Math Problem Statement

find the ans

Find Rc and Rb, in the circuit if Vcc = 10V and VBB = 5V, so that Ic = 10mA and VCE = 5V. A silicon transistor with beta = 100, VBE = 0.7V, and negligible reverse saturation current is under consideration.

Solution

Let's solve the problem step by step, where we need to find the resistances RCR_C and RBR_B for the given circuit.

Given Data:

  • VCC=10VV_{CC} = 10 \, \text{V}
  • VBB=5VV_{BB} = 5 \, \text{V}
  • IC=10mA=0.01AI_C = 10 \, \text{mA} = 0.01 \, \text{A}
  • VCE=5VV_{CE} = 5 \, \text{V}
  • VBE=0.7VV_{BE} = 0.7 \, \text{V}
  • β=100\beta = 100 (current gain)
  • Negligible reverse saturation current

Step 1: Finding RCR_C

We can use Kirchhoff's Voltage Law (KVL) in the output loop: VCC=ICRC+VCEV_{CC} = I_C R_C + V_{CE} Rearranging to solve for RCR_C: RC=VCCVCEICR_C = \frac{V_{CC} - V_{CE}}{I_C} Substitute the known values: RC=10V5V0.01A=5V0.01A=500ΩR_C = \frac{10 \, \text{V} - 5 \, \text{V}}{0.01 \, \text{A}} = \frac{5 \, \text{V}}{0.01 \, \text{A}} = 500 \, \Omega

So, RC=500ΩR_C = 500 \, \Omega.

Step 2: Finding RBR_B

First, calculate the base current IBI_B using the relation between collector current ICI_C and IBI_B: IB=ICβI_B = \frac{I_C}{\beta} Substitute the known values: IB=0.01A100=0.0001A=100μAI_B = \frac{0.01 \, \text{A}}{100} = 0.0001 \, \text{A} = 100 \, \mu\text{A}

Next, apply KVL in the input loop: VBB=IBRB+VBEV_{BB} = I_B R_B + V_{BE} Rearranging to solve for RBR_B: RB=VBBVBEIBR_B = \frac{V_{BB} - V_{BE}}{I_B} Substitute the known values: RB=5V0.7V0.0001A=4.3V0.0001A=43kΩR_B = \frac{5 \, \text{V} - 0.7 \, \text{V}}{0.0001 \, \text{A}} = \frac{4.3 \, \text{V}}{0.0001 \, \text{A}} = 43 \, \text{k}\Omega

So, RB=43kΩR_B = 43 \, \text{k}\Omega.

Final Answer:

  • RC=500ΩR_C = 500 \, \Omega
  • RB=43kΩR_B = 43 \, \text{k}\Omega

Would you like further details on the calculations or clarification on any steps?

Here are some related questions to further explore this topic:

  1. How would changing the value of VCCV_{CC} affect RCR_C?
  2. What happens if β\beta (current gain) is doubled?
  3. How does the choice of RBR_B influence the stability of the circuit?
  4. Can we calculate the emitter current IEI_E from the given values?
  5. How would the circuit behavior change if VBEV_{BE} is 0.6V instead of 0.7V?

Tip: In BJT circuits, small changes in β\beta can significantly affect base current, so stability techniques (like feedback) are often used to minimize this impact.

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Math Problem Analysis

Mathematical Concepts

Ohm's Law
Kirchhoff's Voltage Law (KVL)
Transistor Basics

Formulas

Rc = (Vcc - Vce) / Ic
Ib = Ic / beta
Rb = (VBB - VBE) / Ib

Theorems

Kirchhoff's Voltage Law

Suitable Grade Level

Undergraduate level (Electrical Engineering)