What are the voltage reference types of the power adapter?

The voltage reference of the power adapter is divided according to the operating principle

(1) Parallel reference

Figure 2-56 shows the Shunt Reference. The parallel reference is in parallel with the load. The reference voltage Uref=Uin-

lf×Rs=Uin-(Iq+Il)×Rs, such reference keeps U stable by adjusting l when the input voltage Uin or the load current I is produced. The parallel reference has only two pins, the price is cheaper, and it is more suitable for the occasion of little change in load current; Disadvantages are relatively large power consumption, input voltage adjustment rate is not ideal, common parallel reference models are LM358,AD589 and so on.

The voltage reference of the 6V power supply adapter is divided by process technology

(2) series reference

The Series Referenee is shown in Figure 2-57. Series reference and load are in series, reference voltage Uref=Uin-lf×Rs=Uin-(Iq+Il)×Rs. Since lq is small and remains basically constant, when U. Or l changes, the series reference keeps U stable by adjusting the resistance value of internal R. Series reference usually has 3 pins, input, output differential pressure and l. It can be made small, so it is more suitable for battery powered occasions. Common series reference models are AD581, REF192, etc.

(1) Zener benchmark

The advantages of Zener Reference are low cost, small package and wide operating voltage range. Disadvantages are high power consumption, low initial accuracy, large temperature coefficient, input voltage adjustment rate is not good, when used according to the supply voltage and load current connected to a resistance to provide a certain current, in order to maintain the output voltage stability, Zener benchmark is usually used for not high requirements of the occasion, or used as a voltage cap.

(2) Buried Zener datum

The Buried Zener benchmark Reference) has high initial accuracy, small temperature coefficient and good long-term drift stability, low noise voltage, and overall performance is better than other types of reference, so it is often used in the system with 12 bits or higher resolution. Occulting Zina reference usually requires a supply voltage of more than 5V, and consumes several hundred microamperes of current, so the price is relatively expensive.

(3) Band gap reference

The initial accuracy, temperature coefficient, long-term drift, noise voltage and other performance indicators of Bandgap Reference have a wide coverage from low to high, which is more suitable for 8-10 bit precision systems. This type of reference has both the type designed for general purposes and the static current is as small as tens of microamperes. The lower input and output voltage difference surface is suitable for products in battery-powered occasions, because the surface has a wide application range. In summary, band gap reference performance is good, moderate price, is the highest cost performance voltage reference.

(4)XFET benchmark

XFET is a new type of voltage reference, its performance level is between the band gap and Zener reference, the static current is very small, can be used in 3V voltage system, and still can maintain good performance,XFET reference has three remarkable characteristics: first, under the same working current condition, its peak-to-peak noise voltage is usually several times lower than the band gap reference; Second, the XFET reference has a very flat or linear temperature coefficient curve in the industrial temperature range, while the band gap and Zener reference temperature coefficient curve is often nonlinear at both ends of the temperature range, which is not easy to be corrected by software. Third, the XFET reference has excellent long-term drift stability.