TinySwitch-III or similar Family

More information you can find ont his site:
http://www.powerint.com/en/community/papers-circuit-ideas-puzzlers/circuit-ideas/-high-voltage-input-switching-power-supply-usi

If you need to buy small quantities custom transformers for prototypes, simply fill inquiry form:
http://www.feryster.pl/polski/pytania.php?lang=en

Best regards

Hi CM,

The only limitation on the input voltage for a TinySwitch design is the maximum voltage rating of the power MOSFET inside the device. Most of our devices, (including all in the TNY-III family) include a 700 V power MOSFET. For better field reliability, and to account for component tolerances, we suggest you limit the maximum voltage on the MOSFET to 650 V at all times. During the off-time of the MOSFET, the voltage seen across it will be equal to your maximum input voltage + the VOR of your transformer + the brief turn-off spike caused by leakage inductance of your transformer. The turn-off spike can be significantly dampened by using a clamp circuit across the primary winding. The VOR can also be adjusted with the design of your transformer. Before finalizing your design, be sure to confirm the maximum voltage seen across the MOSFET with your final prototype.

For an example circuit in a similar power range, I suggest examining DI-177 which is listed at: http://www.powerint.com/en/design-support/reference-designs/design-examples

I would also highly recommend downloading our PI Expert design software, which will generate your transformer design documentation for you as well as suggest values for key circuit components.

We do offer a Rapid Transformer Sampling Service (details here: http://www.powerint.com/en/design-support/rapid-transformer-samples) for a marginal fee. Otherwise, transformer vendors are often willing to provide prototype samples for free if you can guarantee minimum production quantities. Please see our list of recommended transformer vendors here: http://www.powerint.com/en/design-support/component-suppliers

Cheers!

Hi PI,
thanks for the information. I looked at the design software which raises a few questions: The Transformers are very bespoke/costly for small projects (100 off)
I was wondering about working backwards from a production transformer which is readily available or something close would be better? (less choice in UK)
also, the question on EMI - radiated and component level around the whole power unit/transformer. Would a cage be a good encloser? The circuit that this would power has some Khz PWM outputs, these may have induced noise/interference. How are these best delt with?
Thanks CM.

Hi,

It is possible to work backwards from a pre-made transformer when designing using the PI Expert software. First, work up an initial design and record the optimized results that the software presents. (Air Gap Length, Primary Inductance, Number of Turns, Wire Gauge etc.) Once you have these results, I would recommend contacting a transformer vendor and asking if they have something similar which they make in bulk. If so, you can manipulate the results in PI Expert to match those actually used in the transformer available to see if this will work in your design. If the software doesn't generate any warnings, you should be off and running. Note that this approach will not give you the most optimized design, and you may find that your efficiency and EMI results are lower than preferable.

Regarding EMI shielding, it's best to address EMI issues by eliminating their source. Noise can be minimized by reducing switching current loop areas, using decoupling components where necessary and damping the voltage at switching nodes with clamp and snubber circuits. Please see our application notes and datasheets for recommendations on how to use layout techniques and decoupling components to minimize conducted EMI in your design. If you find too much noise is being generated by your switching loads, consider adding a ferrite bead on the output cable at the end that's closest to the switching load.