Lab 9 RS

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Lab 9: Diode Circuits

Clipping Circuit

1.) Construct the circuit shown below using a silicon diode.

2.) Use a sine wave generator to drive the circuit so $V_{in} = V_0 \cos(2 \pi \nu t)$ where $V_0 = 0.1$ V and $\nu$ = 1kHz. (20 pnts)

3.) Based on your observations using a oscilloscope, sketch the voltages $V_{in}$ and $V_{out}$ as a function of time.

4.) Do another sketch for $V_0$ = 1.0 V and another for 10.0 V (DONT LET ANY SMOKE OUT!). (20 pnts)

Differentiating Circuit with clipping

1) Construct the circuit below.

2) Select $R_1$ and $R_2$ such that the current from the +5V DC source is less than 1.0 mA and the DC voltage at $V_{out}$ is 3 V when there is no input pulse.

Because we want to keep the current below $1\ mA$ and using $I = \frac{V}{R_1+R_2} \leq 1\ mA$. Solving this inequality we get the first condition for $R_1$ and $R_2$

 [math]1)\ \ R_1+R_2 \geq \frac{5\ V}{1\ mA} = 5\ k\Omega[/math]

Also because we want $V_{out} = 3\ V$ and using $V_{out} = V_{in}\cdot\frac{R_2}{R_1+R_2}$. Without any input pulse $V_{in} = 5\ V$. Solving this simple equation we get the second condition for $R_1$ and $R_2$

 [math]2)\ \ R_2 = 1.5\ R_1[/math]

I am going to use [math]R_1 = 2\ k\Omega[/math] and [math]R_2 = 3\ k\Omega[/math] which satisfy both conditions above

3) Select a capacitor $(C)$ and a pulse width $\tau$ to form a differentiating circuit for the pulse from the signal generator. Hint: $R_{12}C \ll \tau$.

Taking $(R_1 + R_2) = 5\ k\Omega$ and $C_{out} = 1.255\ \mu F\ \Rightarrow RC = 6.28\ ms$.

And choosing the the pulse width $\tau \approx 80\ ms \gg 6.28\ ms$ I will be able to make a good differentiator circuit.

4) plot $V_{in}$ and $V_{out}$ as a function of time using your scope observations. (20 pnts)

5) Now add the diode circuit from part 1 to prevent $V_{out}$ from rising above +5 V. Sketch the new circuit below.

6) plot $V_{in}$ and $V_{out}$ as a function of time with the diode circuit you added using your scope observations. (the diode should clip off positive spikes) (20 pnts)

Questions

1. Explain your results in parts 1 & 2 in terms of the diode turn-on voltage. (20 pnts)

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