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  • rkondner commented on baelza.bubba's instructable 12V NE555 PWM Controller Under $33 months ago
    12V NE555 PWM Controller Under $3

    Hi, I have used 555 devices for a long time and the part you are calling out is, I believe, a bipolar parts They also make CMOS version of the part and I find them very superior.The 555 outputs will drive a FET fine at low frequencies which is probably ok in this application. For higher powers / voltages you might try a CMOS device or get a FET driver. What I have seen in 555 outputs is a small glitch in the output where both the pull up and pull down transistors are both off. Bipolar transistors exhibit storage times and IC designers make darn sure there is a dead time when both transistors are off. Both being in a conducting state at the same time is very bad. CMOS transistors do not have a storage time. This output glitch could result in large switching loss. Also, reconsider the 100...see more »Hi, I have used 555 devices for a long time and the part you are calling out is, I believe, a bipolar parts They also make CMOS version of the part and I find them very superior.The 555 outputs will drive a FET fine at low frequencies which is probably ok in this application. For higher powers / voltages you might try a CMOS device or get a FET driver. What I have seen in 555 outputs is a small glitch in the output where both the pull up and pull down transistors are both off. Bipolar transistors exhibit storage times and IC designers make darn sure there is a dead time when both transistors are off. Both being in a conducting state at the same time is very bad. CMOS transistors do not have a storage time. This output glitch could result in large switching loss. Also, reconsider the 100 ohm gate resistor. Typically 5 ohms is plenty and I worry that 100 ohm would introduce high switching loss. I noticed a small heatsink on your FET. Going to a CMOS parts and dropping the gate resistor could make a big difference. I would love to hear if that helps.And be sure to hang a scope on the drain, I always check for stray inductance requiring a snubber. Take a look at the FET switch in the SunDuino schematic I used in some power supply designs, you will see examples of what I am suggesting. (www.sunduino.com) Be sure to post what you try, I am curious if you can drop loss to where that heatsink is not required!Thanks, Bob K.

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