Using an NMOS as a switch for a 10V DC source in a 555 timer circuit

I used NI multisim and created a circuit with a 555 timer that will allow a diode to flash at a frequency of about 4HZ. This is the circuit:

As you can see in the above image, the oscilloscope graph is a square wave constantly changing from high to low which means the light is flashing on and off. Nothing wrong with this.

After that, I tried to make a simple modification to the circuit by adding in an NMOS as a switch for the 10V DC source. In the image below, I am pretty sure that I set up the NMOS correctly. I'm feeding the gate of the NMOS a voltage of 0V. You'd expect the output of the oscilloscope to be a flat horizontal line at y=0 which means that no current/voltage is reaching the diode. However, this does not happen. I see the same square wave from before.

I hope the images are clear enough. I am unsure what I have done wrong. Any help would be greatly appreciated. Thank you!

• Hmm, it looks to me like your NFET will just short the power supply and blow up if you turn the gate on. Otherwise it makes no difference to the circuit. It should be in series with the 10V supply, and then you will need a voltage somewhat higher than 10V to turn it fully on. Nov 11, 2020 at 0:41
• So you're saying that the NFET/NMOS should be in series with the 10V supply? I thought this was already the case in my circuit. Is it possible that you could show me a diagram so I can see what you mean. As in, how it would look like once it has been implemented. Thanks. Nov 11, 2020 at 1:11
• Could you describe how you see the NMOS working in your circuit? What exactly do you intend for it to do and how? Nov 11, 2020 at 1:11
• Hi brhans. The idea is that if I'm giving the NMOS a gate voltage of 0V, then it should act as an open circuit to the 10V source and current is not allowed to flow from it. Is that not how an NMOS works? It acts as an open circuit for a low gate voltage and acts as a closed circuit for a high gate voltage. Nov 11, 2020 at 1:15
• R3, R4 and Q1 are not connected to the 555 timer circuit ... they only share a power supply Nov 11, 2020 at 2:07