Circuit and Project Series Commutated SCR SSS Solar Charge Control using S2800A

Solar. - Here is Circuit and Project Series Commutated SCR SSS Solar Charge Control using S2800A. A series commutated SCR makes a very unusual Solid State Switch in this solar charge regulator control. Advantages include simplicity and robustness. The SCR performs (3) functions: switch, latch and reverse polarity diode (reverse blocking thyristor). The SCR conducts the charging current from the solar panel to the battery while a series MOSFET performs the function of commutating (turning off) the SCR current at the end of the conduction period. All circuitry consists of readily available discrete components.

The SCR has its gate driven by a PUT (Programmable Unijunction Transistor) gate driver. The advantage is high gate drive current (100mA peak), fast pulse rise-time and Schmitt Trigger type of operation. Q1 is wired as a free-running oscillator that outputs pulses every 6seconds (0.1HZ). Resistors R3 & R4 bias the gate of the PUT at mid voltage. When C1 charges to one junction drop above the gate voltage, it fires and the charge in C1 is dumped into the SCR gate. R5 limits the peak current and extends the pulse duration. When the PUT anode voltage drops below the threshold current, the PUT turns off and the cycle repeats.

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