I agree a series resistor would prevent the GPIO conflict. The GPIO pin is necessarily configured as push-pull. A series resistor would reduce the efficiency of the buck converter. However my feeling is that if the resistor was small, say 220 ohms, it would suffice to resolve the fight and not significantly impact the efficiency.?
Gunnar, I'd like to understand why you're so sure the current through the zener and base-emitter is low? I agree as soon as the voltage rises it will stop the PWM and thus further energy being delivered into the inductor. My point is by this time significant additional energy was already delivered into the inductor which at 330uH, isn't tiny. Before the voltage rise could be detected and switch off the PWM. The energy will be dissipated through the zener and base-emitter. So my question is how are we so sure that it is "quite low", not a current spike which can kill the base-emitter junction? I'm just nervous because in my experience dumping even small energy into transistors via the base, was a quick death...
On Sun, Sep 3, 2023, 3:03 PM Evan Hand <elhandjr@...> wrote:
Hans,
Is it possible to set an interrupt routine based on time to sample the 5-volt input and shut down the output when it reaches a threshold value greater than 5 volts but less than the 5.6-volt zener voltage?? If the timing of the power loop is 1 ms, the fast interrupt loop would need to be on the order of 0.25 ms to be effective.? This would be a very short routine to sample and shut down only.? I have used this concept in industrial control systems to handle alarm conditions with insufficient processor capability to run the entire program within the required time.?
An alternative is to store the value of the input voltage and turn off the PWM signal until the voltage stabilizes for several slower control loop cycles.
There are many strategies possible with the fast timed interrupt loop.??The A-to-D conversion times do come into play.? For the control situation, a direct read capability bypassed normal I/O processing.
