24V-48V battery input auxiliary power circuit
In the inverter with input voltage above 24V, if the linear step-down such as L7812 and LM317 will cause relatively large heat loss, I designed a self-excited switching step-down circuit, which is introduced to everyone:
In this circuit, the BT input voltage range can reach 15-60V, and the output is stable at 12V. Q6 can also use P-type MOS transistors.
Let's talk about the working principle of this circuit. At the moment of circuit startup, the power supply provides a sufficiently large base current of Q6 through R13. Q6 is saturated and turned on. Part of the collector current is charged to C15 through L1, and part of it is stored in L1. . When the voltage across C15 exceeds 15V, Q7 turns on, and Q5 turns on, causing the base potential of Q6 to rise, the current to decrease, and the potential of the upper end of C11 to drop. Since the voltage across C11 cannot be abruptly changed, the potential of Q5 base continues to rise rapidly. When falling, the base potential of Q6 rises rapidly until it is turned off quickly. After Q6 is turned off, the energy storage of L1 is released to C15 and the load through the freewheeling diode D2, and then the cycle of the next cycle begins.
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