[neonixie-l] Re: how to protect a MOSFET
I forgot to draw the led resistor... > > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to neonixie-l+unsubscr...@googlegroups.com. To post to this group, send an email to neonixie-l@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/419a0687-4e79-4f8f-b18a-38ed43d28180%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[neonixie-l] Re: how to protect a MOSFET
Is there a particular reason for using a MOSFET in this application rather than a jellybean NPN transistor? Small signal MOSFETs are fragile things anyway, and exposing them to the set up you have with separate boards just seems like an inherently troublesome approach. Jon. -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to neonixie-l+unsubscr...@googlegroups.com. To post to this group, send an email to neonixie-l@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/8973b651-7248-4f69-8889-54ad2347fd60%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[neonixie-l] Re: how to protect a MOSFET
I used these MOSFETs because I found them in several schematics dimming RGB LEDs using PWM. I’m trying now with a BC548 with a 4.7K resistor between the base and the pwm controller pin. It works great. So, bye bye 2n7000, welcome BC548 :-) Thanks a lot for your input! > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to neonixie-l+unsubscr...@googlegroups.com. To post to this group, send an email to neonixie-l@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/74828da7-ce1b-48f8-8114-675984e19ab6%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[neonixie-l] Re: Nixie, CRT, indicators for sale
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[neonixie-l] Re: how to protect a MOSFET
I've used many MOSFETS in my clocks, with zero problems. In my opinion, the main nixie-ish advantage of a MOS device versus bipolar ( NPN or PNP) is that the MOS device requires essentially zero power to keep the device on, whereas bipolar devices require a small amount of base-current, typically 100uA or less to drive nixie tubes. Also, various driver chips like the HV5530 are NMOS devices. There are 2 precautions you must observe - Overall circuit-design: Make sure none of the datasheet parameters are exceeded. - Electrostatic discharge (ESD) protection. I dont know what the diode is for; circuit-wise and ESD-wise I dont see any functional purpose for it. Having it there does not cause any problems that I can see. Is the 1meg resistor across the gate-source on the same board as the MOSFET ? If not, then that's most likely the problem because there isn't any path to prevent parasitic charge from accumulating on the MOSFET and destroying it. If the resistor *is* on the same board as the MOSFET, then next thing to consider is how you connect the 2 boards together. It's best to have the grounds connect together first. If you are already doing that, is there anything to protect against excess voltage at the drain, such as a zener-diode or a bleeder-resistor ? I often use 10meg resistors at the drain terminal of high-voltage MOSFET circuits to bleed-off any charge that could try to accumulate during board assembly/handling. What about the power supplies ? Is the LED's power supply the same supply that runs the PWM controller ? If not, that's another potential problem. I doubt you are exceeding the maximum-power dissipation of the device, especially if the LED supply voltage is 12V or less AND the max current is 20mA or less. If either of these values are exceeded, you will need to calculate the power dissipation, and from there, the temperature-rise of the device. Now regarding ESD My workbench has an ESD-mat, I wear an ESD wrist-strap, use an ESD-safe soldering iron, store all of my ESD-sensitive components in conductive bags, store my PC boards in conductive bags once they have sensitive components mounted, and I also have an ESD jack on the PCB that I connect to ground before I remove the board from it's bag. I dont wear a conductive smock (I should), but at least I only wear cotton clothing when handling ESD-sensitive devices. It may sound paranoid, but I've never zapped a device. I realize not everyone can work in these conditions, and if you cant, then at least work on a concrete floor and frequently touch the circuit-ground of your project with your fingers to equalize the potential between yourself and the board. I also suggest touching the circuit ground at the same time you pick-up a conductive ESD bag of parts. I've done this at a minimum for 40 years now and have never zapped a part, even when ESD was not well-understood and many devices had little-or-no internal protection. -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to neonixie-l+unsubscr...@googlegroups.com. To post to this group, send an email to neonixie-l@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/63909f95-1b70-4637-a702-3356ebbecaaf%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
