Timeline for MAX712 charging circuit - diode gets too hot
Current License: CC BY-SA 3.0
9 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| May 14, 2017 at 9:23 | comment | added | Joren Vaes | The 5 kelvin per watt is from the heatsink itself - the heatsink will become 5 kelvin more above ambient with every watt of power extra being pumped into it. However, inside the transistor, the heat first needs to go from the silicon die to the metal tab on the transistor (this is what we call the junction-to-case thermal resistance). This causes an extra increase in thermal resistance. If you want more information, Dave L. Jones from the EEVBlog has a good video on the topic: youtube.com/watch?v=8ruFVmxf0zs | |
| May 14, 2017 at 9:21 | comment | added | Leonti | @JorenVaes Max current will always be 1A, max voltage drop is 9V What values the resistors should be? | |
| May 14, 2017 at 9:19 | comment | added | Leonti | Also where is 3k/W comes from in "The Transistor" section? I understand 45 degrees (5*9) + 20 degrees ambient, where another 20 come from? By the way, awesome answer, many thanks :) | |
| May 14, 2017 at 9:19 | comment | added | Joren Vaes | Depending on how the circuit works, and what you are expecting in terms of input and output and current range, you can sometimes put a series resistor in front of the transistor to take some of the load on it. (You will still disipate the same amount, but it will be spread out over more components). A bigger transistor and bigger heatsink is also possible, or two transistors (With two heatsinks - otherwise you are not gaining anything significant) with some emitter degeneration could also work. | |
| May 14, 2017 at 9:16 | comment | added | Leonti | Thanks, now I understand. Calculating heat dissipation is something new to me, so I didn't know what to expect, so when things get too hot I automatically assumed that I made a mistake in my circuit. Glad to know that's not the case. So what are my options? Should I just get a bigger heatsink and replace diode with the Schottky diode as @metacollin suggested? | |
| May 14, 2017 at 9:12 | history | edited | Joren Vaes | CC BY-SA 3.0 |
deleted 1 character in body
|
| May 14, 2017 at 9:09 | vote | accept | Leonti | ||
| May 14, 2017 at 9:08 | comment | added | metacollin | Have an upvote for actually doing some math (unlike my answer) :) | |
| May 14, 2017 at 9:01 | history | answered | Joren Vaes | CC BY-SA 3.0 |