TNY280G Blows up somtimes at applying mains
Hello PowerIntegrations,
First of all let me introduce myself; I’m a electronic designer in a factory of emergency lighting. We have used the TNY264 and TNY267 for a few years now, without major problems.
For this new project we need a little more power and we would like to use the TNY280, and also the transformer we used with the TNY267. The transformer is a Pulse transformer designed for output 5V 2.4A + 2.4V 0.4A , primary wdg 98 secundary wdg 4 +2 . prim induc. = 1.6mH Lleak = 57µH cap= 136pF. Windings 98/4/2
Now here’s my problem: one prototype has been working for weeks now, but while testing on an other prototype sometimes TNY280 blows when power is swiched on . sometimes after the 4th time somtimes after 4000 on-off cycles. The peak drain voltage is 660Volt and because i find it close to the 700V limit , I designed a new transformer for output 7.2V 2.3A + 3V 0.4A , primary wdg 79 secundary wdg 6 +3 . measured values prim induc. = 900µH Lleak = 336µH (due to manual winding) cap= 127pF. With this the drainvoltage dropped to 525V, but still somtimes the TNY280 blows up at powering on. The clamp circuit I used is 1nF an 86 Kohm resistor (not with zener clamp, this is running hot).
I include the schematic diagram with component valuse i used. Also a picture of the drainvoltage and current and the calculation sheet.
Hope you can help me or give a hint.
Best regards
Eddy
Comments
Hello PI-Tucker ok, I agree, but as you can see in my post I've made a new design and transformer for the TNY280 wich only has a flyback of 525V , and still sometimes at applying mains the TNY blows.??? how kan it be measured if a transformer goes into saturation ?
thanks
Eddy
Can you capture the Vds and Id at startup?
Hi PI-Tucker ,
I included the waveforms at the top of the topic, startup_total.JPG (total until normal operation),startup zoom1 and zoom2, each time the beginning is magnified. Something extra we want to do (not included in the diagram) is starting up and shutting down the TNY @ by means of shorting the BP-capacitor with a transistor wich is activated at by a external circuit @180V, this has been working in previous designs with the TNY267. But with or without this the TNY sometimes Blows up at powering on.
I understand it is very difficult not having the pcb for measuring, but anything you want to know i'll measure.
thank you.
Eddy
I don't see anything particularly bad in the waveforms you sent. However the waveforms didn't capture the maximum Drain voltage.
Do the blowups happen at maximum Vin?
What is the maximum peak Drain voltage during startup at max Vin?
Try doing a slow sweep (~1 mS per div), with the oscilloscope set to max data points, and set to "peak detect".
A transformer designed for the TN267, when used with the TNY280, will saturate and cause extremely high peak Drain currents and possibly very high voltage on the Drain. YOu need to examine the Drain voltage and current at startup to see this.
You need to use the transformer design recommended by PI.