Principle analysis of series negative feedback regulated power supply
The circuit diagram of a series negative feedback voltage stabilizing circuit, where T1 is the adjustment transistor, D1 and R2 form the reference voltage, T2 is the comparison amplifier, R3-R5 forms 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 from R3 to R5. Since the T2 emitter voltage (UT2) E is controlled by the voltage stabilizing value of the regulator D1, the T2 emitter junction voltage (UT2) BE will decrease, resulting in a decrease in T2 base current (IT2) B, a decrease in T2 emitter current (IT2) E, and an increase in T2 transistor voltage drop (UT2) CE, Causing an increase in emitter voltage (UT2) C, i.e. adjusting the base voltage (UT1) B of transistor T1 will increase, while the voltage drop (UT1) CE of transistor T1 will decrease, causing more input voltage UI to be applied to the load, resulting in an increase in output voltage UO. This adjustment process can be represented by the following change relationship:
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, so we will not repeat it here, but simply use the following diagram to represent it:
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 regulated power supply, when other conditions such as input voltage UI or load occur, it will cause corresponding changes in output voltage UO. The above analysis process can ultimately be used to explain its working principle.
In the entire voltage stabilization control process of the series negative feedback power supply, due to the addition of a comparative amplification circuit T2, the change in output voltage UO is amplified by T2 before controlling and adjusting the base of transistor T1, which enhances the voltage stabilization performance of the circuit. T2 β The larger the value, the better the stability of the output voltage.
