In this article we analyze some important voltage regulator circuits using discrete components such as transistors, zener diodes, resistors etc. These regulators are highly flexible with their design specifications, and can be customized for generating any level of constant voltage and constant current, as desired.
What is a Regulator
直流调节电路的主要功能generate a voltage and current that is fixed and constant at a certain specified levels. Thus, a regulator is used in a power supply to keep the output voltage or current within certain fixed limits.
一个lso Recommended for you:Voltage Regulator Circuits using Transistor and Zener Diode
一个完美的电源会零内部再保险sistance (ideal voltage source) or indefinite internal resistance (ideal current source), causing the output voltage or current to be independent of load. These supplies would have to be able to produce endless quantities of power, and these would, obviously, simply exist in theory only.
When a really pure DC supply is required,linear regulatorsoften become useful since they produce lesser noise, ripple, and better control.这些监管机构通常是三端设备（输入，共同点和输出），因此只需要少数外部组件（流行的7800和7900系列调节器IC只需要几个0.01UF至1 UF的电容器，而只需要1 UF，而仅需要几个电容器在特定条件下。）
这些监管机构从字面上看，可以表现出远低于1％的法规，同时还提供了相当大的当前限制和整合故障预防功能。还有一些切换调节器和电压转换器IC，实际上需要很少的外部电容器，而无需其他。这些廉价的调节器和转换器使得为无法通过系统的主要电源提供的电压提供离散电路的可行性和简单。这种配置通常避免使用电源限制，从而允许更大的设计自由。
Simplest Regulator
最基本的调节器采用了两端设备，例如齐纳二极管，其特征是在其上保持恒定电压。下面的图1描述了基本电路。
齐纳二极管可以以任何配置串联连接，以实现更高的电压。一个current-limiting（镇流器）必须合并电阻，因为这些设备将通过从电源可用的任何电流来尝试保留恒定端子电压。
Efficiency is essential.
The regulating device's impedance might be quite low, and it could rapidly drain catastrophic quantities of current in the absence of a limiting resistor, and get damaged.
Therefore a limiting resistor becomes necessary for azener diode. Because the regulating component is shunted across the load, this type of zener circuit (Fig. 1) is often called a shunt-type regulator.
当只需要几毫安的电流，并且只需几个百分比的调节（在不同负载下的电压或电流）就足够了，因此该方法非常适合低功率应用。
Since the entire current flowing through the limiting resistor is the sum of the load current plus the regulator current required to maintain the voltage, efficiency is often poor, particularly at low loads.
High amounts of current is able to pass through the regulator when the load is disconnected or changed. While this is not an issue for tiny circuits such as an oscillator circuit that draws only a few milliamperes, it can be an issue in a circuit like a tiny digital device that might require around 1 amp at 5 volts.
In some circumstances (LED lights, on-off switches), the system may use less than 50 milliamps in standby mode and 1 amp in active mode. A zener-diode regulator would be highly ineffective in such cases as it will have to pass roughly 1 amp through the zener while the system were idle and therefore not consuming its operational current.
In such scenario if the input voltage was 12 volts, the efficiency of the 12V to 5V regulator might be extremely low due to the presence of a constant load of above 1 amp on the 12 volt supply, even if the load on the 5 volt supply side was small.
This equates to 12 watts or even more heat creation, which is an extremely inefficient condition.
一个n easy remedy is to employ an主动调节器which might not demand so much current to operate.
It should be noted, however, that there will always be some voltage loss across the regulator. Because the regulator circuit is an amplifier, it will itself require some voltage to function.
The pass transistor's base-emitter voltage is 0.6 to 0.7 volts, and there will be some voltage loss in the bias resistors. The input voltage must be consistently at least 2 to 5 volts higher than the highest anticipated output voltage; it must never go below this level or else the output control will be affected.
This minimum voltage must always be maintained under minimal-input-line-voltage situations at full load. Below this threshold, instantaneous changes owing to input-supply ripple, load transients, and so on will result in a loss of regulation ( "drop-out ").
使用晶体管发射器跟随器的调节器
In Fig. 2 below, anemitter follower晶体管用于最小化调节器设备所使用的电流。Zener二极管接收10或20 mA。该电压应用于晶体管的底部，该电压称为"pass" transistorsince it is positioned to pass the load current.
This could be ahigh-power transistorrated to handle many amps of current.
The load current is made up of the collector current, which makes up the bulk of the current, and the base current. The base current is equal to the collector current divided by the transistor's DC gain (or beta, which is normally equal to 50).
一个ssuming the transistor has a current gain β of 50 and a load current of 1 amp, the collector current can be calculated as given below
收集器电流=β/（β+1）= 1安培或50/51安培。
Base current can be calculated using the following formula:
碱电流= 1 /（β+1）或1/51 amp。
This is somewhat less than 20 milliamperes. Figure 2 above depicts the basic regulator design.
Using a Darlington with Pass Transistor
Figure 3 below illustrates how an auxiliary transistor could be used as an intermediate stage if the pass transistor happens to be a very high current, low hFE device.
The intermediate transistor is configured as aDarlington pairwith the pass transistor significantly increase its current gain and also enhance its current transfer ability.
It should be noted that when there is no load, the only current consumed by the circuit is that of the zener diode only.
Creating an Adjustable Regulator
也可以在整个齐纳二极管上连接可变电阻器或锅，如果将锅的雨刮器连接到晶体管的底部，则可以实现如下图4所示的可变输出电压。
The issue with this circuit is that it is no better (in fact, somewhat worse) than a zener diode as a regulator. There is no system in place to ensure that the output voltage to the load remains constant.
此外，通过晶体管中的基本发射极下降会导致输出电压降低（通常为每晶体管0.6至0.7伏）。如果使用电位计用于更换输出电压，则可能由于锅电阻而发现额外的损失。
This resistance results in a decrease in regulation. The regulator has no way of knowing if the output voltage has dropped. What's truly needed is a means to sense the output voltage, compare it to a set reference, and change the output voltage to the appropriate value automatically.
This necessitates the use of a feedback mechanism to regulate the output voltage. With a few more elements, we'll show you a really simple approach to achieve this.
Regulator with Feedback for Enhancing Output Accuracy
Figure 5 below depicts a very basic feedback regulator wherein the output voltage has some control over its exact level. R1 and R2 form a voltage divider that samples the output voltage and sends it to transistor Q1's base.
The drop across zener diode D1 holds the emitter of Q1 at a set and regulated voltage. The bias current from R3 and the emitter current from Q1 cause this dip.
该下降是由R3的偏置电流和Q1的发射器电流生成的。
If the output voltage drops, Q1 would be switched off, allowing less current to flow via bias resistor R4. The collector voltage will increase, enhancing the voltage at the base of pass transistor Q2 and, hence, the emitter of Q2, that tends to be the power supply regulator's output terminal.
This voltage increase will be sent to the base of Q1, compensating for the original dip. The total impact will result in an increased output voltage stability.
100% Perfection is not Possible
This adjustment, however, is not the ideal one. The regulator circuit is a limited gain feedback amplifier. Because the voltage gain is mostly provided by Q1, the circuit could have a net open-loop voltage gain of may be around 20-100, depending on Q1 gain, power supply load, zener diode impedance, and other parameters. Loop gain can be defined as the product of total gain multiplied by the feedback factor.
在这种情况下，反馈因子是R2 /（R1 + R2）的比率。其他一切都相等，循环收益越大，监管越好。实际上，与早期电路相比，该电路将提供10倍或更高的调节增强。但是，他的电路有一定的限制，其中一些如下：
- 在Q1中，输出电压不能低于齐纳电压 +基本发射极损耗。
- There is no current limiting or short-circuit protection. Since there will always be a voltage loss across R4, the maximum regulated output voltage is restricted.
- Because the feedback factor R2 /(R1 + R2) declines with increasing output voltage, regulation becomes gradually worse.
- Because part of the bias currents (via R3 and R4) originate from the unregulated side, the output would be impacted by fluctuations in the input voltage, worsening regulation.
These issues could be resolved with circuit adjustments and with the installation of a few additional components. The first problem can be solved by using a low voltage zener diode, even though the best reliable zeners are approximately 5 to 8 volts.
It is feasible to utilize a secondary floating power supply circuit to deliver voltages below (negative) ground and transfer R2 to a negative voltage rather than ground.
Connect a resistance to the input, and the voltage drop across it can work as a function of load current which can influence the regulator output. Extra open-loop gain could be obtained by using additional transistors or an op-amp.
当前限制
下面的图6描述了合并电流限制的一种方法。电阻R4与PNP晶体管Q1串联连接，该晶体管用作电流源。
This resistor is required to restrict the current sent to D1. At the base of Q1, diodes D2 and D3 generate a very constant voltage which is 1.4 volts lower than the regulator input voltage.
Q1进行只要the voltage drop caused by the pass -transistor collector current is less than around 0.7 volts across sampling resistor R5. As the load current builds, the drop over R5 rises to the extent where it begins to cut off Q1.
R4现在可以迫使通过晶体管Q2的基本电压下降，从而导致调节器输出电压降低。由于该电流还偏向参考齐纳二极管D1，因此参考电压下降，降低输出电压。因此，从监管机构中获取的电流可能受到这种方式受到限制。
一个0.7 volt drop across R5 will initiate current limiting, hence R5 should have a value of 0.7 /(Current Limit), or around 0.7 ohms for 1 amp, 0.35 ohms for 2 amps, and so on.
Using an Op Amp
下面的图7显示了如何引入运算放大以增强控制。请注意，收益现在将大幅度增加。然而，在某些情况下，几乎可以肯定需要频率校正，因为在负载的某些或所有阶段，循环相移可能会产生振荡。
尽管可以直接从调节器提供操作AMP的偏置，但通常需要额外的辅助低功率供应。
一个negative source may be required for the op-amp, particularly in case the regulator is intended to be adjustable or to swing down to zero volts output, as in alaboratory power supply.
This concludes our article on simple voltage regulator circuits. If you have any queries or modifications related to the above concepts please feel free to comment below for quick replies.
