Voltage divider circuits can be designed using operational amplifiers (op-amps) and bipolar junction transistors (BJTs), especially when the load is variable or not symmetrical. In such cases, traditional voltage dividers may not perform optimally. To address this, a more advanced approach involves using a single op-amp (like TL071, OPA134, NE5534/A, or LM741) along with complementary BJTs (such as PN2222A + PN2907A, BD135 + BD136, etc.). This combination allows for better stability and performance in various applications.
Figure 5 illustrates an example of such a circuit. The output voltage is adjusted using a potentiometer P1. The gain of this voltage divider is given by Av = 1 + R4/R5. If R5 is not required, the gain can be set to 1, effectively making it a voltage follower. This design also functions as a current buffer, which helps in driving heavier loads without affecting the input signal.
The output current range of this circuit typically falls between 50mA and 2000mA, depending on the transistor capabilities and the op-amp used. A capacitor C4 is only added if external frequency compensation is necessary for the op-amp. Many audio power amplifiers already incorporate all the components shown in Figure 5, making them ideal for both adjustable and fixed voltage divider designs.
This type of circuit is particularly useful in situations where precision and adaptability are required. Whether you're working on a custom power supply, a signal conditioning module, or a low-noise amplifier, combining op-amps and BJTs offers a flexible and robust solution. Understanding how these components interact can greatly enhance your ability to design efficient and reliable electronic systems.
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