Applications to increase output voltage (a)

There are many ways to increase the output voltage of a fixed voltage regulator , the more commonly used ones are the following. Connect a voltage regulator tube
    in series between the common terminal of the voltage regulator and ground . The voltage stabilization value of the voltage regulator tube can be selected according to the following formula : (Figure 7-17(a,))     vo= Vx+ Vz vz='vo - Vx     where: 玎——the required DC voltage stabilization value (V) ,;     vx-the rated value (v) of the integrated voltage regulator used;     V z-the voltage stabilization value of the voltage regulator tube that needs to be connected in series.     The diode VDi in the picture is used to protect the voltage regulator tube. During normal use, the voltage at terminal 2 is higher than terminal 3, and the diode is in a cut-off state. When the output voltage is lower than the regulated value of the voltage regulator tube vo for some reason, or the output is short-circuited, the voltage at terminal 3 of the voltage regulator will be higher than terminal 2. At this time, the diode VDi is turned on, and the voltage regulator 3- The two terminals form a forward path, which prevents the current from flowing back to the voltage regulator from the three terminals and causing device damage .     It should be pointed out that in this circuit, the working current of the voltage regulator tube, d, is the static working current of the voltage regulator . When the input voltage changes, d also changes accordingly, causing slight changes in the output voltage and affecting the voltage stabilization accuracy. In order to reduce the impact of ld on the voltage stabilization accuracy, the circuit in Figure (b) can be used. At this time, the working current of the voltage regulator tube is IRi+Rukun. When the input voltage changes, Rl is a constant. Compared with the circuit in Figure (a), the change in the operating current of the voltage regulator tube is reduced by a factor of 1, which greatly improves the voltage stabilization accuracy.