Principle Analysis of Series Negative Feedback Stabilized Power Supply
Circuit diagram of a series negative feedback regulator circuit, where T1 is the regulator, D1 and R2 form the reference voltage, T2 is the comparator amplifier, R3-R5 form the sampling circuit, and R6 is the load. Assuming that for some reason the output voltage UO decreases, the T2 base voltage (UT2) O decreases proportionally through the sampling circuit of R3-R5. As the T2 emitter voltage (UT2) E is controlled by the voltage regulator D1 to remain constant, the T2 emitter junction voltage (UT2) BE will decrease. As a result, the T2 base current (IT2) B decreases, the T2 emitter current (IT2) E decreases accordingly, and the T2 transistor voltage drop (UT2) CE increases, causing its emitter voltage (UT2) C to rise. That is, the adjustment transistor T1 base voltage (UT1) B will rise, and the T1 transistor voltage drop (UT1) CE will decrease, causing the input voltage UI to be added more to the load. In this way, the output The voltage UO rises. This adjustment process can be represented using the following change relationship diagram:
UO ↓ → (UT2) O ↓ → UD1 constant → (UT2) BE ↓ → (IT2) B ↓ → (IT2) E ↓ → (UT2) CE ↑
→(UT2)C↑→(UT1)B↑→(UT1)CE↓→UO↑
When the output voltage increases, the entire process of change is completely opposite to the above, which will not be repeated here. It can be simply represented by the following figure:
UO ↑ → (UT2) O ↑ → UD1 constant → (UT2) BE ↑ → (IT2) B ↑ → (IT2) E ↑ → (UT2) CE ↓
→(UT2)C↓→(UT1)B↓→(UT1)CE↑→UO↓
Similar to a simple series stabilized power supply, when other situations such as input voltage UI or load occur, it will cause corresponding changes in output voltage UO, and the working principle can be explained using the process analyzed above.
In the entire voltage stabilization control process of the series negative feedback stabilized power supply, due to the addition of the comparative amplification circuit T2, the change in output voltage UO is amplified by T2 and then controlled to adjust the base of the transistor T1, thereby enhancing the voltage stabilization performance of the circuit. The larger the beta value of T2, the better the stability of the output voltage.
