TNY280 in buck topology
Hi Although the TNY280 is intended for flybacks, I try to use it in buck topology due to cost reduction (and LNK306 is not available in my area). The trial circuitry is attached. I’ve got a 16V at output, but I noted the TNY is heating as much as Vin rises. At 300VDC the case temperature is definitely above 65C and may be much more. Also I’ve attached a signal on the S pin of the TNY. May be it’ll be useful. I’ve tried other inductors up to 4.7 mH. No results. What can I do wrong? Thank you, Alex
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Hi! V_BP is 5.8 V. I’ve re-checked myself. The heating was even at 100VDC input voltage. Some improvement occurred when I was placing a 0.47-1 nF cap between EN and S pins. Before pulses followed as bursts with some intervals (“TNY280_source.png”) Now they follow continuously, and no oscillations are between them (pls look at the attached “TNY280_source_pin_Cap_on_EN.png”). There is no heating at 100 VDC, but it is at higher voltages. Yes, I think about switching losses too. But where they came from? Inductor’s parasitic capacitance? I use a SL1016 inductor from Yageo - http://www.yageo.ru/pdf/SL.pdf Alex
Hi,
The switching losses is due to Coss (Drain to source capactiance of the Power MOS). Due you have TNY274 or TNY275 device you can try? TNY274 has small Coss compared to TNY280 and switching loss should be lower at high line.
rgds..
Yes, I've tried a TNY274, but it cannot power a 0.3A load.
It might be worthwhile to try TNY279 and 278. They are available for me. I'll do it ASAP.
Both TNY279 and TNY278 have heated like the previous part.
I've assembled a flyback with the same parts.
TNYs work fine and are slightly warm.
The transformer is warmer than the TNY.
But PCB area and cost are very large in comparison with the buck converter.
The use of LNK306 is an only solution, isn't it?
Hi,
I think LNK306 is the Lowest cost and component count buck converter solution.
Hi,
Can you please check the voltage on BP pin? The fact that temperature is rising with Vin is suggesting that switching losses is higher at higher Vin.
rgds..