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I have thoroughly checked the forum and I am not 100% sure which specific part (if any) can perform what I wish. I wish the opposite of what the PN2222 transistor performs. I want the +3v from a battery to pass through when there is zero voltage at "base".

So please tell me if I can perform this with the PN2222 I already have or please tell which part in particular I should acquire (small sized like the PN2222).

Thank you and excuse me for my ignorance.

EDIT: My input is voltage to a little speaker; instead of the speaker I wish to use the voltage to trigger an RF transmitter that uses a 3v voltage. Problem is that I wish to initiate the switch (ON) when the voltage is low (around 0,3v) and to be OFF at higher voltage readings.

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    \$\begingroup\$ What forum? SE isn't a forum BTW. Regards your question, state what you want to happen and define where the control voltage comes from and how it is connected with the battery. Load current should also be specified. Please don't try and describe it by saying it's the opposite of a PN2222 because that leads to ambiguity or confusion. \$\endgroup\$ – Andy aka Aug 2 '18 at 10:32
  • \$\begingroup\$ You can use an inverter ic with the output of the transistor. \$\endgroup\$ – Ahmed M.Zahran Aug 2 '18 at 10:43
  • \$\begingroup\$ I think you've had enough time to sort your question out. \$\endgroup\$ – Andy aka Aug 2 '18 at 12:52
  • \$\begingroup\$ You may be able to find a depletion mode FET that might work but they are less common. \$\endgroup\$ – KalleMP Aug 2 '18 at 18:02
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It sounds like you want a PNP transistor.

Don't worry about whether it is complementary ("Opposite" is way too ambiguous. What parameters are opposite? The pin order? The case color?) to a particular NPN transistor, because you don't seem to have a specific need for your particular NPN in the first place.

Define the specs for what the transistor needs to do, then go from there looking for the appropriate part. At minimum, you need to know the maximum voltage it must be able to withstand, and the maximum current it must be able to carry. Your circuit will have a minimum gain requirement. After that, find the worst case power it will need to dissipate. Those parameters are probably enough to find a suitable part.

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Do you mean something like this: NPN Of course you'd need to adjust the values of the resistors according to your LOAD and what you put on the INPUT. The ground (GND or -) of the INPUT needs to be connected to the - of the BATTERY, otherwise it will not work.

You could also try the schematic below. It is more simple, but you will need a different transistor for it to work. The PN2222 you talked about is a NPN type. For this schematic you will need a PNP type. A PN2907 might work as some already mentioned, but it depends on your LOAD. PNP

This might ask a little more current from your INPUT though. You also still need to calculate good values for the resistors.

So how to calculate what resistor values you need, and what schematic will work best for you? Wel, first we need more information from you, otherwise we/you can't calculate anything. What you need to tell us is this:

  • What kind of load do you want to power? Is it a light bulb, or an LED, or a relay, or a small motor, or... And you need to tell us how much current will flow through the LOAD when you put 3V on it. If you don't know, we might be able to guess how much, depending on what it is :-)
  • You need to tell us what's on the INPUT as well. Is it a battery, or a switch, or something else? How much current can be drawn from the INPUT? Because depending on the INPUT, the schematic might need to have some small adjustments.

It's probably not possible to create what you want with just one PN2222 that you already have. Unless your LOAD is something I didn't expect it to be... haha.

Edit: Added PNP variant and some extra info.


Edit: New information used to create schematic

You could try this: Try2 I can't guarantee that it will work, because I don't know anything about your speaker, and you didn't answer how much current your RF module uses. Good luck.

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  • \$\begingroup\$ OMG, I can't consume all trese technical stuff! My PN2222 is normally open now - I want to make it normally closed, I hope there is a quicker easier way to do this. \$\endgroup\$ – Alexios Aug 2 '18 at 11:05
  • \$\begingroup\$ why should there be an easier way? This is really easy. The first PN2222 just "inverts", the second "inverts" again. \$\endgroup\$ – Marcus Müller Aug 2 '18 at 11:58
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    \$\begingroup\$ @Alexios All this technical stuff? This answer provides a very easy way to do what you need. If this is too much for you to understand, you should reconsider designing anything till you have got a bit more knowledge behind you. Also, you really need to be more specific in your question. Give us a schematic of what you have and explain what you want to happen, when, and how. Also load is important too. You have missed a lot of information out \$\endgroup\$ – MCG Aug 2 '18 at 12:01
  • \$\begingroup\$ Input 5.5v. Load 3v. Battery 3v. If I know how to calculate the resistors then possibly I will be able to replicate the diagram provided above. Grateful in any case. \$\endgroup\$ – Alexios Aug 2 '18 at 14:24
  • \$\begingroup\$ Thank you for the diagram with PN2907. What resisitors can be used with the first diagram (with PN2222)? \$\endgroup\$ – Alexios Aug 2 '18 at 19:33

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