I'm designing a heater controller that has a primary input voltage between 12 and 24V. Everything except the heater runs on 3V3, including microcontroller, LED's, potentiometers and the MOSFET.
The problem is the MOSFET wont be operating at it's full potential, http://www.onsemi.com/pub_link/Collateral/NTD5406N-D.PDF Figure 2 shows that 3V3 limits the current to about 5-6 Amps. I need to switch up to 8 Amps.
As a work around I've considered the following:
- Using a 5V Regulator with a Shutdown Pin (LP2951) not ideal for PWM.
- Using a 5V Regulator a level shifter.
I'm planning to manufacture 1,000's so my goal is low parts count and reliable, cost is always a consideration but at around $0.50 (either of the above solutions) isn't too expensive.
Since I don't need much current (<1mA) and I only need a little more voltage (<4V total) on the MOSFET could I safely use a Zener diode or a voltage reference? What would that circuit look like? The couple of attempts I made at simulating these types of circuits didn't work.
I created a simulation of what I think is Alex's answer could somebody verify my understanding? Simulation of Alex's Circuit If this would work in the "real world" I like it. Simple and doesn't require another Voltage Regulator. FYI: The Zener pictured is 5V1 and the Input ("L") is 3V3.