2018-09-13
2018-09-13
I have been playing with the PIC24 which will be the basis for the serial and power board. Side track: need a catchier name for the serial and power board. SPB? S and PB? SaPB? VSPB? Vic’s SPB? Executive decision made: VSPB – Vic’s Serial and Power Board. Boom. Done.
I have been playing with the PIC24 which will be the basis for the VSPB. I don’t know if I like Microchip PICs because they’re good or I think that they’re good and like them because that’s the only thing I know? I choose to believe that it’s the former. Anywho, the PWM output is functional. The debug and configuration serial port is functional. Lots of LEDs have been added. I used a PWM module to implement a fade in/fade out heartbeat LED. I also added four LEDs that cycle back and forth like Kit from Night Rider. Why? Because; I had spare pins so I used them.
Here’s a quick potato shot of the breadboard in progress.
A notable change from the initial design rough-draft is the current control method (detailed here). Initially I was planning on PWMing the photovoltaic isolator in a closed feedback loop in order to vary the VGS thus keeping the FET in the active region. But then I decided to just PWM the current limiting FET directly. The direct drive method is simpler and more conducive to a microcontroller application, in my opinion. The gate driver I will be using is a Microchip TC4432EOA. I spent a bit of time studying FET drive methods and decided it’s best to leave it to the specialists. The research went into the weeds exceptionally fast. You really can’t beat the value you get for the price of a single TC4432EOA.
The drive FET has been changed to Nexperia PHP29N08T. Primary change is due to max VGS. Since I’ll be using a gate driver, I will be applying the full 24VDC rail voltage to the gate rather than tickling it with a photovoltaic isolator.
That’s it for now. The FETs and the gate drivers are slated to be delivered from Mouser tomorrow. Once they get here they will be thoroughly abused and the results posted.