I am looking to turn off/on a 5v laser diode with an esp8266 micro controller.
The mcu's gpio pins can only take 3.3v.
A PNP, NPN and mosfet, among these three which will help me boost the voltage to 5v and how should it be connected?
Electronic – Use a Mosfet/PNP transistor to boost voltage for mcu pin
esp8266mosfet
Related Solutions
MOSFETs have an internal diode that conducts in the reverse direction thus you see battery voltage on the diode node: -
Note the diode above. There is usually a diode junction from both source and drain to the substrate in both P and N channel MOSFETs. Here's the P channel MOSFET: -
What usually happens is that the manufacturer connects the "body" terminal to the source terminal so that one of the diodes can never be forward biased and this leaves the other diode able to be forward biased only when drain rises higher than source (P channel MOSFET).
Well, I figured out a solution, though I'm not exactly sure if it's the right one just yet.
I swapped out the Microchip TC4427 MOSFET driver in the above schematic for a ON Semiconductor MC34152. I ordered a few units of both drivers a while back, during the planning phase of this project. I swapped the TC4427 for the MC34152 thinking there would be no difference in performance, but it turns out that the MC34152 has a different internal design that somehow works better in motor applications.
The difference maybe in the varied hysteresis between the two ICs. The TC4427 offers 300mV of hyteresis between the high and low thresholds on the input, while MC34152 offers 170mV of hyteresis. Also, the MC34152's datasheet explicitly details internal 30K ohm pulldown resistor on each input and 100k ohm pulldown resistors on each output. These may prevent the "latch up" behavior I was experiencing before on the TC4427.
Either way, it works as intended now at 7.5V 2A output from the power supply. Time to see if the same can handle 7.4V 30A from a LiPo battery.
Best Answer
The easiest way would be something like this:
simulate this circuit – Schematic created using CircuitLab
When selecting the MOSFET, make sure it is a 'logic level' MOSFET that can turn on fully with 3.3V gate to source, and handle the current the laser diode uses.
Note that I don't show any current limiting here. If the laser diode doesn't include that you will need to use a resistor in series.