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Window Detectors The function of a window detector, also called a window comparator, is to indicate when a given voltage falls within a specified band, or window. This function is implemented with a pair of level detectors, whose thresholds VTL, and VTH define the lower and upper limits of the window. Referring to Fig. 9.13a, we observe that as long as VTL VTH. Q02 for v1 < VTL) and bring vo near 0 V. Figure 9.13b shows the resulting VTC. If Re is replaced by an LED in series with a suitable current-limiting resistor, the LED will glow whenever vi falls outside the window. If we wish the LED to glow whenever vi falls inside the window, then we must insert an inverting stage between the comparators and the LED-resistor combination. An inverter example is offered by the 2N2222 BJT of Fig. 9.14. The window detector shown monitors whether its own supply voltage is within tolerance. The top comparator pulls the base of the 2N2222 BJT low whenever Voc

Window Detectors The function of a window detector, also called a window comparator, is to indicate when a given voltage falls within a specified band, or window. This function is implemented with a pair of level detectors, whose thresholds VTL, and VTH define the lower and upper limits of the window. Referring to Fig. 9.13a, we observe that as long as VTL VTH. Q02 for v1 < VTL) and bring vo near 0 V. Figure 9.13b shows the resulting VTC. If Re is replaced by an LED in series with a suitable current-limiting resistor, the LED will glow whenever vi falls outside the window. If we wish the LED to glow whenever vi falls inside the window, then we must insert an inverting stage between the comparators and the LED-resistor combination. An inverter example is offered by the 2N2222 BJT of Fig. 9.14. The window detector shown monitors whether its own supply voltage is within tolerance. The top comparator pulls the base of the 2N2222 BJT low whenever Voc

Introductory Circuit Analysis (13th Edition)
Introductory Circuit Analysis (13th Edition)
13th Edition
ISBN:9780133923605
Author:Robert L. Boylestad
Publisher:Robert L. Boylestad
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Window Detectors The function of a window detector, also called a window comparator, is to indicate when a given voltage falls within a specified band, or window. This function is implemented with a pair of level detectors, whose thresholds VTL, and VTH define the lower and upper limits of the window. Referring to Fig. 9.13a, we observe that as long as VTL <VI < VTH, both Q01 and Q02 are off, so Re pulls vo to Vcc to yield a high output. Should, however, vy fall outside the range, the output BJT of one of the comparators will go on (Qo1 for VI > VTH. Q02 for v1 < VTL) and bring vo near 0 V. Figure 9.13b shows the resulting VTC. If Re is replaced by an LED in series with a suitable current-limiting resistor, the LED will glow whenever v/ falls outside the window. If we wish the LED to glow whenever v, falls inside the window, then we must insert an inverting stage between the comparators and the LED-resistor combination. An inverter example is offered by the 2N2222 BJT of Fig. 9.14. The window detector shown monitors whether its own supply voltage is within tolerance. The top comparator pulls the base of the 2N2222 BJT low whenever Vcc O Qo1 R VO Vec 1/4 Vcc Rs R, R3 LM339 4 3 2 5 R₁₂ 6 1/4 LM339 RA R6 2N2222 1 + 7 12 LM385 2.5 V R₁ 0 10 202 VTL VTH (b) (a) FIGURE 9.13 Window detector and its VTC. drops below a given lower limit, and the bottom comparator pulls the base low whenever Vcc rises above a given upper limit; in either case the LED is off. For Vec within tolerance, however, the output BJTS of both comparators are off, letting Return on the 2N2222 BJT and thus causing the LED to glow. FIGURE 9.14 Power-supply monitor; LED glows as long as Vcc is within specification. Problem #1: Specify suitable component values so that the LED of Fig 9.14 glows for Vcc within the band 5V +/-5%, usually required by digital circuits to work according to specification. Assume VLED is approximately 1.5V, and impose ILED is approximately 10mA and IB(2N2222) is 1mA
Transcribed Image Text:Window Detectors The function of a window detector, also called a window comparator, is to indicate when a given voltage falls within a specified band, or window. This function is implemented with a pair of level detectors, whose thresholds VTL, and VTH define the lower and upper limits of the window. Referring to Fig. 9.13a, we observe that as long as VTL <VI < VTH, both Q01 and Q02 are off, so Re pulls vo to Vcc to yield a high output. Should, however, vy fall outside the range, the output BJT of one of the comparators will go on (Qo1 for VI > VTH. Q02 for v1 < VTL) and bring vo near 0 V. Figure 9.13b shows the resulting VTC. If Re is replaced by an LED in series with a suitable current-limiting resistor, the LED will glow whenever v/ falls outside the window. If we wish the LED to glow whenever v, falls inside the window, then we must insert an inverting stage between the comparators and the LED-resistor combination. An inverter example is offered by the 2N2222 BJT of Fig. 9.14. The window detector shown monitors whether its own supply voltage is within tolerance. The top comparator pulls the base of the 2N2222 BJT low whenever Vcc O Qo1 R VO Vec 1/4 Vcc Rs R, R3 LM339 4 3 2 5 R₁₂ 6 1/4 LM339 RA R6 2N2222 1 + 7 12 LM385 2.5 V R₁ 0 10 202 VTL VTH (b) (a) FIGURE 9.13 Window detector and its VTC. drops below a given lower limit, and the bottom comparator pulls the base low whenever Vcc rises above a given upper limit; in either case the LED is off. For Vec within tolerance, however, the output BJTS of both comparators are off, letting Return on the 2N2222 BJT and thus causing the LED to glow. FIGURE 9.14 Power-supply monitor; LED glows as long as Vcc is within specification. Problem #1: Specify suitable component values so that the LED of Fig 9.14 glows for Vcc within the band 5V +/-5%, usually required by digital circuits to work according to specification. Assume VLED is approximately 1.5V, and impose ILED is approximately 10mA and IB(2N2222) is 1mA
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