⚑ ELT 102 · Digital Logic & Solid State Devices Hands-On Tinkercad Lab
Unit 2 Β· Solid State Devices Β· Lab

Basic Diode Operation: Forward & Reverse Bias

Build a diode test circuit in Autodesk Tinkercad Circuits, measure voltage and current in both bias directions, and prove for yourself that a diode is a one-way valve for current β€” conducting near 0.7 V forward, blocking completely in reverse.

⏱ 60–90 Minutes πŸ–₯ Tinkercad Circuits (Free) πŸ”§ 4 Components Β· 3 Multimeters πŸ“Š Data Tables + I-V Curve Explorer βœ… 6-Question Knowledge Check

Learning Objectives

By the end of this lab, you will be able to:

  • Construct a series diode-resistor circuit on a virtual breadboard in Tinkercad Circuits, correctly identifying the anode and cathode of a 1N4001 rectifier diode.
  • Configure virtual multimeters as an ammeter (in series) and voltmeters (in parallel) to measure circuit current and component voltage drops.
  • Measure the forward voltage drop of a silicon diode and verify that it remains near 0.6–0.7 V while the series resistor absorbs the remaining supply voltage.
  • Demonstrate reverse-bias blocking by flipping the diode and confirming that current falls to 0 A and the full supply voltage appears across the diode.
  • Apply Kirchhoff's Voltage Law and Ohm's Law to predict circuit current β€” I = (VS βˆ’ VF) / R β€” and compare predictions against simulated measurements.
  • Explain why a current-limiting resistor is required in every diode circuit, and predict what would happen without one.
  • Interpret the diode I-V characteristic curve, locating the knee voltage, the forward-conduction region, and the reverse-blocking region.

Key Terms & Concepts

Click any card to reveal its definition. Review these before you build.

The Diode
PN Junction Diode
The Diode
πŸ”„ Click to reveal definition
Definition
A two-terminal semiconductor device formed where P-type and N-type material meet. It conducts current easily in one direction (anode β†’ cathode) and blocks it in the other β€” electronics' one-way valve.
Anode & Cathode
The Diode
πŸ”„ Click to reveal definition
Definition
The diode's two terminals. The anode is the P-side (arrow in the schematic symbol); the cathode is the N-side (the bar, marked by the silver/gray band on the physical package). Conventional current flows anode β†’ cathode.
1N4001
The Diode
πŸ”„ Click to reveal definition
Definition
The workhorse general-purpose silicon rectifier diode used in this lab: rated 1 A forward current and 50 V peak reverse voltage. Tinkercad's default diode models this part.
Barrier (Knee) Voltage
The Diode
πŸ”„ Click to reveal definition
Definition
The minimum forward voltage needed to overcome the junction's depletion region β€” about 0.7 V for silicon (0.3 V for germanium). Below the knee the diode barely conducts; above it, current rises steeply.
Bias Conditions
Forward Bias
Bias Conditions
πŸ”„ Click to reveal definition
Definition
Anode more positive than cathode. The depletion region collapses, the diode conducts, and it drops a nearly constant ~0.7 V regardless of current. The diode acts like a closed switch (plus a small voltage drop).
Reverse Bias
Bias Conditions
πŸ”„ Click to reveal definition
Definition
Cathode more positive than anode. The depletion region widens, only a tiny leakage current flows (β‰ˆ0 in Tinkercad), and the diode acts like an open switch β€” the entire supply voltage appears across it.
Reverse Breakdown
Bias Conditions
πŸ”„ Click to reveal definition
Definition
If reverse voltage exceeds the diode's rating (50 V for a 1N4001), the junction avalanches and conducts heavily β€” destructive for rectifiers, but exploited deliberately by Zener diodes for voltage regulation.
Current-Limiting Resistor
Bias Conditions
πŸ”„ Click to reveal definition
Definition
The series resistor that sets circuit current once the diode is conducting. Because a forward-biased diode holds ~0.7 V almost no matter what, without a resistor the current would be limited only by the supply β€” destroying the diode.
Measurement
Ammeter (Series)
Measurement
πŸ”„ Click to reveal definition
Definition
A multimeter set to A mode measures current and must be wired in series β€” the circuit's current physically flows through the meter. In Tinkercad, break the circuit and insert the meter into the gap.
Voltmeter (Parallel)
Measurement
πŸ”„ Click to reveal definition
Definition
A multimeter set to V mode measures potential difference and connects in parallel β€” across the two terminals of the component under test, without breaking the circuit.
Negative Reading
Measurement
πŸ”„ Click to reveal definition
Definition
A voltmeter reads negative when its red lead sits at the lower potential. In the reverse-bias step, the meter across the diode reads βˆ’7.50 V β€” the magnitude is the full supply, and the sign tells you the polarity is reversed.
KVL Check
Measurement
πŸ”„ Click to reveal definition
Definition
Kirchhoff's Voltage Law: around any loop, the voltage drops must sum to the supply. In this lab: VS = VR + VD in both bias directions β€” your built-in error detector for every measurement row.

πŸ–₯ About the Simulation Tool: Tinkercad Circuits

Autodesk Tinkercad Circuits is a free, browser-based electronics simulator (no installation, runs on Chromebooks). You drag components from a parts panel onto a workspace, wire them on a virtual breadboard that behaves exactly like the real thing, and press Start Simulation to see live meter readings, glowing LEDs β€” and smoke effects if you overload a part. It is ideal for this lab because you can flip a diode around in two seconds and re-measure, something that reinforces the forward/reverse concept far faster than reading about it.

Getting Set Up
Go to tinkercad.com and sign in (use your class join link if your instructor provided one, or create a free personal account). From the dashboard choose Circuits β†’ Create new Circuit. The parts panel is on the right; keep it set to Components: Basic for this lab.
Tinkercad Survival Skills
  • Rotate a selected part with the R key or the rotate icon β€” you will use this to flip the diode.
  • Wire color is changeable from the toolbar after clicking a wire: use red for +, black for βˆ’, green for measurement leads (matching this lab's figures).
  • Component values (resistance, supply voltage, meter mode) are edited in the small inspector window that appears when you click a part while simulation is stopped.
  • Breadboard rows a–e and f–j are connected in vertical groups of five; the center trench isolates the two halves. The long + / βˆ’ rails run horizontally.

πŸ”§ Virtual Parts List

QtyComponent (Tinkercad name)SettingPurpose
1Breadboard (small)β€”Mounting platform for the resistor and diode
1Power Supply7.50 V / current limit 5 AAdjustable DC source (bench-supply style)
1Resistor1 kΞ© (brown-black-red)Current-limiting resistor R1
1Diode1N4001Device under test, D1 β€” gray band = cathode
3Multimeter1 Γ— A mode, 2 Γ— V modeAmmeter (series) + voltmeters across R1 and D1
~8Wiresred / black / greenPower, ground, and meter connections

πŸ“ The Circuit You Will Build

The test circuit is a simple series loop: power supply β†’ ammeter β†’ resistor R1 β†’ diode D1 β†’ back to the supply. Two voltmeters watch R1 and D1 from the sidelines. The schematic below shows the forward-bias configuration; in Part 3 you will rotate D1 180Β° for reverse bias.

7.50 V DC Supply + βˆ’ A M1 Β· Ammeter (series) R1 = 1 kΞ© D1 Β· 1N4001 anode cathode V M2 Β· V across R1 V M3 Β· V across D1 Conventional current I (forward bias): supply + β†’ A β†’ R1 β†’ D1 anode β†’ cathode β†’ supply βˆ’
Figure 1 β€” Diode test circuit (forward bias). The ammeter M1 is in the loop; voltmeters M2 and M3 attach across R1 and D1 with green leads. On the Tinkercad breadboard, R1 bridges the center trench around column 10 and D1 around column 17, with the supply feeding the bottom + and βˆ’ rails β€” exactly as shown in the lab screenshots.

Expected Readings at a Glance

ConfigurationM1 CurrentM2 V(R1)M3 V(D1)Diode acts like…
Forward bias (band toward supply βˆ’)β‰ˆ 6.8 mAβ‰ˆ 6.8 Vβ‰ˆ +0.7 VClosed switch + 0.7 V drop
Reverse bias (band toward supply +)0.00 A0.00 Vβˆ’7.50 VOpen switch β€” blocks everything
Predict Before You Measure
Before running each simulation step, write down what you expect each meter to read and why. Prediction-first measurement is what turns a wiring exercise into learning β€” and your KVL check (VS = VR + VD) must balance in both tables.

πŸ›  Step-by-Step Procedure

Part 1 β€” Build the Circuit (β‰ˆ20 min)

  1. Create the workspace. Sign in at tinkercad.com, open Circuits β†’ Create new Circuit, and rename it "LastName – Diode Lab" using the title field in the upper-left.
  2. Place the breadboard. In the parts panel search for "breadboard" and drag a Breadboard Small to the center of the workspace.
  3. Add the power supply. Search "power supply" and place it to the left of the breadboard. Click it and set the voltage to 7.50 V and the current limit to 5 A in the inspector. Wire its red (+) terminal to the bottom + rail and its black (βˆ’) terminal to the bottom βˆ’ rail of the breadboard.
  4. Place resistor R1. Drag a Resistor so it straddles the center trench at column 10 (one lead in row e, the other in row f). Click it and set the value to 1 kΞ©. Verify the color bands read brown-black-red.
  5. Place diode D1. Search "diode" and place the 1N4001 straddling the trench at column 17. Orient it so the gray cathode band faces down (toward the βˆ’ rail side). Hover over each lead β€” Tinkercad labels them anode and cathode. This is your forward-bias orientation.
  6. Wire the loop. (a) Red wire from the + rail up to column 10, row a (bottom lead of R1). (b) The top lead of R1 (row f, col 10) will connect to the ammeter in the next step. (c) Green wire from the diode's top lead (row f, col 17) toward the ammeter. (d) Black wire from the diode's bottom lead (row a, col 17) down to the βˆ’ rail.
  7. Insert the ammeter (M1) in series. Drag a Multimeter above the breadboard and set its mode to A (ammeter). Wire its black terminal to R1's top lead and its red terminal to D1's top lead. Current now has no path except through the meter.
  8. Attach voltmeter M2 across R1. Place a second multimeter to the left, set mode to V. Connect its leads to the two leads of R1 (red lead on the supply side).
  9. Attach voltmeter M3 across D1. Place a third multimeter to the right, set mode to V. Connect its red lead to the anode and black lead to the cathode of D1, so a forward drop reads positive.

Part 2 β€” Forward-Bias Measurements (β‰ˆ15 min)

  1. Predict. With VS = 7.5 V, VF β‰ˆ 0.7 V, and R = 1 kΞ©, calculate your expected current using I = (VS βˆ’ VF) / R. Record the prediction in Data Table 1.
  2. Simulate. Press Start Simulation. All three meters come alive.
  3. Record. Log M1 (current), M2 (V across R1), and M3 (V across D1) in Data Table 1. M3 should read close to 0.7 V.
  4. KVL check. Verify V(R1) + V(D1) β‰ˆ 7.50 V. If it doesn't balance, a meter is mis-wired β€” stop and fix it.
  5. Explore the knee. Stop the simulation, lower the supply to 3 V, 1 V, and 0.5 V, re-running each time. Watch what happens to current when VS drops below the barrier potential. Record each row.

Part 3 β€” Reverse-Bias Measurements (β‰ˆ10 min)

  1. Flip the diode. Stop the simulation. Click D1 and rotate it 180Β° (press R twice) so the gray band now faces the + side. Reconnect its leads to the same breadboard columns.
  2. Restore 7.50 V on the supply and press Start Simulation.
  3. Record. M1 should read 0.00 A, M2 0.00 V, and M3 βˆ’7.50 V β€” the screenshot at the top of Figure 1's caption shows exactly this state. Log all three in Data Table 2.
  4. Reason it out. With zero current, Ohm's Law forces V(R1) = IΒ·R = 0 β€” so KVL puts the entire supply across the diode. Write one sentence in your report explaining why the M3 reading is negative.
  5. Stress test (optional). Raise the supply toward 30 V. The 1N4001 blocks up to 50 V reverse, so current stays at zero β€” but note in your report what would eventually happen in a real circuit past the breakdown rating.

Part 4 β€” Trace the Characteristic Curve (β‰ˆ15 min)

  1. Sweep forward voltage. With the diode back in forward bias, set the supply to each value in Data Table 3 (0.2 V β†’ 10 V), simulate, and record I and V(D1) at every point.
  2. Plot. Graph I (vertical) versus V(D1) (horizontal) β€” on paper, in a spreadsheet, or by comparing against the interactive I-V Explorer below. Mark the knee.
  3. Conclude. Answer the Analysis Questions, complete the Knowledge Check, and use your browser's Print function on this page (data tables included) to submit your report.
Troubleshooting
Meter reads 0 in forward bias? Check the diode band direction first, then confirm the ammeter is in the loop (not across a component). Ammeter shows a huge current? You wired it in parallel β€” an ammeter is nearly a short circuit. Nothing at all? Make sure both supply wires reach the rails and the simulation is actually running.

πŸ“‹ Data Tables

Type your readings directly into the tables β€” they are preserved when you print this page. Use the Check KVL buttons to verify each measurement set.

Data Table 1 β€” Forward Bias (VS sweep)

V_S (set)Predicted I = (V_Sβˆ’0.7)/1kMeasured I (M1)V(R1) (M2)V(D1) (M3)V(R1)+V(D1)
7.50 V
3.00 V
1.00 V
0.50 V

Data Table 2 β€” Reverse Bias

V_S (set)Measured I (M1)V(R1) (M2)V(D1) (M3)Diode state (open/closed switch?)
7.50 V
15.0 V

Data Table 3 β€” Forward Characteristic Sweep

V_S0.2 V0.5 V0.7 V1.0 V2.0 V5.0 V10 V
I (mA)
V(D1)

πŸ“ˆ Interactive Diode I-V Explorer

This companion simulator models the same series circuit you built in Tinkercad. Adjust the supply voltage and resistor, flip the bias, and watch the operating point slide along the diode's characteristic curve. Compare its readouts against your Data Table values β€” they should agree closely.

What To Notice
In forward bias, cranking VS from 2 V to 15 V barely moves VD (it creeps from ~0.65 V to ~0.75 V) while the current β€” set almost entirely by R1 β€” climbs linearly. That near-constant drop is why engineers model a conducting silicon diode as a flat 0.7 V. In reverse, the operating point pins to the axis at I = 0 no matter what you do.

✍ Analysis Questions

Answer in complete sentences in your lab report.

  1. Using your Data Table 1 row for 7.50 V, show the KVL calculation proving your three meter readings are consistent with each other.
  2. In forward bias you raised VS from 1 V to 7.5 V, yet V(D1) barely changed. Where did the "extra" voltage go, and which component controlled the current?
  3. At VS = 0.5 V forward, the current was essentially zero even though the diode was pointed the "right" way. Explain using the concept of barrier potential.
  4. In reverse bias, why does the voltmeter across R1 read 0.00 V? Support your answer with Ohm's Law.
  5. Why does M3 read βˆ’7.50 V rather than +7.50 V in the reverse-bias configuration?
  6. Suppose a classmate builds this circuit with no resistor β€” diode straight across the 7.5 V supply, forward biased. Predict what happens and why. (Tinkercad will show you smoke; a real 1N4001 gives you about one second of regret.)
  7. Name one real-world circuit that depends on the diode's one-way behavior you just demonstrated, and describe the diode's job in it in one sentence.

Key Facts Reference Box

Silicon knee voltage
β‰ˆ 0.7 V (Ge β‰ˆ 0.3 V)
Forward diode model
Closed switch + 0.7 V drop
Reverse diode model
Open switch, I β‰ˆ 0
Circuit current (forward)
I = (V_S βˆ’ 0.7 V) / R
Lab values: 7.5 V, 1 kΞ©
I β‰ˆ 6.8 mA Β· V_R β‰ˆ 6.8 V
Reverse-bias readings
0.00 A Β· 0.00 V Β· βˆ’7.50 V
1N4001 ratings
1 A forward Β· 50 V reverse
Cathode identification
Gray/silver band on package
Ammeter wiring
In series (in the loop)
Voltmeter wiring
In parallel (across the part)

Interactive Knowledge Check

Six questions drawn directly from the lab. Select an answer for each, then press Grade My Quiz.

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