Hello I'm new to electronics. so i've created a NOT GATE with an NPN transistor like thatenter image description here

Everything works fine for now but what i want is adding a PNP transistor that will be triggered by the NPN one so when i'm not pressing the switch button the NPN will be shut and the PNP works and the opposite when i relase the push button i've made something like that but it's not working enter image description here So how do i made a not gate with both npn and pnp transistors :) Thanks

  • \$\begingroup\$ "I don't know what the problem is" is not a specific enough question, please review the site rules electronics.stackexchange.com/help and look again at how to ask questions. A better question would be: How do I make a not gate with an NPN transistor? This is very specific and it lets people know exactly what you a are looking for without a lot of comments to figure out what you want. Please be more specific and edit the question, Thanks. \$\endgroup\$ – Voltage Spike Apr 26 '16 at 16:59
  • \$\begingroup\$ actually i've made a NOT GATE with an NPN transistor but i asked how to add a PNP transistor with it that will be triggered by the NPN one \$\endgroup\$ – Th3Wolf Apr 26 '16 at 17:01
  • \$\begingroup\$ Yep, I provided an example of a good question please edit your question, Thanks \$\endgroup\$ – Voltage Spike Apr 26 '16 at 17:04
  • \$\begingroup\$ I've changed the question (y) \$\endgroup\$ – Th3Wolf Apr 26 '16 at 17:11

Your problem is that the circuit found it's way through the collector of the PNP transistor, out of the base, and into D1 then to ground, which will also consequently allow current to go through to D2.

Try this.


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  • \$\begingroup\$ I find it hard to understand the transistors LoL what should I do then ? \$\endgroup\$ – Th3Wolf Apr 26 '16 at 16:36
  • \$\begingroup\$ I'm going to make a circuit that will work. It will take a moment. \$\endgroup\$ – Bradman175 Apr 26 '16 at 16:37
  • \$\begingroup\$ Transistors are not enough to make a proper inverting circuit. \$\endgroup\$ – Bradman175 Apr 26 '16 at 16:52
  • \$\begingroup\$ I got a circuit that will work... Well according to my circuit simulator. \$\endgroup\$ – Bradman175 Apr 26 '16 at 16:56
  • \$\begingroup\$ the circuit i'm creating will be for a dc motor controlled by arduino the switch is the signal so when there is no signal i want the motor to turn backwards to close the window and when the signal is sent i want the motor to turn forward to open the window \$\endgroup\$ – Th3Wolf Apr 26 '16 at 16:57
  1. 12 V applied directly to the base of Q1 will result in probably kiloamps or megamps of current flowing through Q1.

  2. -11 V (ish) applied to the base-emitter junction of Q2 will have a similar effect.

    You should be using resistors at the base terminals of these parts to limit the base current.

  3. D1 is holding the Q2 base at about +2 V (so the b-e voltage is about -10 V), even when Q1 is "off". This means Q2 will always be on (very very strongly).

    You could use another PNP transistor (with appropriate base resistor) to decouple the voltage on D1 from the base of Q2.

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  • \$\begingroup\$ Thanks for your answer. Can you please draw this circuit by the way the switch will be a signal from an arduino \$\endgroup\$ – Th3Wolf Apr 26 '16 at 16:51

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