High Voltage Transistors and Creepage Requirements

Thread Starter

tindel

Joined Sep 16, 2012
663
I'm currently working on a product for Pollution Degree 2, Material Group II, at a peak working voltage of 200V (150V, actually, but I want some margin). Therefore, I need a creepage of at least 1.4mm on all of my parts with large voltages across them (per IEC60950). Problem is that most of the 'high voltage' transistors on the market have creepages on the order of 1 or 1.1mm or less.

Here's a good example. MSB92WT1G. Advertised as a 300V SOT-323 transistor. If you follow the recommended footprint, the creepage is 1.0mm. Using this product in my design would violate the requirements. In fact, this part would only be good up to about 100V.

Any ideas here? Only thing I can think of is getting a much large transistor at a much higher cost both in transistor price and board real estate, even though a SOT-323 is perfectly capable of getting the job done. I suppose I could also conformal coat the board. That seems silly to do for three parts out of about 50.
 

Picbuster

Joined Dec 2, 2013
982
I'm currently working on a product for Pollution Degree 2, Material Group II, at a peak working voltage of 200V (150V, actually, but I want some margin). Therefore, I need a creepage of at least 1.4mm on all of my parts with large voltages across them (per IEC60950). Problem is that most of the 'high voltage' transistors on the market have creepages on the order of 1 or 1.1mm or less.

Here's a good example. MSB92WT1G. Advertised as a 300V SOT-323 transistor. If you follow the recommended footprint, the creepage is 1.0mm. Using this product in my design would violate the requirements. In fact, this part would only be good up to about 100V.

Any ideas here? Only thing I can think of is getting a much large transistor at a much higher cost both in transistor price and board real estate, even though a SOT-323 is perfectly capable of getting the job done. I suppose I could also conformal coat the board. That seems silly to do for three parts out of about 50.
the transistor mentioned has a distance of 1 mm approx between Emitter and Collector.
The max voltage between basis and emitter = 5V.
I do not see a problem however coating the PCB is always a good practice to avoid damp and rubbish between conductors.

Picbuster
 

Hymie

Joined Mar 30, 2018
708
Why do you need basic insulation across the transistor?

The semiconductor device (transistor) cannot be considered to provide basic insulation because should the transistor fail short circuit, any safety function provided by the transistor will be defeated.

The product safety standard (60950-1) allows substandard creepage distances on the proviso that with the creepage distance short circuited – does not create a hazard.
 
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