TBH, MosFETs that turn on 12 V Drain to Source on a 3.3V Gate signal, are from a conventional perspective very special.
That is, from all I know, a common MosFet has already a Gate to Source drop of 1.5 to 2V, meaning you have 12V at the Drain, 3.3 at the Gate and end up with 1.8 V at the Source - barely enough to light up an LED.
However, you can use a MosFET in inverting mode, and then you can unleash all the 12Volts with a 3.3V signal, with most MosFETs.
Adding another MosFET inverts it back to normal.
There is a 100k ish resistor between VCC and the drain. Whenever the signal at the gate is low, no current can flow, hence Kirchhoffs law does not apply and we read 12 V between the drain and the 100k resistor. If the signal at the gate goes to 3.3 V, some current will flow from Drain to source, which causes the 100K resistor to drop the voltage to zero at its end. So at the drain of the Mosfet we have the inverted signal at whatever voltage is provided to the FET over the 100k resistor. This inverted signal can be used over a high resistance (eg 1M) to control the gate of an other MosFET, without to really affect the first mosFET.
Based on that I slapped together an 8 bit level shifter with generic MosFETs and it works just like in the simulation. That said, if it wasn't for that bag of 90 MosFETs type BUZ71 that I found for 2 bucks on a garage sale, I rather had used logic gates. To be on the save side, wire the signal through an AND gate that has a 4.5V supply, so the 3.3V would certainly seen as high. Then a second AND gate could be powered with 5V. These Chips are esp. useful as they have 4 Channels each. In case of AND and OR gates you just connect the signal to both inputs.
But anyway, if that MosFET IRG3708 works, great.
That is, from all I know, a common MosFet has already a Gate to Source drop of 1.5 to 2V, meaning you have 12V at the Drain, 3.3 at the Gate and end up with 1.8 V at the Source - barely enough to light up an LED.
However, you can use a MosFET in inverting mode, and then you can unleash all the 12Volts with a 3.3V signal, with most MosFETs.
Adding another MosFET inverts it back to normal.
There is a 100k ish resistor between VCC and the drain. Whenever the signal at the gate is low, no current can flow, hence Kirchhoffs law does not apply and we read 12 V between the drain and the 100k resistor. If the signal at the gate goes to 3.3 V, some current will flow from Drain to source, which causes the 100K resistor to drop the voltage to zero at its end. So at the drain of the Mosfet we have the inverted signal at whatever voltage is provided to the FET over the 100k resistor. This inverted signal can be used over a high resistance (eg 1M) to control the gate of an other MosFET, without to really affect the first mosFET.
Based on that I slapped together an 8 bit level shifter with generic MosFETs and it works just like in the simulation. That said, if it wasn't for that bag of 90 MosFETs type BUZ71 that I found for 2 bucks on a garage sale, I rather had used logic gates. To be on the save side, wire the signal through an AND gate that has a 4.5V supply, so the 3.3V would certainly seen as high. Then a second AND gate could be powered with 5V. These Chips are esp. useful as they have 4 Channels each. In case of AND and OR gates you just connect the signal to both inputs.
But anyway, if that MosFET IRG3708 works, great.
Statistics: Posted by dieter67 — Tue Feb 27, 2024 3:08 am