The power supply regulation is staring 16.5V when we are connecting to test bench but the source to power supply length is long that resistance should be around 112 Ohms at that time the regulation starting 25V (near the power supply).
Source is 60V and the load is 0.3A. We have experimented the regulation startup is varying by changing the series resistance .

Please suggest a solution for such type of source to power supply far distance .

Hello Giri,

Could you create a new forum for this topic? we want to keep each forum question separately in order to avoid unnecessary confusions.

Best Regards

Hello Woodiskingser,

I could not understand your problem. Would you please create a new forum for your problem. We will support you.

Best Regards

how to simply calculate VOR of TOP switch HX series

Hi Sourabh Tokikar,

You can access the PIXls for transformer parameters (VOR) at the PI Exper Online site. Here is the link https://piexpertonline.power.com/pixls/design/index


Dear Pi

I have a design which is exported from Pi Exper online, Below are specs

Pi device : TinySwitch -4 (TNY285DG)
output voltage = 5v
output current = 1 A
used shield winding
constant voltage output
used post pi filter and snubber circuits

the above-designed transformer gets a heating issue.
heat is mainly generated in input filter capacitors and transformer

i have used the same specs which are generated in the pi expert.

how to reduce the heating issue? and we didn't measure the heat.
how and which parts are needed to measure?

here I have attached the design file, looking forward to seeing the answer

Hi heyitsmekarthi,

You might want to increase the heatsinking on that area. Try increasing the PCB trace thickness.