Bootstrap Sweep Circuit

Pre-Lab:

1. Study the operation and working principle of Boot-strap Sweep Circuit.
2. Study the procedure for conducting the experiment in the lab.

Objectives:

1. To design a Boot-strap Sweep Circuit.
2. To obtain a sweep wave form.

Components Required:

1. Resistors – 100kohms , 5.6kohms, 10 Kohms  - 1 each
2. Capacitors – 0.1microF, 10microF, 100microF  - 1 each
3. IN4007 Diode – 1 No.
4. 2N2369 Transistors – 2 Nos.
5. Bread Board

Apparatus Required:

1. Power supply (0V-30V)
2. CRO(1Hz-20MHz)
3. Signal generator (1Hz-1MHZ)
4. Connecting Wires.

Circuit Diagram:

Theory:

The input to Q₁ is the gating waveform. Before the application of the gating waveform, at t = 0, transistor Q₁ is in saturation. The voltage across the capacitor C and at the base of Q₂ is V_CE(sat). To ensure Q₁ to be in saturation for t = 0, it is necessary that its current be at least equal to I_CE / h_FE so that R_b < h_feR.

With the application of the gating waveform at t = 0, Q₁ is driven OFF. The current I_C1 now flow into C and assuming unity gain in the emitter follower V₀. When the sweep starts, the diode is reverse biased, as already explained above, the current through R is supplied by C₁. The current V_CC / R through C and R now flows from base to emitter of Q₂.if the output V₀ reaches the voltage V_CC in a time T_S / Tg, then from above we have T_S = RC.

Procedure:

• Connect the circuit as shown in figure.
• Apply the square wave or rectangular wave form at the input terminals.
• Connect the CRO at output terminals now plug the power card into line switch on and observe the power indication.
• As mentioned in circuit practical calculation. Observe and record the output waveforms from CRO and compare with theoretical values.

Expected Waveforms:

Inference: Conclusions can be made on sweep time T_S and retrace time T_R and sweep voltage V_S of the sweep waveform theoretically and practically and also made on if the output waveform of the Bootstrap are identical with the theoretical wave forms or not.

Viva Questions:

1. Define (a) Voltage time base generator, (b) current time base generator (c) linear time base generator.                   

Ans:

1. A voltage time-base generator is one that provides an output voltage waveform, a portion of which exhibits a linear variation with time.
2. A current time-base generator is one that provides an output current wave form, a portion of which exhibits a linear variation with time.
3. A linear time-base generator is one that provides an output waveform a portion of which exhibits a linear variation of voltage or current with time.

2. What is the relation between the slope error, displacement error and transmission error?

Ans: The relation between slope, displacement and transmission is given as es = 2et = 8ed.

3. What are the various methods of generating time base wave-form?

Ans: The methods of generating a time-base waveform are exponential charging, constant current charging, the miller circuit, the phantastron circuit, the bootstrap circuit, compensating networks, an inductor circuit.

4. Which amplifier is used in Boot-strap time base generator?

Ans: In bootstrap time-base generator, a non inverting amplifier with unity gain is required.

5. Which type of sweep does a bootstrap time-base generator produce?

Ans: A bootstrap time-base generator produces a positive-going sweep.

6. What is the gain of the amplifier used in Bootstrap time base generator?

Ans: In bootstrap time-base generator, a non inverting amplifier with unity gain is required.

7. What is retrace time? Write the formula for the same for Bootstrap time base generator.

Ans: The time taken by signal to return to its initial value is called retrace time. The retrace time is given by Tr = (CV_S / V_CC)/(h_FE/R_B) - (1/R).

8. What is the formula for sweep amplitude in Bootstrap time base generator?

Ans: The formula for sweep amplitude in bootstrap time base generator is given as V_S = V_CCTg / RC.

9. To have less flatness time of sweep signal, then the gate signal time has to be __.

Ans: To have less flatness time of sweep signal, then gate signal(Tg) has to be equivalent to sweep time (Ts).

10. A Bootstrap sweep circuit employs __ type of feedback.

Ans: A bootstrap sweep circuit employs positive feedback.

Design problem:

1. Design Boot-strap Sweep Circuit with sweep amplitude of 8V, with sweep interval of 1ms neglect flyback time and e_s = 0.25.
2. Design Boot-strap Sweep Circuit with sweep amplitude of 15V, with sweep interval of 2ms neglect flyback time and e_s = 0.1.

Outcomes: After finishing this experiment students are able to Design Boot-strap sweep circuit and able to generate a sweep voltage waveform.