Question

In this step, you will add a second transistor, causing the switching action to improve dramatically. The circuit is shown in Figure 10-2. Notice that the 1.0 k resistor is now the collector resistor for Q. The circuit works as follows. When Vw is very low, Q, is off since it does not have sufficient base current. Q, will be in saturation because it can obtain ample base current through Re, so the LED is on. As the base voltage for Q is increased, 0, begins to conduct. As Q, approaches saturation, the base voltage of Q, drops, causing it to go from a saturated to cutoff condition rapidly. The output voltage of Q, drops and the LED goes out. Construct the circuit, and test it as described in the next step. Voc- +12 v Table 10-3 Measured Quantity Ra Vix (LED on) Rei VOUT (LED on) 10 k2 VIN (threshold) 2. Vout (threshold) 2N3904 R 10 kO 1 Value 1.0 kg LED 2 Vour R3 ww 10 k 2 2N3904 IN Figure 10-2 Set the potentiometer so that V is a minimum (OV). Since Q, is off, the LED should be be on. Measure Vix and Vout and record the readings in Table 10-3 in the first two rows. Monitor Vix and slowly increase Vix while watching the LED. You should observe that there is no dim condition for the LED - it will suddenly go off as the input voltage is increased. Record Vin and Vour at the threshold where the LED just turns off. Notice that the output voltage indicates Q, is either in saturation or in cutoff. In step 5, the switching threshold was distinct; however the threshold voltage is rather low and it is susceptible to noise on the input. There is another simple improvement you can make to this circuit. The improvement is shown in Figure 10-3. The common-emitter resistor, Re, will raise the threshold voltage. In addition, because of the different saturation currents of the two transistors, the threshold will be different when the output is in cutoff than when the output is saturated. This is a very useful feature, called hysteresis, and is characteristic of Schmitt trigger circuits (to be investigated in Experiment 22). Modify the circuit from step 5 by adding the 3300 resistor; then test it according to the procedure in the next step. LED.
can you show where to measure, the quantity listed in the pic?

like what two points to get the answer

for all of them, please.

Answer 1

Answered the question below.

If you have any doubts please ask in comment section.

1) Measuring of Vin(LED,ON) and Vout (LED,ON) :

Vin(LED,ON) = 1.172 uV =~ 0V

Vout(LED,ON) = 85.112 mV

vi 12V HA Rc2 160 Multimeter-XMM1 х XMMI 1 LED1 85.112 mV A V 2 dB VOUT Rc1 1050 Set... Q2 2N3904 R1 1050 100 % Key-A · Rb Q1 2N3904 5 10kg XMM2 Multimeter-XMM2 х Vin 1.172 V A V 2 dB ~ Set...

2) Measuring of Vin (threshold) and Vout(threshold) :

Vin(threshold) = 1.156 V

Vout(threshold) = 10.992 V

vi 12V Rc2 1k02 XMMI LED1 Multimeter-XMM1 10.922 V VOUT Rc1 1050 A V 2 dB Q2 2N3904 + Set... R1 10KQ : 90 % Key A Rb Q1 2N3904 100 XMM2 Multimeter-XMM2 х Vin 1.156 V A V 12 dB . Set...