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Some days ago I was considering using a small signal P-Channel MOSFET in a design of mine, but could not find a suitable part.

The specs I was looking for were something like the following:

  • \$I_D = -500mA\$ (continuous drain current)
  • \$V_{GS} = -5V\$ (gate-source voltage, for \$5V\$ logic level)
  • \$V_{DS} = -12V\$ (drain-source voltage)

I was expecting to find a popular P-Channel counterpart of N-Channel 2N7000 or BS170 in a TO-92 package, that may be in everybody's bins, just like BJT NPN/PNP pairs BC547/557 and BC337/327, but could not find it. I could just find vendor specific P-Channels in SMD packages.

Is there a popular counterpart for 2N7000 or BS170? If not, why not?

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    \$\begingroup\$ 2n7000 / BS170 is a relic of the past when MOSFET performances were far lower. It is far better to find a more modern FET with better specs and its complement. In particular the 2N7000 turn on voltage (Vth or Vgsth or ...) is marginal at 5V and unsuited to 3V operation and it Rdson (on resistance) can be bettered by a piece of wet string soaked in weak brine. Try using eg Digikey's selector guide to find parts that suit your need. \$\endgroup\$ – Russell McMahon Apr 29 '14 at 19:57
  • \$\begingroup\$ @Russel - I estimate that my homemade PCB production process uses technology equivalent to that of the end of the 70's. Thus my question. But I really need to move towards something more modern, so thanks for the hint. \$\endgroup\$ – Ricardo Apr 29 '14 at 20:05
  • \$\begingroup\$ If you want a PFET that is almost as horribe as a 2N7000 there is the SOT23 NXP nx3008(Http://www.nxp.com/documents/data_sheet/NX3008PBK.pdf) for about the same price, and the 20V rated but otherwsise utterly superior (also SOT23) [A03415 for slightly more (19c/100 at Digikey). \$\endgroup\$ – Russell McMahon Apr 29 '14 at 20:11
  • \$\begingroup\$ @RussellMcMahon - if you could give specific suggestions for modern equivalents, that would be great. There's a question here that asks for replacements, but none of the answers there are actually available here. \$\endgroup\$ – TLW Dec 28 '16 at 21:05
  • \$\begingroup\$ @TLW Where is "here". Digikey supply in many places - sometimes with "virtual presence"- ie what looks like a a national site but delivered from elsewhere. Their selector guide is a good way to find suitable parts for which local availability can then be checked. || The AO3415 looks rather good compared. I'd expect the BS250 to be widely available. \$\endgroup\$ – Russell McMahon Dec 28 '16 at 23:10
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That is called a complementary transistor.

BS250 is complementary to 2N7000.

Check this list for PFETs with the characteristics you want. However I don't know what popular transistors you'll find there.

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  • \$\begingroup\$ It's good to know how these pairs are called. That makes it easier for me to google. The link you posted is also really useful. Many thanks! \$\endgroup\$ – Ricardo Apr 30 '14 at 12:25
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ZVP3306A is not too bad a choice as a complimentary part to the 2N7000, rather cheaper (~30%) than the BS250, but it is still more than six times more expensive than the surface mount SOT-23 BSS84.

The 2N7000 is not good for 500mA, so you're not really looking for the equivalent (and you'll probably be pushed out of a TO-92 package into a TO-220 such as the IRLIB9343PBF if you insist on through-hole).

Again, if you are willing to use SOT-23, you can get a part that meets all your other requirements for less than 1/10 the price... for example the AO3403, which is almost magic- 30V, 2.6A, and it turns on quite well (200m\$ \Omega\$) with only 2.5V. Only problem it that it is SOT-23.

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    \$\begingroup\$ Thanks Spehro! Very useful answer, as usual. That reiterates the need for me to start using surface mounted devices. \$\endgroup\$ – Ricardo Apr 30 '14 at 12:26
  • \$\begingroup\$ Found a similar part that is even cheaper with lower on resistance. -20V, -2.2A, RdsOn=70mOhm, partno FDN340P can be found for $0.1 / piece on ebay. \$\endgroup\$ – nagylzs Dec 30 '18 at 9:30
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Consider the design to be sustainable, 2N7002 usually is used to control signals. You can use BSS84 as equivalent but pmos usually is used as power switch. that's why people rarely can find 2N7002's equivalent. They just use 2n7002 to turn on a PMOS power load switch.

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    \$\begingroup\$ Please use proper punctuation, these questions are searchable by google and it would be nice if they looked nice. \$\endgroup\$ – Voltage Spike Aug 8 '16 at 22:00

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