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Recent content by danielsoy
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SCR unwanted spurious firing.
Look what I ´ve found about Mosfet´s ringing. http://files.engineering.com/getfile.aspx?folder=7f8dbdbe-0015-4979-b82a-4e5ee52b8cfb&file=avoid_mosfet_ringing.pdf- danielsoy
- Post #26
- Forum: Circuit design
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SCR unwanted spurious firing.
Hi Lionel, thanks for your reply. Those are Msim files. Overshoot is caused, at some point by gate drive from ne555 pwm and because of the lack of snubber across mosfet. That is an issue that I can deal with. IRF is working good now and heating is moderate...- danielsoy
- Post #25
- Forum: Circuit design
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SCR unwanted spurious firing.
Thats right, I may even get a working dimmer for pennies, but the fact is that i want learn something in the way about switching mosfets, scrs and the like. You are very kind to help me, thanx a lot![wavey].- danielsoy
- Post #23
- Forum: Circuit design
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SCR unwanted spurious firing.
Heres a picture of the Drain-Source oscillogram, at 280vdc, tested during a couple of seconds to avoid mosfet overheating. Motor is no loaded, but running free. Would like to know, if rise and fall time are ok, or must be improved. IRF is working without snubber by...- danielsoy
- Post #21
- Forum: Circuit design
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SCR unwanted spurious firing.
A more accurate oscillogram, using another test probe.http://files.engineering.com/getfile.aspx?folder=fde33ac5-a8e3-4831-a70d-c2eb52ba5b64&file=150vdc_18useg_50%..JPG- danielsoy
- Post #20
- Forum: Circuit design
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SCR unwanted spurious firing.
Yes, the thyristor approach was left aside by now, until I find a reliable way to detect zero cross, and be sure that unwanted firing is 100% unlikely. May be, I will try something with a PIC to avoid fake zero cross detections. i like SCR because of its incredible current withstand capability...- danielsoy
- Post #19
- Forum: Circuit design
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SCR unwanted spurious firing.
Sorry, dv/dt is 0.25 volts X nanoseconds.- danielsoy
- Post #17
- Forum: Circuit design
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SCR unwanted spurious firing.
dv/dt is like a cloud thats waiting to rain over me, any time a turn a switch off[tongue] This time is not that bad, because its inside IRF840 SOA. look:http://files.engineering.com/getfile.aspx?folder=421e5727-8ca9-48bc-bb53-dedf1d117225&file=dv_Dt_1.5volts_x_nanosec..gif- danielsoy
- Post #16
- Forum: Circuit design
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SCR unwanted spurious firing.
another approach. http://files.engineering.com/getfile.aspx?folder=1dbbb2ad-d095-4ec4-ad48-35be582706cd&file=PWM_irf840_310vcc_motor_control_v4.0.ms12- danielsoy
- Post #15
- Forum: Circuit design
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SCR unwanted spurious firing.
That is not reassuring at all. Now i am a bit concerned about SCR and Triac erratic temper. An spurious low angle firing, may cause the load to receive a lot of current. Guess will try to control my motor, with a PWM signal driving an IRF840 at 310Vcc! [sadeyes].- danielsoy
- Post #14
- Forum: Circuit design
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SCR unwanted spurious firing.
Talking about things that should not be, look this Triac commutation failure. After a couple of positive half cycles, triac cannot block negative half cycles, So load (DC motor), stops turning and starts oscillating in its place under AC current. (red window)...- danielsoy
- Post #12
- Forum: Circuit design
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SCR unwanted spurious firing.
Working OK with 5 watts snubber resistor. No spurious at all! Thanks again to eng-tips ppl for your help [wink]r!- danielsoy
- Post #11
- Forum: Circuit design
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SCR unwanted spurious firing.
A picture of dV/dt between anode n cathode.http://files.engineering.com/getfile.aspx?folder=6a31eeaa-12f8-4015-80ac-d7c510b83745&file=dV_dt_across_scr..png- danielsoy
- Post #9
- Forum: Circuit design
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SCR unwanted spurious firing.
Eureka ppl![thumbsup2] As ITSMOKED and BRIANE22 already pointed, voltage rising rate across SCR anode-cathode, was re-firing my SCR. Snubber was there, but no really working... 20 ohms resitor (1 watt,sorry), in series with .1uf capacitor, was indeed open because of heat. Will keep testing...- danielsoy
- Post #8
- Forum: Circuit design
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SCR unwanted spurious firing.
BTW, MJE1300, was replaced by a bc548 like transistor, that has more Hfe.- danielsoy
- Post #7
- Forum: Circuit design
