Practical case: Half-wave rectification with 1N4007

Materials

• 1x 1N4007 silicon diode (D1)
• 1x 1 kΩ resistor, 0.25 W (R1, load)
• 1x Function generator (sine, up to 10 Vrms, 50/60 Hz) or low‑voltage AC source (≤12 Vrms)
• 1x Oscilloscope (2 channels) or multimeter (AC and DC modes)
• 1x Breadboard and jumper wires
• Optional: 1x 100 µF electrolytic capacitor, ≥25 V (for later smoothing test)
• Optional: 2x Oscilloscope probes with ground leads or DMM probes

Wiring guide

• Place R1 so one end will go to ground (GND) and the other to the output node (Vout).
• Insert D1 in series above R1: anode at the top node, cathode toward R1. The 1N4007’s band marks the cathode.
• Connect the function generator:
• Generator signal (hot) to the top node (this is Vin).
• Generator ground to the ground rail (GND).
• Connect R1’s bottom lead to the ground rail (GND).
• Abbreviations used:
• Vin: input sine node from the generator, measured to GND.
• Vout: node between D1 and R1, measured to GND.
• Vd: diode forward drop, defined as Vd = Vin − Vout (anode minus cathode in this topology).
• Double‑check polarity: top node → D1 (anode up, cathode down) → Vout → R1 → GND → generator ground.

Schematic

      Generador de señales (seno, 10 Vpp, 50 Hz, 0 V offset)
      +V
      Vin ──────────●CH1───────────────┐
                                      │
                                      │
                                     ┌┴┐
                                     │ │
                                     │ │
                                     └┬┘   D1: 1N4007
                                      │
                                      ├──────────●CH2 ●VM+
                                      │
                                     ┌┴┐
                                     │ │
                                     │ │
      Tierra del generador ──────────┴┬┘   RL: 1 kΩ (carga)
                                       │
                                      ●REF
                                       │
                                      GND

Measurements and tests

• • Important setup:
  • Set the generator to a sine wave, 5 Vrms at 50 or 60 Hz, 0 V DC offset.
  • If using an oscilloscope, set channel coupling to DC for both channels.
• • Verify connections:
  • Check D1 orientation: band (cathode) must face down toward R1.
  • Confirm generator ground and R1 bottom both go to the same GND.
• Waveforms:
  • • Observe Vin (CH1) at the ● Vin point and Vout (CH2) at the ● Vout point.
  • You should see a full sine at Vin and only the positive half‑cycles at Vout (clipped near zero on negative half‑cycles).
• Diode drop (Vd):
  • • Vd is defined as Vd = Vin − Vout (anode minus cathode).
  • Using the scope: use CH1 = Vin and CH2 = Vout; display CH1−CH2 (math) to see Vd directly.
  • Using a DMM: measure Vin to GND and Vout to GND; subtract readings at the same instant (or use scope for accuracy).
  • Expect about 0.6–0.9 V when the diode conducts (near Vin’s peaks).
• DC level at Vout (no capacitor):
  • • Measure the average (mean) of Vout with the scope’s measurement function or a DMM in DC mode.
  • Expect a small positive average (approximately Vpk/π minus the diode drop effect), not a smooth DC.
• Load current:
  • • Compute Iout(t) ≈ Vout(t) / R1 during conduction.
  • Peak load current ≈ (Vpk − Vd) / R1, where Vpk ≈ 1.414 × Vrms.
• Frequency check:
  • • Change frequency (e.g., 100–500 Hz). The waveform shape remains a half‑wave; amplitudes don’t change (ideal source), but scope timebase will.

Common mistakes

• Reversing D1 (band up) blocks positive half‑cycles, yielding near‑zero Vout.
• Missing common ground between the generator and the circuit causes incorrect measurements.
• Using too large a Vrms with a low‑voltage resistor can overheat R1; stick to ≤10 Vrms with 1 kΩ/0.25 W.

Safety notes

• Do not connect directly to mains. Use only a function generator or an isolated low‑voltage AC source (≤12 Vrms).
• The 1N4007 is suitable for line‑frequency rectification; keep currents within safe limits for your resistor’s power rating.

Improvements and extensions

• Add smoothing capacitor: place 100 µF from Vout to GND (observe polarity: + at Vout).
• You’ll see Vout become a pulsed DC with ripple; measure ripple ΔV versus load and frequency.
• Try different loads (e.g., 470 Ω, 2.2 kΩ) and observe how conduction angle and peak current change.
• Replace D1 with a Schottky diode (e.g., 1N5819) to observe lower Vd and higher Vout.

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Carlos Núñez Zorrilla

Electronics & Computer Engineer

Telecommunications Electronics Engineer and Computer Engineer (official degrees in Spain).

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