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Parallel silicon regulator tube voltage regulator circuit - News - Global IC Trade Starts Here Free Products
The DC voltage obtained after rectification and filtering is relatively smooth, but its stability is not very good. This instability is mainly due to the following factors:
1. The input voltage (mains) is not stable, as AC power grids typically allow a ±10% fluctuation. As a result, the DC voltage from the rectifier and filter circuit becomes unstable.
2. When the load resistance RL changes (i.e., when the load current IL varies), the output DC voltage changes because of the internal resistance of the rectifier and filter circuit.
3. Changes in ambient temperature can affect the parameters of circuit components, especially semiconductor devices, which can cause fluctuations in the output voltage.
Therefore, after rectification and filtering, it's necessary to implement voltage regulation measures to meet the requirements of electronic equipment. Commonly used voltage regulator circuits include two types: shunt regulators and series regulators.
Figure Z0717 shows a silicon voltage regulator circuit. Since the voltage regulator component DZ is connected in parallel with the load, this configuration is called a shunt regulator. In the diagram, the input voltage Ui comes from the rectified and filtered circuit. R serves as both a current-limiting resistor and a voltage-regulating resistor. The output voltage UL is equal to the Zener voltage UZ. The current through R is I = IZ + IL, and UL = UZ = Ui - IR. The Zener diode operates in reverse bias.
The principle of voltage regulation in this circuit is as follows: when the grid voltage increases, the output voltage of the rectifier and filter circuit (Ui) also rises. This rise causes the output voltage UL (UZ) to increase. According to the characteristics of the Zener diode, an increase in UZ leads to a significant increase in IZ. As a result, the current through R (I) increases, causing a larger voltage drop across R, which helps counteract the change in Ui, keeping UL mostly stable. Conversely, when Ui decreases, UL drops, leading to a reduction in IZ, which lowers the voltage drop across R and maintains the stability of UL.
Similarly, when the load current IL changes (e.g., increases), if Ui remains constant, UL (UZ) would decrease, causing a drop in IZ. However, the total current I (I = IZ + IL) remains roughly constant, ensuring that UL stays stable.
From the above analysis, it’s clear that the Zener diode plays a key role in controlling current within the circuit. Even small fluctuations in UL caused by changes in Ui or IL lead to significant changes in IZ. These changes either adjust the voltage drop across R or compensate for variations in IL, ensuring that UL remains essentially constant. The resistor R acts as both a current limiter and a voltage regulator. If R were zero, the full Ui (which is much higher than UZ) would be applied directly across the Zener diode, causing excessive IZ and potentially damaging the diode. Additionally, without R, UL would simply equal Ui, and the circuit would lose its voltage regulation capability. Therefore, the voltage regulation in this circuit is achieved through the combination of the Zener diode DZ and the current-limiting resistor R.