Proceeding, we recall that across the inductor an inductive voltage 
(3)
where 
This action of the inductor seems dual to the case of the capacitor wherein capacitor current 
(4)
In addition, D1’s action similar to that of D2 is inhibited by the presence of diode D3 at the collector of Q1. This diode at the collector of Q1 prevents the gate terminal of the SCR1 from rendered at 0 potential whenever diode D1 conducts at range of battery voltages equal to or greater than its Zener voltage (plus the voltage drops mentioned earlier). The conduction of D1 in effect turns the collector of Q1 low (at 0 potential with respect to ground) but this zero potential at the collector cannot ground the SCR1 gate since this gate sees a reverse diode D3 that can be approximately represented by an infinitely high impedance ZD3. So SCR1 can continue conducting from its initial conducting state irrespective of the conducting state of D1 and the SCR1 is triggered off only when D2 conducts so as to render the collector of Q2 at zero potential (low) at range of battery voltages equal to or greater than D2 Zener voltage (plus the voltage drops earlier mentioned). The non-conducting state of SCR1 at this another instant can continue until it is triggered back on when the collector of Q1 goes high as D1 and Q1 turn off at those voltages below D1’s Zener voltage (plus the voltage drops of connected circuit elements). Note here that Q1’s collector side sees a forward diode D3 (with approximately zero-value impedance ZD3) and so in this ideal approximation this diode acts as a closed switch that connects the gate of SCR1 to the collector node of Q1 where this gate sees a positive triggering voltage VCC thus, turning SCR1 on provided that D2 and Q2 are also off. Also note here transistors Q1 and Q2 are biased in such a way that they will be at saturation to put their respective collectors at zero potential whenever they are conducting.
The miniaturized setup is as illustrated in the block diagram.
In the setup, the heart of the system is the automatic solar low voltage shutdown (aslvs) module that controls the flow of supply voltage coming from the solar panel to a recharging load.
This module senses the voltage output of the solar panel that automatically establishes the connection between the solar panel and the load when the solar panel output voltage is sufficiently above the designed (set) threshold level, otherwise disconnects the panel when such output is below the set level.
As an alternative setup for the aslvs module we can replace the relays (Relay1, Relay2) with a power e-mosfet (Q4) that acts as a power switch that is controlled by the aslvs masterboard as shown below.
Green LED with its biasing resistor R6 is optional.
The aslvs module is in turn controlled by the feedback and control section
that acts as the charge controller (autoshutoff/on) whose function is to detect the charging voltage level of the battery and at the instant when the battery voltage reaches a designed full charged level, this section automatically commands the aslvs to disconnect the solar panel. On the other hand, the feedback and control section will also detect the discharged voltage level of the battery and will command the aslvs section to re-establish connection to the solar panel when the battery terminal voltage has reached a designed discharged level.
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