Best/Cheapest high power linear mode mosfet  - Page 1
Forum section: electronics / projects

author: Miyuki
author_rank: Frequent Contributor
timestamp: November 14, 2020, 06:39:35 pm
content: Hi folks,just looking for linear mode MOSFET with best power/price ratingI need at least 400V and want a total capability of 1000WNow it looks like the best choice is IXTH6N50D2 with a price of 6$ and linear SOA 180W at TC = 75°C (depletion or enhanced mode makes no difference)Most linear rated ones look even more expensive.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 14, 2020, 06:58:35 pm
content: FQA9N90C last I checked.I made this, would you be interested?https://www.seventransistorlabs.com/Images/ActiveLoad1.jpgTim

author: Miyuki
author_rank: Frequent Contributor
timestamp: November 14, 2020, 07:40:54 pm
content: Quote from: T3sl4co1l on November 14, 2020, 06:58:35 pmSome nice electronic load? Tell me moreHow much you derate them for linear operation?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 14, 2020, 09:19:33 pm
content: The row without heatsinks, switches a bunch of power resistors -- more compact and reliable than heatsinks, though whether it's less hardware or BOM cost overall is yet to be seen...Tim

author: Weston
author_rank: Regular Contributor
timestamp: November 15, 2020, 12:33:09 am
content: Quote from: T3sl4co1l on November 14, 2020, 09:19:33 pmI believe some of the Magna Power do something like this, where they have a set of resistors they can switch in and out, and a smaller linear load using some active device that fills in between resistor ranges. It must make economic sense for them, but they build multi-kw level loads.I bet it simplifies thermal design too, as resistors have less thermal derating than semiconductors.

author: sorin
author_rank: Frequent Contributor
timestamp: November 15, 2020, 12:56:37 am
content: The SOA can't tell you very much. Thermal Resistance and Mosfet voltage are also important.

author: Vovk_Z
author_rank: Super Contributor
timestamp: November 15, 2020, 02:27:00 pm
content: About $10 ones: FDH44N50, IXFH44N50P (IXFK44N50P), IXFH20N100P, IXFH30N50Q3 (it was vey brief search, so look carefully at them).And the most powerful one at about $15: FDL100N50F. This one can stand 400V 1000W with only two cases needed.

author: sorin
author_rank: Frequent Contributor
timestamp: November 15, 2020, 02:36:26 pm
content: TO-264 at max can handle 200-300W

author: Miyuki
author_rank: Frequent Contributor
timestamp: November 15, 2020, 03:37:59 pm
content: Quote from: T3sl4co1l on November 14, 2020, 09:19:33 pmFor switched load I consider light bulb rather than resistors, it is much smaller for a given power and also is cheaperLike 5$ for E40/500W/230V bulbor E27/100W/24V cost about 2$ and can connect them in serial or parallel wayand then connected with the linear regulating stage

author: langwadt
author_rank: Super Contributor
timestamp: November 15, 2020, 03:42:23 pm
content: Quote from: Miyuki on November 15, 2020, 03:37:59 pmbut very low resistance when cold

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 15, 2020, 08:36:33 pm
content: Exactly. In fact, you can't know the instantaneous resistance of a lamp until it's turned on -- at which point you may be drawing too much current to adjust downward with the linear sink. Then in the milliseconds it takes to heat up, current drops considerably, and more lamps need to turn on, or the linear sink has to throttle up to compensate. Even with feedback loops, it's a mess to control.But we can easily solve the case for reasonably stable resistors -- a little offset to keep resistors off until some minimum current drawn by the linear sink, and using the linear sink to servo total current. As long as the resistors are within the design nominal range (say 10% or whatever), it's good. The linear sink may even be fast enough to smooth out switching edges from the resistors going on and off, giving a continuous transfer function.Indeed, the function is so simple, it can be calculated with a simple unary ADC -- the LM3914. Or, it was until it went obsolete a few years ago.An MCU can easily substitute of course, albeit at the expense of response time. Required is 2 x ADC samples, filtering, a division, and propagation to outputs: with a typical ATMEGA324 say, that'll be some tens or hundreds of microseconds, depending on how fast the ADC can run. Whereas the 3914 settles in a microsecond or so.Tim

author: Miyuki
author_rank: Frequent Contributor
timestamp: November 16, 2020, 11:06:10 am
content: Ok its a destiny, on local bazar is resistive load made with six 11 Ohm 200W resistors for almost nothingCan you please help me with the best switching scheme/network to switch six resistors from parallel to serial in small steps?