Rectification | 整流 - aleveler.com

📚 Rectification | 整流

Rectification is the process of converting an alternating current (a.c.) into a direct current (d.c.). A rectifier circuit allows current to flow in only one direction through a load, so the alternating input becomes a unidirectional output. In CIE A-Level Physics, rectification is studied as a key application of the PN junction diode, together with half-wave rectification, full-wave rectification, bridge rectifiers, and capacitor smoothing.

整流是把交流电转换为直流电的过程。整流电路只允许电流沿一个方向流过负载，因此交变的输入会变成单向输出。在 CIE A-Level 物理中，整流作为 PN 结二极管的一项关键应用来学习，内容包括半波整流、全波整流、桥式整流以及电容滤波。

1. What Is Rectification? | 什么是整流？

Alternating current reverses direction periodically, so its average value over a full cycle can be zero. Many electronic devices, such as radios, chargers, and computer circuits, require a steady direct current with a fixed polarity. Rectification is therefore the first stage in most d.c. power supplies.

交流电会周期性地改变方向，因此一个完整周期内的平均值可以为零。许多电子设备，如收音机、充电器和计算机电路，都需要极性固定的稳定直流电。因此，整流是大多数直流电源中的第一级处理。

A rectifier makes use of a diode, which has a very low resistance when forward biased and a very high resistance when reverse biased. If an a.c. supply is connected through a diode to a load, current can pass only during the half cycles in which the diode is forward biased. The resulting current always flows through the load in the same direction.

整流器利用二极管，二极管正向偏置时电阻非常低，反向偏置时电阻非常高。如果交流电源通过二极管连接到负载，那么只有在二极管正向偏置的半周期内，电流才能通过。这样负载中得到的电流总是沿同一方向流动。

2. The PN Junction Diode as a Rectifier | PN 结二极管作为整流器

A silicon diode conducts when its anode is positive with respect to its cathode. In practice, a small forward voltage of about 0.7 V is needed before significant current flows. When the polarity reverses, the depletion region widens and the diode blocks almost all current, acting like an open switch.

硅二极管在其阳极相对于阴极为正时导通。实际上，需要有大约 0.7 V 的正向电压，才会有明显电流通过。当极性反过来时，耗尽区变宽，二极管几乎阻断所有电流，相当于一个断开的开关。

In an a.c. circuit, the diode is automatically forward biased during one half of the input cycle and reverse biased during the other half. This switching action is what makes the diode suitable for rectification. The symbol for a diode is a triangle pointing from the anode toward the cathode, indicating the direction of conventional current flow when the diode conducts.

在交流电路中，二极管会在输入周期的半个周期内自动正向偏置，在另外半个周期内反向偏置。这种开关作用使二极管适合用于整流。二极管的符号是一个从阳极指向阴极的三角形，表示二极管导通时常规电流的方向。

3. Half-Wave Rectification | 半波整流

A half-wave rectifier consists of a single diode connected in series with the load resistor. During the positive half cycle of the input, the diode is forward biased, so it conducts and a voltage appears across the load. During the negative half cycle, the diode is reverse biased, so it does not conduct and the output voltage is almost zero.

半波整流器由单个二极管与负载电阻串联组成。在输入的正半周期内，二极管正向偏置，因此导通，负载两端出现电压。在负半周期内，二极管反向偏置，因此不导通，输出电压几乎为零。

If the input is a sinusoidal voltage with peak value V_p, the peak output voltage is approximately V_p − 0.7 V for a silicon diode. The output is a series of positive pulses separated by gaps, so the average d.c. output is much lower than the peak value.

如果输入是峰值为 V_p 的正弦电压，对于硅二极管，输出峰值电压约为 V_p − 0.7 V。输出是一系列正脉冲，中间有间隙，因此平均直流输出远低于峰值。

4. Half-Wave Output and Ripple | 半波输出与纹波

The output of a half-wave rectifier is a pulsating direct current. It is unidirectional, but its magnitude is not constant. The output waveform has the same frequency as the input a.c. because only one pulse is produced per input cycle.

半波整流器的输出是脉动直流电。它是单向的，但大小并不恒定。输出波形的频率与输入交流电相同，因为每个输入周期只产生一个脉冲。

The variation in output voltage is called ripple. For half-wave rectification, the ripple frequency equals the supply frequency, f. For example, a 50 Hz mains input produces a ripple frequency of 50 Hz. This large ripple makes unsmoothed half-wave rectification unsuitable for most sensitive electronic circuits.

输出电压的波动称为纹波。对于半波整流，纹波频率等于电源频率 f。例如，50 Hz 的市电输入会产生 50 Hz 的纹波频率。这种较大的纹波使得未滤波的半波整流不适合大多数灵敏电子电路。

5. Full-Wave Rectification Using a Centre-Tap Transformer | 使用中心抽头变压器的全波整流

A full-wave rectifier produces an output pulse during both half cycles of the input. One method uses a transformer with a centre-tapped secondary winding and two diodes. The centre tap acts as the common reference point for the load.

全波整流器在输入的两个半周期内都产生输出脉冲。一种方法是使用带有中心抽头次级绕组的变压器和两个二极管。中心抽头作为负载的公共参考点。

During one half cycle, the top end of the secondary is positive with respect to the centre tap, so diode D₁ conducts while D₂ is reverse biased. During the other half cycle, the bottom end is positive, so D₂ conducts while D₁ is reverse biased. The load receives current in the same direction in both half cycles.

在一个半周期内，次级线圈的上端相对于中心抽头为正，因此二极管 D₁ 导通，而 D₂ 反向偏置。在另一个半周期内，下端为正，因此 D₂ 导通，而 D₁ 反向偏置。负载在两个半周期内都得到相同方向的电流。

The centre-tap full-wave rectifier uses two diodes, but it requires a special transformer with a centre-tapped secondary. Each half of the secondary winding supplies only half the total secondary voltage, so the peak output voltage is about half the peak voltage of one complete secondary winding minus the diode forward drop.

中心抽头全波整流器使用两个二极管，但需要一个带中心抽头次级绕组的特殊变压器。次级绕组的每一半只提供总次级电压的一半，因此输出峰值电压约为整个次级绕组峰值电压的一半再减去二极管正向压降。

6. Full-Wave Bridge Rectifier | 全波桥式整流器

The bridge rectifier uses four diodes arranged in a closed loop. It does not require a centre-tapped transformer. The a.c. input is applied across one diagonal of the bridge, and the load is connected across the other diagonal.

桥式整流器使用四个二极管组成闭合环路。它不需要中心抽头变压器。交流输入加在桥的一个对角线上，负载连接在另一个对角线上。

During the positive half cycle, two diodes conduct and direct current through the load in one direction. During the negative half cycle, the other two diodes conduct, but the current through the load still flows in the same direction. The load therefore receives a full-wave rectified output.

在正半周期内，有两个二极管导通，使电流以一个方向流过负载。在负半周期内，另外两个二极管导通，但流过负载的电流方向仍然相同。因此，负载得到全波整流输出。

The bridge rectifier makes better use of the secondary voltage than a centre-tap circuit because the whole secondary winding supplies the load on each half cycle. Its main disadvantage is that it requires four diodes, and current must pass through two diodes in series, giving a total forward voltage drop of about 1.4 V for silicon diodes.

桥式整流器比中心抽头电路更充分地利用次级电压，因为整个次级绕组在每个半周期都向负载供电。其主要缺点是需要四个二极管，而且电流必须经过两个串联的二极管，硅二极管的总正向压降约为 1.4 V。

7. Comparing Half-Wave and Full-Wave Rectification | 半波与全波整流比较

Both half-wave and full-wave rectifiers convert a.c. into pulsating d.c., but their output waveforms and efficiency are different. Full-wave rectification uses both halves of the input cycle, so it produces a higher average output voltage and a smaller ripple than half-wave rectification.

半波和全波整流器都能把交流电转换为脉动直流电，但它们的输出波形和效率不同。全波整流利用了输入周期的两个半周期，因此它产生的平均输出电压更高，纹波比半波整流更小。

Feature 特征	Half-Wave 半波	Full-Wave 全波
Number of diodes 二极管数量	1	2 or 4
Output pulses per cycle 每周期输出脉冲数	1	2
Ripple frequency 纹波频率	f	2f
Average output voltage 平均输出电压	Lower 较低	Higher 较高
Transformer requirement 变压器要求	Ordinary 普通	Centre-tap or bridge 中心抽头或桥式

The table above summarises the main differences. In general, full-wave rectification is preferred in practical power supplies because it is more efficient and easier to smooth.

上表总结了主要区别。一般来说，实用电源更倾向于采用全波整流，因为它效率更高，也更容易滤波。

8. Smoothing with a Capacitor | 电容滤波

The output of a rectifier is a pulsating d.c. that is unsuitable for many circuits. A capacitor connected in parallel with the load can smooth the output by storing charge when the rectified voltage rises and releasing charge when it falls.

整流器的输出是脉动直流电，不适合许多电路使用。与负载并联的电容器可以在整流电压升高时储存电荷，在电压下降时释放电荷，从而对输出进行滤波。

When the rectified voltage increases, the capacitor charges up to nearly the peak voltage. When the rectified voltage falls, the capacitor discharges through the load, maintaining a current and preventing the output voltage from falling to zero. The output becomes a smoother d.c. voltage with a small sawtooth ripple.

当整流电压升高时，电容器充电至接近峰值电压。当整流电压下降时，电容器通过负载放电，维持电流并防止输出电压降到零。输出就变成了较平滑的直流电压，带有较小的锯齿形纹波。

9. Ripple and Time Constant | 纹波与时间常数

The amount of smoothing depends on the time constant of the capacitor-resistor combination. The time constant τ is the product of the load resistance and the capacitance:

滤波程度取决于电容器-电阻器组合的时间常数。时间常数 τ 是负载电阻与电容的乘积：

τ = Rₗ C

A larger time constant means that the capacitor discharges more slowly between input peaks, so the output voltage falls less and the ripple is smaller. To improve smoothing, either the capacitance C or the load resistance Rₗ must be increased.

时间常数越大，电容器在输入峰值之间放电越慢，因此输出电压下降越少，纹波越小。要改善滤波效果，可以增大电容 C 或增大负载电阻 Rₗ。

For a full-wave rectified supply, the approximate peak-to-peak ripple voltage can be estimated using:

对于全波整流电源，近似的峰峰值纹波电压可以用下式估算：

V_ripple ≈ Iₗ / (2 f C)

where Iₗ is the load current, f is the supply frequency, and C is the smoothing capacitance. For half-wave rectification, the factor 2 is replaced by 1, giving a larger ripple for the same values.

其中 Iₗ 是负载电流，f 是电源频率，C 是滤波电容。对于半波整流，分母中的 2 应改为 1，因此在相同参数下纹波更大。

10. Load Resistance and Ripple | 负载电阻与纹波

When the load resistance is large, the load current is small, so the capacitor discharges slowly and the ripple voltage is small. However, a large load resistance also means that the supply delivers less current to the load.

当负载电阻较大时，负载电流较小，电容器放电缓慢，纹波电压就小。然而，负载电阻大也意味着电源向负载提供的电流较小。

If the load resistance is reduced, the load current increases, the capacitor discharges more quickly, and the ripple becomes larger. In practical power supplies, the smoothing capacitor must be large enough to keep the ripple within an acceptable range for the expected load current.

如果负载电阻减小，负载电流增大，电容器放电更快，纹波就变大。在实际电源中，滤波电容必须足够大，以便在预期的负载电流下把纹波控制在可接受范围内。

This is an important design trade-off: increasing C reduces ripple but also increases the surge current when the supply is first switched on. Large capacitors also store more energy, which can be dangerous if the circuit is not handled correctly.

这是一个重要的设计权衡：增大 C 可以减小纹波，但也会增加电源刚接通时的浪涌电流。大电容还会储存更多能量，如果处理不当可能造成危险。

11. Practical Rectifier Circuits and Diode Ratings | 实际整流电路与二极管额定值

In a practical rectifier, each diode must be able to withstand the maximum reverse voltage that appears across it. The peak inverse voltage, or PIV, is the largest reverse voltage a diode experiences during the cycle without breaking down.

在实际整流器中，每个二极管都必须能够承受它两端出现的最大反向电压。峰值反向电压（PIV）是二极管在周期内承受的最大反向电压，而不发生击穿。

For a half-wave rectifier, the PIV is approximately equal to the peak secondary voltage. For a centre-tap full-wave rectifier, each diode can experience a reverse voltage approximately equal to the whole secondary peak voltage. In a bridge rectifier, the PIV across each non-conducting diode is approximately the peak supply voltage minus one diode drop.

对于半波整流器，PIV 大约等于次级峰值电压。对于中心抽头全波整流器，每个二极管可能承受约等于整个次级峰值电压的反向电压。在桥式整流器中，每个不导通二极管两端的 PIV 大约等于电源峰值电压减去一个二极管压降。

Diodes must also have a current rating greater than the maximum load current. The smoothing capacitor must have a voltage rating greater than the peak output voltage, with a safety margin. In mains-powered circuits, a fuse and proper insulation are essential for safety.

二极管的额定电流还必须大于最大负载电流。滤波电容的额定电压必须大于输出峰值电压，并留有一定安全余量。在市电供电的电路中，保险丝和良好的绝缘对安全至关重要。

12. Exam Tips for CIE A-Level Physics | CIE A-Level 物理考试提示

When answering CIE A-Level Physics questions on rectification, you should be able to draw and recognise the circuits for half-wave, centre-tap full-wave, and bridge rectifiers. Label the diodes, load resistor, transformer, and smoothing capacitor clearly.

在回答 CIE A-Level 物理中关于整流的问题时，你应当能够画出并识别半波、中心抽头全波和桥式整流电路。要清楚地标出二极管、负载电阻、变压器和滤波电容。

Be prepared to explain how a diode conducts during one half cycle and blocks during the other, and why the load current remains unidirectional. Exam answers often ask for the ripple frequency of half-wave and full-wave outputs, so remember that full-wave ripple frequency is 2f.

要能够解释二极管如何在一个半周期导通、在另一个半周期截止，以及为什么负载电流保持单向。考试答案经常要求写出半波和全波输出的纹波频率，因此要记住全波纹波频率是 2f。

Draw circuit diagrams with a ruler and label every component. 用尺子画电路图，并标出每个元件。
Use arrows to show the conducting path during each half cycle. 用箭头表示每个半周期内的导电路径。
If a question asks about smoothing, mention charge and discharge of the capacitor. 如果题目问到滤波，要提到电容器的充电和放电。
Use the approximation V_ripple ≈ Iₗ / (2 f C) for full-wave smoothing when numerical values are given. 当给出数值时，全波滤波可使用近似式 V_ripple ≈ Iₗ / (2 f C)。

Finally, distinguish clearly between alternating current, pulsating direct current, and steady direct current. A rectifier alone gives pulsating d.c.; adding a capacitor gives smoother d.c.; additional regulation may be needed for a nearly constant d.c. output.

最后，要清楚地区分交流电、脉动直流电和稳定直流电。只用整流器得到的是脉动直流电；加上电容器后得到较平滑的直流电；若需要几乎恒定的直流输出，还可能需要进一步稳压。

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Rectification | 整流