Question

Use the diagram to solve. The ideal Op-amp represents an amplified output from a sensor (Va) to an alarm represented by the transistor. The LED will light to show a warning when the sensor voltage reaches a certain threshold. Let Vcc = 12V DC, R1 = 1812, R2 = 212, R3 = 20532, R4 = 30032. The voltage drop for the LED is 0.7V and the transistor's beta is 80. (a) The sensor output Va = 200mVDC. Solve for V. Solve for Ifor the transistor and solve for Vout for the transistor. Will the LED light to show a warning? (7.5 points) (b) The sensor output Va = 1.6VDC. Solve for V. Solve for I, for the transistor and solve for Vout for the transistor. Will the LED light to show a warning? (7.5 points) Voc R2 Vem Vout

Answer 1

Vec R, IK , R=2kr., R₂ = 20kr, Ry=3000, B=80 Varop for LED = 0.70 Va= 200mv Var 200 x103 v. e According to virtual ground. V = va = 200x103 v. Apply Kél at sode "b" ovo - vb ve Roo Rd

200X10 0 - - 2007.03 2 x 103 3,18103 -3 200x10 - Va - 200x10 = coxo = 2.000 vnd -- 400X10 --3 200X10 - V = 600xio 3v. off Transiston vse.= 0.6V will be in cut x=0.or which is uge = 0.7 v. Ag Vg = ress than open will be Transistor .. 18 = 0 A ge= BSB ç -

AS Je=0 Vout - Voc – v drop LED 12 - 007 Vout LED wont 11-30 glow © Voz 16 V According to virtual ground a = b = 16V Apply Ker Rg R, 16- Voe - O = 2x103. 1X103 1e6-e = Ve= – 1.6x2 4.6x2 + 206

Va = 4.80 at Base Emitter Now junction x= Apply xvL of transist To Rz +UBE VBE=0.7) 4.85 Sat 20x10 +0.7 Gel GgX 20x10 = 4.7 208103 AB= --3 So = 0.205 810 A = 8 GB = 80X0.205 81o3. Ju = 16. 4x108 A Vee = Varop & Ru + Vout 2 = 0.7 + 86.4x10²x 300 + Vout 12=0.7+ 4.92 thout You = 6.38 v LED will glow.

مگر Given 2 R2 » aux Vout ivec it can be se drawn Yout According to virtual ground voltag at node bh will equal to voltage = Va. to ground & R is connected Voltage. Vb

when ever a Resistor is connected to two different voltage levels than voltage drop across at that Resistor for R Resister R is connected box e and transito V R3 case a ; V207 VOE=0.71) , transistor will be open open circuit means No potential difference i no votage drop case) - voltage drop is present across R , vaso7

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