Schmidt trigger implemented by software

In some smart chargers, the single-chip microcomputer must constantly monitor the battery voltage. Once a value is exceeded, the constant current charging will switch to the constant voltage charging. Aside from the knowledge and concepts related to charger creation, let's focus on some things that happen when the voltage is close to that set critical value.

When the voltage is close to the critical value, the system is still in the constant current charging status, so the voltage begins to rise in the direction of breaking through the critical value ...... At a certain time point, the voltage broke through the critical value. The program detected this change and immediately switched the charging status from constant current to constant voltage. However, because the voltage loaded on the battery is much higher than the voltage maintained during constant current, the voltage is almost the same moment, the battery voltage detected by the Microcontroller has jumped back to the below critical value-so the system has simply switched the working mode back to the constant current status ...... This happens many times frequently when the battery voltage is near the critical value until the constant voltage is switched completely.

The above is what is supposed to happen from a micro perspective. The actual situation may be more complicated. However, from a macro perspective, the possible phenomenon is that the indicator lights in the charging mode of the charger flash alternately frequently-this is not what we need.

 

Is there any way to avoid this headache? It is easy to say that the critical voltage value for switching the working mode is changed from one to the two upper and lower thresholds. Switching from a constant current to a constant current requires a high threshold. This "high" is relative to a single threshold value. switching from a constant current to a constant current status requires a high threshold, the actual voltage must be lower than a value lower than the original single door limit-the difference between the high and low thresholds must be at least greater than the typical size of the front and back voltage difference caused by switching between two Charging Modes ". The trigger feature for changing the charging status of the charger is called the Schmidt feature. Using software to trigger this double threshold is called the "software Schmidt trigger ".

 
The main points of writing the "software Schmidt trigger" are to clarify the "two states" and "two limits ". The "two states" indicates which of the two States is in the current state. The current number is becoming larger or smaller, which is both random and local, and cannot be used as a basis for determining the current status. The only one that is qualified to determine the current status is the last status. The next monitoring object is determined based on the current status of the record. This is the most reliable method. For example, if we are in a constant voltage state, now we need to monitor the lower threshold. Once the voltage falls below the lower threshold, our current state changes to a constant current state. Therefore, we only need to stick to the upper threshold. The "two limits" mentioned here are the upper and lower two thresholds.