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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 can be attributed to several main factors:
1. The input voltage (mains) is often unstable, as AC grids typically allow for a ±10% fluctuation. This causes the DC voltage from the rectifier and filter circuit to vary.
2. When the load RL changes (i.e., when the load current IL changes), the output DC voltage also changes due to the internal resistance of the rectification and filtering circuit.
3. Changes in ambient temperature can affect the parameters of circuit components, especially semiconductor devices, leading to variations in the output voltage.
Therefore, it is necessary to implement voltage regulation measures after the rectified and filtered DC voltage has been produced in order to meet the requirements of electronic equipment. Commonly used voltage regulator circuits are either shunt or series type.
Figure Z0717 shows a silicon voltage regulator circuit. Since the voltage regulator component DZ is connected in parallel with the load, it is referred to as a shunt regulator circuit. In this diagram, the input voltage Ui comes from the output of the rectifying and filtering circuit. R serves as both a current-limiting resistor and a voltage-regulating resistor, while UL represents the regulated voltage of the Zener diode DZ. 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/filter circuit (Ui) rises. This increase causes the output voltage UL (i.e., UZ) to rise. According to the voltage regulation characteristics of the Zener diode, this rise in UZ leads to a significant increase in IZ. As a result, the current I through resistor R increases, causing a larger voltage drop across R. This effectively counteracts the change in Ui, keeping UL essentially stable (Ui↑ → UL↑ → IZ↑ → I↑ → UR↑ → UL↓). Conversely, when Ui decreases and UL drops, IZ also decreases, reducing the voltage drop across R and maintaining the stability of UL.
Similarly, if the load current IL changes (i.e., RL changes), such as an increase in IL, and assuming Ui remains constant, this will cause UL (i.e., UZ) to decrease. This drop in UZ results in a large reduction in IZ, ensuring that the total current I (I = IZ + IL) remains approximately constant, which keeps UL stable.
From the above analysis, it's clear that the Zener diode plays a key role in controlling the current within the circuit. Even small fluctuations in the output voltage 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 the variation in IL, ensuring that UL remains largely unchanged.
Resistor R is essential in the circuit, acting as both a current limiter and a voltage regulator. If R were zero, the full input voltage Ui (which is much higher than UZ) would be directly applied across DZ, causing excessive IZ and potentially damaging the Zener diode. Additionally, without R, UL would simply equal Ui, and the circuit would lose its ability to regulate voltage. Therefore, the voltage regulation in this circuit is achieved through the combination of the Zener diode DZ and the current-limiting resistor R.