Want FET Which Can Give ID as 5A

"There are very few power mosfets that _can't_ do 5A. It's been suggested that you check the IR site. You can also do well to visit Fairchild, Vishay, Infineon, NXP and ST."

Actually, that's not how I select parts when I'm designing, or when I'm making a selection table for AoE III, for that matter. I keep a pretty complete set of all the datasheets I can find on my computer, but I don't go there either. Instead, I fire up a distributor website, one that has a good search engine, and I look for inexpensive popular parts, with lots of inventory in stock, and hopefully parts that are second sourced. If I find a jellybean part, it'll be easier to get and be around longer - what a pain when you choose a part and it disappears after a few years! OK, let's do an example using Ejaz484's requirement for a 5A MOSFET. Open a new browser window and follow along.

I find Mouser's search engine especially useful (you don't have to be buying from them, but instead you're using them as a research tool). There are several ways to get started. For example, we could search on MOSFETs. Instead, let's click on Discrete Semiconductors and then Transistors General Purpose (with 30,465 items) and then MOSFET Power (11,768). Aha, now we can begin to narrow things down. Under Configuration select Single, under Polarity select N-channel, and click the Apply Filters button. At this point Mouser tells us we have 7720 remaining parts, and displays a detailed list. But we're not anywhere near ready to look a specific parts yet.

Let's move to the right and under Mounting Style, select Through Hole, and click Apply Filters to narrow the choices. Under Package / Case we'll move down and click on the first TO-220 choice. Operate the scroll bar (click the down arrow), moving the list to show the last TO-220 choice, which is TO-220SIS, whatever that is! Hold the SHIFT key down and click on that one. This select all the TO-220 choices, and now we have 2020 remaining parts, and only 81 pages. :-)

Aha, we forgot to click in the "stocked" button, but not to fear, we can do that at any point. OK, this is better, now we have 705 remaining choices and we're ready to do some serious work.

Under Continuous Drain Current let's start at 20A and select from 20A to 50A. Clicking Apply Filters, we have 122 parts left. Drain-Source Breakdown Voltage is next, we'll select 55 to 100 volts, leaving 57 matching parts.

We need to discuss the MOSFET current rating spec: this is based on the maximum current I_D that dissipates the maximum-allowed power P_D, forcing the semiconductor junction T_J to its maximum value (e.g. 150°C), assuming a 25°C case temperature T_C. But, first, we don't want T_J to reach 150°C, and second we can't keep T_C at 25°C, and third the switch-resistance R_DS(on) will go up by about 1.5x as the junction temperature rises. Furthermore, we don't want the MOSFET when used as a switch to significantly warm up, because then we'd need to add a heat sink. The bottom line is we can't continuously operate the MOSFET anywhere near the overly-high Continuous Drain Current value. (This is merely a useful number for comparing parts, etc.) That's why we select for up to 50A parts when looking to fill a 5A requirement.

As for voltage, 55 to 75 volts is the sweet spot for automotive parts, with more choice and better prices. If we can use a part of this type, that's good.

Now the fun part, where we look for a low-cost popular part. Under Pricing (USD), click the ^ arrow, to sort by lowest-cost first. Another important parameter is Availability, so we'll keep our eyes on that along with price.

Mouser has a convenient Compare Selected button, where you can check the left-hand boxes for candidate parts. But we have three pages of choices, and unfortunately, SFAICT, the parts you check on one page become unchecked when you move to a second page. So instead we'll build a little table, going for cheap parts with a significant inventory, and more expensive parts with massive inventory. The first part is an IPP50CN10NG, with 745 in stock, costing 57 cents, and with R_DS(on) = 50mΩ. The first two parts will dissipate P_D = I² R = 5² • 0.05 = 1.25W at 5A, assuming a 25°C case, or closer to 1.9W, if it heats up significantly. That's nearing the upper edge of OK, without a heatsink.

Once you find parts that look interesting, you can click their name to get their own catalog page, and quickly download a datasheet.

As I scanned Mouser's list, I saw that many popular familiar parts are "On Order" - for example, the FQP20N06L has 13900 on order. This is a nice part, because it's a logic-level type, having 55mΩ of on-resistance with 5-volt gate-voltage drive, instead of the usual 10 volts. You can click View Delivery Dates and you get a list of Mouser Product Availability showing 2900, 3000, 2000, and 6000 parts, with the earliest Estimated Ship Date of 2/23/2011. Bummer.

Once you've located some candidate parts, you can check other distributors. For example, searching on IRF540 (taking only the main portion of the p/n), we see that DigiKey has 8188 of the IRF540Z variant in stock, starting at $1.70 each.

• IRF540ZPBF 8188 $1.70 100 0.027