1) 2) =23 3) 4) 5) HW# 4 Name TRUE/FALSE. Write "T" if the statement is true and 'F' if the statement is false. 1) The base region of a BJT is heavily doped and wide compared to the other two regions. 2) When a BJT is conducting, the collector current is identical to the emitter current. 3) The BDC for a BJT is the ratio of collector current to emitter current. 4) A saturated BJT has maximum collector current. 5) Assume a transistor has a maximum power rating of 1 W and VCE -5 V. If Ic = 120 mA, the power rating is not exceeded. 6) The voltage gain of a BJT amplifier is directly proportional to the internal ac emitter resistance. 7) Photo transistors have the greatest sensitivity to blue light. 6) 7) MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 8) In a certain BJT, the collector current is 22.0 mA when the base current is 100 pA. The emitter current is A) 21.9 mA B) 2.2 mA C) 22.0 mA 8) D) 22.1 mA 9) The value of BDC is the ratio of A) collector current to base current C) collector current to emitter current 10) Typical values of aDC are from A) 1.00 to 10 B) 800 to 1000 B) emitter current to base current D) none of the above C) 0.95 to 0.99 01 10) D) 20 to 200 11) D) 50 V 11) A forward-biased npn transistor has a typical voltage drop from base to emitter of A) 1.5 V B) 0.7 V C) 10 V 4-10▸ R₁ R180 BB VR+ ww 33 ΚΩ 6 V Figure 1 Voc 15 V 12) Refer to Figure 1. Assume BDC 200. The expected value of IB is A) 161 A B) 182 A C) 200 μA 13) Refer to Figure 1. Assume BDC - 200. The value of VCE is approximately A) 5.8 V B) 9.2 V 14) Refer to Figure 1. If VCC is increased to 18 V. IB will C) 7.5 V A) increase B) decrease 12) D) 80 A 13) D) 12.4 V 14) C) not change VCE 0.7 V Figure 2 A characteristic curve 15) For the characteristic curve in Figure 2, the region between A and B is called the A) breakdown region C) cutoff region B) active region D) saturation region 16) For the characteristic curve in Figure 2, the equation IC BDC/B is true A) only beyond C on the curve C) only between B and C on the curve 17) ICEO is A) collector current when the transistor is cutoff B) base current when the transistor is saturated C) collector current when the transistor is on D) collector current when the transistor is saturated 18) If a BJT is saturated. 15) 16) B) at no place on the curve D) only between A and B on the curve 17) A) both base current and collector current are at a maximum B) VCC appears between the collector and emitter C) base current is at maximum D) collector current is at maximum 19) If a BJT is saturated. A) VCE is approximately 1/2 VCC C) VCE is near zero 18) 19) B) VCE is approximately equal to VCC D) none of the above 3 V₁ BB+ 2.5 V Re≥500 RB Voc ww 18 ΚΩ Boc-200 Figure 3 The transistor has the following ratings: PD (max) = 650 mW. VCE (max) = 40 V. and IC(max) = 200 mA. 20) Refer to Figure 3. The maximum value that VCC can be adjusted to without exceeding the VCE(max) rating is (ignore other max ratings). A) 60 V B) 40 V C) 45 V 21) Refer to Figure 3. If VCC is set to 48 V. PD(max) is exceeded by A) 110 mW B) 80 mW 20 D) 50 V 21) C) 310 mW D) 55 mW 22) C) in the linear range 23) C) Av D) PD(max) 22) Refer to Fig 3. Assume VCC is lowered to 15 V. The transistor is A) cutoff B) saturated 23) The symbol hFE means the same as B) BDC A) DC 24) HFE varies with A) temperature B) collector current C) both A and B D) none of the above 25) A 10 mV ac signal is applied to the base of a properly biased transistor with RC = 1.2k and r = 36. The output ac voltage is A) 152 mV B) 33 mV C) 333 mV D) 105 mV 24) 220 25) VBB 4.0 V RB ww Κ Ε 1.5 ΚΩ Vcc=15 V Poc=100 Figure 4 26) Refer to Figure 4. Assume RB-22 kg. The collector current will be approximately A) 10 mA B) 5 mA C) 20 mA 27) Refer to Figure 4. The largest base resistor that will still saturate the transistor is approximately Α) 33 ΚΩ Β) 330 ΚΩ 28) Refer to Figure 4. If RB-100 k2, Vc is approximately A) 12.5 V B) 10 V C) 40 k C) 7.5 V 26) D) 27 mA 27) D) 400 k 28) D) 5 V 29) 29) Refer to Figure 4. If you wanted to change the transistor to a pnp type, you need to A) increase the base resistor B) increase the collector resistor C) change both de sources to negative supplies D) all of the above Voc=+10.0 V Re 330 Ω OV 3V RB ww Ppc=100 2.2 ΚΩ Figure 5 30) Refer to Figure 5. When conducting, assume the LED drops 1.8 V and VCE(sat) - 0.2 V. If the input square wave is +3.0 V, the current in the LED will be approximately A) 136 mA B) 24 mA C) 105 mA 31) The NAND gate is a digital circuit that produces a A) HIGH level signal when both inputs are LOW B) LOW level signal when both inputs are HIGH C) HIGH level signal when both inputs are HIGH D) LOW level signal when both inputs are LOW 32) The NOR gate is a digital circuit that produces a A) HIGH level signal when one or more inputs are HIGH B) LOW level signal when one or more inputs are LOW C) HIGH level signal when one or more inputs are LOW D) LOW level signal when one or more inputs are HIGH 33) In switching circuits, a transistor operates between A) cutoff and saturation C) active region and breakdown 34) The light sensitive region of a photo transistor is the B) collector A) base C) emitter 30) D) 30 mA 31) 32) 33) B) cutoff and active region D) none of the above 34) D) substrate R 3.3 ΚΩ Ic (mA) 10- 50 mW/cm2 V+24.0 V 8- 40 mW/cm² 30 mW/cm2 20 mW/cm2 10 mW/cm² Dark current 10 Va(V) Figure 6 A phototransistor and its characteristic curve 35) Refer to Figure 6. Assume you measure VOUT as 11 V. From this, you can conclude that the light intensity is approximately 35) A) 20 mW/cm² B) 30 mW/cm² 36) The primary purpose of an optocoupler is to A) couple an LED to a relay C) isolate certain sections of circuits C) 40 mW/cm² D) 10 mW/cm2 36) B) amplify light D) convert light into electrical current 37) C) base D) substrate 38) 37) The metal mounting tab or case of a power transistor is connected to the A) emitter B) collector 38) Small signal transistors are available in A) dual in line (DIP) packs C) quad small outline (SO) packs B) plastic or metal cases D) all of the above VBB +3 V RB w 56 k 3.0v Vcc +9 V Re 560 2 9.0v 2N3904 Figure 7 39) Refer to Figure 7. Assume a single problem accounts for the readings. From the readings, you can conclude that A) the base-collector junction is open C) RC is shorted 40) Refer to Figure 7. The transistor is A) in the active region C) cutoff D) Rg is open 39) B) the base-emitter junction is open 40) B) saturated D) in the breakdown region