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we are talking about ruthenium oxide ink printed resistors in the 10s-100s of ohms, unconnected to anything prior to trimming; from what I've heard/read, a series of pulses with progressively increasing energy or packets of tightly spaced pulses are required to do the job.
I've seen some patents on voltage pulse trimming techniques applicable to thick film resistors that are otherwise buried or inaccessible to laser trim, but never a commercially available source of such equipment.
Does anyone know companies making that?
Ok, so I added a ptc thermistor cutoff circuit which stops the pwm controller when things get hot.
Now I'm running again into CS transformer reset woes (as with the earlier pushpull design described earlier, but now i have no way of doing bipolar current sensing)at max duty cycle operation. the...
yes, that's one of the options i am considering. another one could be a thermistor on the buck stage mosfets, comparator and hysteretic over temperature hiccup in the event of short on the output or any other fault. i never actually shorted the output with full the 440V on the 470uF cap there...
I had secondary side snubbing issues with the conventional push-pull causing severe ringing across the bridge rectifier diodes. Thus, i was compelled to go with 1200V devices, which is actually why i picked the current-fed push-pull. There is no secondary side inductor, no ringing and buck stage...
following up on this, I went a different route and changed the topology to cascaded current fed push-pull converter, which automatically solved secondary side rectifier ringing (no inductor there). The controller is LM5041 configured for current mode operation. While it's running nicely, I can't...
Ok, so i swapped out the soft recovery diodes with C4D02120A SiC parts, which somewhat reduced secondary side ringing and overshoot, but it's still there and it needs snubbing for a nice and linear primary side current sensing.
some regenerative snubber suggestions are more than welcome!
I'm going to see if soft recovery diodes (DSEP8-12A) yield any improvement over jellybean 5A 1000V parts, 5cents a pop. 1200V SiC diodes still bear hefty price tags...
With cst location sorted out, I've got to focus on the output snubber now. Without any, there's some serious ringing exceeding 1kV, which blows the €€€€ out of the bridge rectifier, plus it superimposes ripple onto the cst output, rendering the primary side current control rather jerky. Now im...
The burden resistor (after the diode) is 2 ohms. No significant improvement even with 1ohm. The cst has 100 turns.
I need to run the power xfrm at high duty cycles instead of increasing the turns ratio because otherwise the big difference between the average and peak voltage on the secondary...
Hi
I'm building a 12-440V/500W push-pull converter based on the UC2825A pwm controller.
The current sense xfrm (toroid)is now placed over the common junction of the two primaries, thus receiving unipolar pulses. The max duty cycle is ~93% so it has very short time to reset and fails to do so at...
That is exactly what i did ( turn off mosfet, not power) with 2 transistors emulating a thyristor. control voltage is taken from the source shunt. i tested this arrangement with voltages up to 350v and the improvised 'thyristor' turns off the mosfet in less than 500ns of shorting the output. the...
thanks for your input
it seems that the SOA of irfp460 could indeed be violated unless the short circuit condition is removed instantly. for example, in the circuit from the first post Ishort would be 2.5-3A meaning i have a couple of msec to remove it or bring Vgs below Vth.
the intended...
hi
The design intent--switch RL /200-600 ohms of equivalent resistance/ off of 350vdc to gnd with a mosfet acting like a low side switch and provide short circuit protection. the output of the source has total bulk capacitance of 200uF low esr capacitors
Ive added diode clamped series inductors...
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