Video summary

Electronics 1, Lab 10, BJT Characteristics curve using Multisim

Main summary

Key takeaways

Educational

Main ideas / concepts covered

  • Purpose of Lab 10: Determine and plot BJT DC characteristics curves using Multisim, focusing on how transistor currents change with applied voltages.
  • Transistor types: Both NPN and PNP behavior are discussed, including how to identify leads and confirm transistor type.
  • Key BJT terms and variables:
    • Leads: Emitter, Base, Collector
    • Voltages: VBE (base-emitter voltage), VCE (collector-emitter voltage), also VBB / VCC as DC bias sources used in simulation
    • Currents: IB (base current / input current), IC (collector current / output current)

What characteristics are plotted

  • Output characteristic curve: relationship between IC vs VCE (for different IB / base-bias values).
  • Input characteristic curve: relationship between IB vs VBE (for different VBE values as swept).

Speaker / source information (implied in subtitles)

  • The video contains an instructor/teacher speaking to “students” and explaining the lab procedure and theory.

Methodology / instruction-like content (detailed steps)

A) How to identify transistor leads (Emitter/Base/Collector) using a multimeter — Method 1 (Diode mode)

  1. Set the multimeter mode to “Diode.”
  2. Understand what readings mean:
    • A forward-biased junction gives a specific reading.
    • A reverse-biased junction shows “open loop” or “1” (out-of-range).
  3. Check for NPN vs PNP using diode-mode lead connections:
    • For NPN identification:
      • Connect positive lead to Base.
      • Connect negative lead to either Emitter or Collector.
      • If you get a specific diode-like reading, it indicates NPN.
      • If you reverse those connections (positive to the “mid” terminal and negative to the other lead), you should see open loop / 1.
    • For PNP identification:
      • The mid terminal is Base, but the polarity expectation flips.
      • Connect negative lead to the midpoint (Base).
      • Connect positive lead to Collector or Emitter.
      • If you get a specific reading, it indicates PNP.
      • Reversing the polarity should give open loop / 1.
  4. If required: adjust the measurement range (the instructor notes that “1” can be removed by changing the range until a meaningful value appears).

B) How to identify transistor leads using HFE mode — Method 2 (multimeter transistor tester)

  1. Switch the multimeter to “HFE” mode (or the transistor parameter setting).
  2. Use the multimeter’s labels/pin mapping corresponding to transistor slots (shown as patterns for Emitter/Base/Collector positions).
  3. If the transistor is NPN (unknown initially):
    • Try one standard lead order:
      • Emitter – Base – Collector
    • If the multimeter shows a value (not “1” / open / invalid), the lead order is likely correct.
  4. If that order fails:
    • Try the alternate correct ordering shown for NPN in the multimeter’s layout:
      • Base – Collector – Emitter (as described)
  5. If neither NPN ordering yields a valid HFE reading:
    • Repeat the process for PNP using the corresponding lead-order orientation in the HFE tester.
  6. Note on HFE meaning:
    • HFE = DC current gain / beta (a measure of gain in DC conditions).

C) Multisim lab workflow — plotting BJT DC characteristics

A general concept of the graphs

  1. Output characteristic graph:
    • Axes: IC (collector current) vs VCE (collector-emitter voltage)
    • Measured for multiple base current values (IB).
  2. Input characteristic graph:
    • Axes: IB (base/input current) vs VBE (base-emitter voltage)

Simulation procedure (as described)

  1. Components used:
    • 1 transistor: 2N3904
    • Resistors: 33 kΩ and 100 Ω
  2. Build the circuit in Multisim:
    • Include indicators/probes (for current and voltages) and meters as needed.
  3. Choose analysis type:
    • Use DC analysis (DC behavior is for initial characteristics; amplifying AC requires additional conditions/power).
  4. Perform the input-side sweep (IB vs VBE):
    • Sweep a source from 0 to 10 with a step size of 2.
    • Set up:
      • Input voltage source (VBB / VBE-related) as the swept variable.
      • Output variable (y-axis) as base current IB.
    • Observe curves (multiple traces for different sweep values).
  5. Perform the output-side sweep (IC vs VCE):
    • In DC sweep/analysis, vary collector voltage / VCC range (ranges mentioned include -5 to +5, later focusing on a smaller interval such as -2 to 5).
    • Set up:
      • x-axis: VCE
      • y-axis: IC
      • Multiple curves correspond to different base biases / IB levels (different VBB values).
  6. Make plots and export data:
    • Ensure you can see curves for multiple VB values (example list: VB = 0, 2, 4, 6, 8, 10).
    • Export traces for all required conditions.
    • Save/export results into an Excel sheet.
  7. Compute and annotate missing values:
    • For each case VB = 2, 4, 6, 8, 10, calculate collector current IC corresponding to those conditions.
    • Also compute/record IB values (units may appear as microamperes/milliamperes depending on the reading).
  8. Lab submission expectations:
    • Include:
      • Both graphs (input and output characteristic)
      • Data sheet / exported Excel data
      • Any calculated IC values and corresponding base values

Main lessons / takeaways

  • Multimeter diode mode can identify transistor type (NPN/PNP) and help determine which lead is base versus emitter/collector.
  • HFE mode can more directly confirm lead configuration and provide beta (DC gain) when connected correctly.
  • Multisim DC analysis generates:
    • IC–VCE output curves (vary VCE for fixed IB/base-bias levels)
    • IB–VBE input curves (vary VBE/input bias)
  • Proper documentation includes exported traces and computed values for multiple bias conditions.

Speakers / sources featured

  • Instructor / teacher (unnamed): explains Lab 10, transistor identification methods, and Multisim simulation steps.

Original video