Help Inverting signal for FETs

[turbobill]

Hello Everyone,

I have two physical switches I need to replace with FETs. As it turns out, I'll need four FETs to replace them, here's why.

1,2,3 & 4 are switch positions that I will replace with IRF510 FET transistors. They are controlled by 555 square wave generator. 2&3 will be open when 1&4 are closed when the signal is high from the output of the 555, then when the signal is low they should be the opposite, i.e., 2&3 will be closed when 1&4 are open.

So I am driving the gates with the output of the 555 but but the signal has to be inverted for two of the FETs. I have some 2N2222A transistors that I think will work but I can't figure out how to hook them up. I think there is something about a bias, but that's where I'm lost.

Any help is much appreciated.

Thanks,
TurboBill

 

[Hero999]

Please post a schematic.

If the switches are on the low side they need to be N channel and if theiy're on the high side they need to be P-channel.

 

[rezer]

Hello Everyone,

I have two physical switches I need to replace with FETs. As it turns out, I'll need four FETs to replace them, here's why.

1,2,3 & 4 are switch positions that I will replace with IRF510 FET transistors. They are controlled by 555 square wave generator. 2&3 will be open when 1&4 are closed when the signal is high from the output of the 555, then when the signal is low they should be the opposite, i.e., 2&3 will be closed when 1&4 are open.

So I am driving the gates with the output of the 555 but but the signal has to be inverted for two of the FETs. I have some 2N2222A transistors that I think will work but I can't figure out how to hook them up. I think there is something about a bias, but that's where I'm lost.

Any help is much appreciated.

Thanks,
TurboBill

If your just using these FETs as switchers:

You could try just a 2n3904. The 2n2222 is a little over-kill and the DC current gain is not as high.

The pin out for the 2n3904 is:
pin 1 = emitter, connect to ground
pin 2 = base, connect to pin 3 output of 555 timer through a series 1KΩ resistor.
pin 3 = collector, connect to gate of FET with a 470Ω pull-up resistor.

 

[turbobill]

If your just using these FETs as switchers:

You could try just a 2n3904. The 2n2222 is a little over-kill and the DC current gain is not as high.

The pin out for the 2n3904 is:
pin 1 = emitter, connect to ground
pin 2 = base, connect to pin 3 output of 555 timer through a series 1KΩ resistor.
pin 3 = collector, connect to gate of FET with a 470Ω pull-up resistor.

I don't have any 2n3904's right now, so do you think these values will work with the 2n2222 or would I need to bump up the values a bit? If so, how much?

Is there a simple formula to compute those values?

Thanks

 

[rezer]

I don't have any 2n3904's right now, so do you think these values will work with the 2n2222 or would I need to bump up the values a bit? If so, how much?

Is there a simple formula to compute those values?

Thanks

What voltage is Vcc?

Yes. The following values are based on a 5V supply for Vcc.
The 2n2222 pin-out is:
pin 1 = base, wired to output of 555 timer with 10KΩ series resistor in-line from output to base.
pin 2 = emitter, connect to ground
pin 3 = collector, connect to gate of FET with a 220Ω pull-up on the gate of the FET.
These values are approximations. You can use something close in value and it will be fine.

 

[turbobill]

What voltage is Vcc?

Yes. The following values are based on a 5V supply for Vcc.
The 2n2222 pin-out is:
pin 1 = base, wired to output of 555 timer with 10KΩ series resistor in-line from output to base.
pin 2 = emitter, connect to ground
pin 3 = collector, connect to gate of FET with a 220Ω pull-up on the gate of the FET.
These values are approximations. You can use something close in value and it will be fine.

Voltage for Vcc is 12V, how would I compute new values?

Thanks a bunch for your help.

 

[rezer]

What voltage is Vcc?

Yes. The following values are based on a 5V supply for Vcc.
The 2n2222 pin-out is:
pin 1 = base, wired to output of 555 timer with 10KΩ series resistor in-line from output to base.
pin 2 = emitter, connect to ground
pin 3 = collector, connect to gate of FET with a 220Ω pull-up on the gate of the FET.
These values are approximations. You can use something close in value and it will be fine.

At a Vcc of 12V
Use a 1KΩ resistor on the base of the 2n2222 (This will ensure saturation). You can stay with the 470Ω on the gate.