how to start with power transistors? - Page 1
Forum section: electronics / beginners

author: 001
author_rank: Super Contributor
timestamp: September 23, 2018, 02:21:23 pm
content: how to start with power transistors?voltage and surrent sources, darlingtons etcthanx

author: Zero999
author_rank: Super Contributor
timestamp: September 23, 2018, 06:55:19 pm
content: Quote from: 001 on September 23, 2018, 02:21:23 pmBe more specific.What project are to trying to build?A power transistor needs to have a good enough heatsink to avoid overheating. The key to thermal design is understanding the thermal resistance specified inoC/W, i.e. a heatsink with a thermal resistance of 1oC/W, will raise its temperature by 1oC above ambient, for every Watt of power produced by the power device attached to it. Transistors also have a thermal resistance specified between the junction and case, which works on the same principle and the same goes for thermal pads. The thermal resistances of the heatsink, transistor's junction to case and thermal pad all add together. For example, if a transistor has 10V across it, the current is 1A, the power dissipation will be 10W. If it has a maximum junction temperature rating of 120oC and the maximum temperature of the environment, where the circuit will work is 40oC, then the maximum permittable temperature rise is 120-40 = 80oC. The maximum thermal resistance between the transistor's junction and ambient is 80/10 = 8oC/W. If the transistor has a thermal resistance of 3oC/W between the junction and case, the maximum permissible thermal resistance of the heatsink and thermal pad is 8-3 = 5oC/W.Another issue is the device's safe operating area, which greatly reduces the device's maximum power rating, at higher voltages, especially with BJTs.https://en.wikipedia.org/wiki/Safe_operating_area

author: 001
author_rank: Super Contributor
timestamp: September 23, 2018, 11:11:32 pm
content: YeaThanxWhere I can read some tutorial specially for power electronix?

author: Sceadwian
author_rank: Unknown
timestamp: September 24, 2018, 12:20:37 am
content: Your question is too vague, Hero999's general suggestion to learn how to interpret thermal considerations is probably the most important thing to learn. You're going to have to be more specific then that as all the consideration of general electronics apply to power electronics.There are device and application specific problems that could occur such as DV/DT latching of power Mosfets as one example. It depends too heavily on your specific usage.https://www.ixys.com/Documents/AppNotes/IXAN0061.pdf

author: Zero999
author_rank: Super Contributor
timestamp: September 24, 2018, 09:21:09 am
content: Quote from: 001 on September 23, 2018, 11:11:32 pmFar too vague. What aspects of power electronics are you talking about?My previous post dealt with thermal design, especially of a linear device, because it's where most newcomers start. A switching element is a bit more complex, especially if it's working at a high frequency, where the switching losses will be significant.

author: xavier60
author_rank: Super Contributor
timestamp: September 24, 2018, 09:57:52 am
content: Quote from: 001 on September 23, 2018, 02:21:23 pmDo you want to do some experiments? You could start with a simplezenner and series pass transistor regulatorDo you have a safe unregulated power source?

author: xavier60
author_rank: Super Contributor
timestamp: September 25, 2018, 01:53:06 am
content: Rs can then be replaced with a constant current source to improve the performance.

author: GeoffreyF
author_rank: Regular Contributor
timestamp: October 12, 2018, 01:34:22 pm
content: I would suggest that you start with low power ones. The principles are all the same. All the types of circuits you mentioned can be explored with low voltages and currents. The costs of projects, of mistakes are less. If you are exploring higher power, there are also more issues with heat dissipation and even with fire.