Timeline for Buck converter MOSFET (IRF4905) heating up
Current License: CC BY-SA 4.0
19 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Dec 24, 2019 at 12:16 | answer | added | Wonka | timeline score: 4 | |
| Dec 17, 2019 at 3:36 | comment | added | Russell McMahon♦ | Here's a 2001 discussion of 'my' GSR = God's Switching Regulator - there's a story in that , and 2011 continuation - scroll down for a bipolar version that appeared on web some time after mine. | |
| Dec 17, 2019 at 3:32 | comment | added | Russell McMahon♦ | For interest: I long ago designed a converter essentially the same as this in principle that was used in volume production. It worked very well. I had a few special needs that made nothing available commercially suitable. (~= Zero cost being one :-) ). Also Vin = 12-200V+ DC and 12V out - a spec most suggest is not possible. It is :-). I used a zener in series with R3 and large R4 so the zener and not the divider did the V setting. Hysteresis is provided by the L1C1 per cycle ripple - a VERY small R in series with Iout after the R3 tapoff can help hysteresis but probably unneeded. | |
| Dec 17, 2019 at 3:24 | comment | added | Russell McMahon♦ | Try adding some formal hystereis between points that move with the same polarity during switching eg between Q4b - Q5C. Small capacitor or perhaps resistor or some combination. | Perhaps Q5c - Q1s but that may get 'interesting'. | In similar all discrete real world desins this has helped considerably. | |
| Dec 16, 2019 at 18:51 | answer | added | D.A.S. | timeline score: 1 | |
| Dec 16, 2019 at 17:44 | comment | added | D.A.S. | The MOST critical parts not specified are the diode and heatsink. Due to loop gain and Q , this will change performance alot. Is there a heatsink? Remove the cap to make it oscillate better | |
| Dec 16, 2019 at 17:05 | answer | added | rdtsc | timeline score: 1 | |
| Dec 16, 2019 at 16:25 | answer | added | Hearth | timeline score: 0 | |
| Dec 16, 2019 at 16:03 | answer | added | Andy aka | timeline score: 4 | |
| Dec 16, 2019 at 15:39 | comment | added | TimWescott | Note that if you live in a 1st-world country you're going to spend more money on the extra circuit board space than you would on some 20 year old jellybean switcher chip, like an MC33063 -- and the chip will perform better. Note, too, that if you're willing to do surface-mount, you'll spend less money on a brand new switcher chip that operates at 200kHz to 1MHz than you will on the inductor you'll need for a 40kHz, 10W switcher -- it's why the new chips sell. | |
| Dec 16, 2019 at 15:35 | answer | added | TimWescott | timeline score: 1 | |
| Dec 16, 2019 at 15:30 | comment | added | TimWescott | "OK, I will try to use the terms properly next time." To avoid confusion (because you're not the only one who uses "reverse terminology") I try to stick with "on" and "off" -- that's pretty unambiguous. | |
| Dec 16, 2019 at 15:21 | comment | added | Bimpelrekkie | The heating up of the P-MOSFET should not happen provided that it is switched on/off properly and quickly enough. Use an oscilloscope to monitor the Vgs of Q1. Also make sure that inductor L1 doesn't saturate. These are standard checks on any DCDC converter. I must state that it will be challenge to make a "good" 2A DCDC converter using only discrete components. | |
| Dec 16, 2019 at 15:16 | comment | added | Wonka | OK, I will try to use the terms properly next time. The transistor reaches 100°C in about 2 minutes. I used a schottky diode meant for switching power supplies (SR***). I'm not quite sure which one it is because I currently don't have the circuit near me. The inductor is a 100uH ferrite core inductor pulled from an old PC power supply. I later tried switching it for a 280uH toroidal core inductor. | |
| Dec 16, 2019 at 14:54 | comment | added | Andy aka | When EEs refer to opening and closing circuits we do it oppositely to that which a plumber might say thus, if a transistor "opens" it stops conducting and vice versa. Hence we have an open circuit that means there is no connection. Did it become too hot to touch? Heating up is expected. What flyback diode did you use? What inductor did you use? | |
| Dec 16, 2019 at 14:43 | comment | added | winny | Welcome to EE.SE! Please show Vgs and Vds in the same oscillogram with good probing. You can’t develop an SMPS without an oscilloscope. | |
| Dec 16, 2019 at 14:41 | history | edited | SamGibson♦ | CC BY-SA 4.0 |
Added link to datasheet. Fixed typos and small grammar changes to help readability.
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| Dec 16, 2019 at 14:35 | review | First posts | |||
| Dec 16, 2019 at 20:42 | |||||
| Dec 16, 2019 at 14:34 | history | asked | Wonka | CC BY-SA 4.0 |