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| High efficiency DIY buck converter |
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| Siwastaja:
P = I^2 * R. Assuming MOSFET switch, do note that R is specified at die temperature of 25 degC. At, say, 100 degC die temperature (case temperature can be much less), it's about 1.5 times higher. Also remember to provide high enough gate voltage to minimize Rds(on). For a buck, a separate switch usually won't make sense (the buck itself has the switch); use a buck chip/module with enable input instead. |
| drummerdimitri:
--- Quote from: Siwastaja on September 21, 2019, 04:49:48 pm ---P = I^2 * R. Assuming MOSFET switch, do note that R is specified at die temperature of 25 degC. At, say, 100 degC die temperature (case temperature can be much less), it's about 1.5 times higher. Also remember to provide high enough gate voltage to minimize Rds(on). For a buck, a separate switch usually won't make sense (the buck itself has the switch); use a buck chip/module with enable input instead. --- End quote --- You misunderstood. Sorry for the ambiguity, I was referring to a physical ON/OFF switch not a transistor. |
| Siwastaja:
--- Quote from: drummerdimitri on September 21, 2019, 05:00:18 pm --- --- Quote from: Siwastaja on September 21, 2019, 04:49:48 pm ---P = I^2 * R. Assuming MOSFET switch, do note that R is specified at die temperature of 25 degC. At, say, 100 degC die temperature (case temperature can be much less), it's about 1.5 times higher. Also remember to provide high enough gate voltage to minimize Rds(on). For a buck, a separate switch usually won't make sense (the buck itself has the switch); use a buck chip/module with enable input instead. --- End quote --- You misunderstood. Sorry for the ambiguity, I was referring to a physical ON/OFF switch not a transistor. --- End quote --- P = I^2 * R still applies. Although, for mechanical switches, the ratings are all over the place, and the actual R is more unpredictable. Some quote a "cold resistance" and then "voltage drop at rated current", which gives you a different R when you calculate R = U/I. |
| NiHaoMike:
If the converter has a low enough shutdown current, you can just use a signal level switch to disable it. |
| SiliconWizard:
--- Quote from: drummerdimitri on September 20, 2019, 07:46:27 pm ---Sorry for my initial ballpark guess. I thought the energy wasted was a lot higher than actual since the heatsink of the power transistors reaches 60C after some time and stays at that temperature. I did some efficiency calculations and it is actually around 93.5% which is really good! (...) so Should I try mounting those transistors onto larger heatsinks? --- End quote --- So, exactly what I suspected! ;D And yes, you need to improve heat dissipation. And if your enclosures have no vents (or too small ones), it's going to get pretty hot in them no matter how large the heatsinks. |
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