Diodes, Transistors, and Lead-Acid Batteries: Key Concepts

Posted on Mar 18, 2025 in Technology

Diodes: Semiconductor Devices

A diode is a semiconductor device that allows electric current to pass in one direction, behaving similarly to a switch. The characteristic curve of a diode (IV) consists of two regions: below a certain potential difference, it acts like an open circuit (non-conducting), and above it, it acts like a closed circuit with very small electrical resistance. Because of this behavior, diodes are often called rectifiers, as they can suppress the negative part of any signal as an initial step in converting alternating current into direct current.

Types of Diodes:

  • Zener Diode: A special type of diode always used in reverse bias. When biased in the forward direction, it behaves like a common rectifier diode. However, when reverse biased, it maintains a constant voltage at its terminals.
  • Varicap: Also known as a variable capacitance diode, it behaves like a variable capacitor controlled by voltage.
  • Photodiode: A diode sensitive to light intensity. Increasing light increases the reverse saturation current. When reverse biased and not exposed to light, very little current passes. When exposed to bright light, current flow increases significantly.
  • LED (Light Emitting Diode): When forward biased, current passes directly, and from a certain voltage point, it emits light. The brightness increases with current. LEDs support low current and voltage.

Transistors: Electronic Components

A transistor is an electronic component formed by three crystals. It uses a small drive current to control a larger current. It can operate as a switch (relay) or amplifier. For a PNP transistor, the emitter and collector must measure N relative to the base. For an NPN transistor, the drive to the base must measure P.

Darlington Configuration:

A Darlington configuration consists of two transistors. The emitter of T1 controls the base of T2, so a very small intensity at the base of T1 controls a much larger current through T2.

Item 7: Lead-Acid Batteries

Features

Mission:

To transform electrical energy received from a generator into electrochemical energy stored inside for later use.

Constitution:

  • Monobloc: A box with separate cells made of polypropylene plates.
  • Cover
  • Elements
  • Electrolyte
  • Separators

Features:

  • Capacity: Determined by the number and dimensions of active plates, the rate of discharge (nominal capacity for a 20-hour discharge), and temperature (capacity decreases in cold conditions).
  • Tension (FEM):
    • Nominal (manufacturer’s specification)
    • Empty (voltage across terminals when not in use)
    • Effective (terminal voltage when connected to an external circuit)
  • Stream Download Quick Frio: The amount of current delivered during a short period.
  • Yield

Working with Batteries

Substitution:

  • Disconnect the negative terminal. Check for corrosion and clean if necessary.
  • Check cables and terminals.
  • Place the new or old battery in its location.
  • Verify polarity. Reversed polarity can damage alternator diodes.
  • Connect the positive (+) terminal first, then the negative (-) terminal.

Check:

A battery works correctly when it has enough energy to power the starter and turn the engine.

Process:

  • Ensure the monobloc is in good condition without cracks.
  • Proper anchoring and securing of terminals to prevent shorts.
  • The electrolyte level covers the plates.
  • Check the state and tension of the alternator belt.

Precautions:

  • Work in a cool, ventilated room.
  • Clean terminals.
  • Check the electrolyte level. In series connections, the total voltage is the sum of individual battery voltages.
  • Avoid connecting batteries with different capacities in series, as the smaller battery will limit the load intensity.
  • Do not connect the charger without plugging it in first. Connect the positive (+) and negative (-) clamps.
  • Do not bring flames near the battery.
  • During charging, remove caps and ensure the temperature does not exceed 50°C.
  • Prevent acid from contacting the charger.
  • Once charged, first disconnect the charger and then disconnect the battery clamps.

Maintenance of Batteries in Service:

  • Keep the cover clean.
  • Check cables and terminals.
  • Apply a layer of petroleum jelly to the terminals to prevent vibration and corrosion.
  • Check the electrolyte level monthly.
  • Avoid making contact between terminals.

Causes That Limit Battery Life:

  • Overload
  • Insufficient load
  • Lack of water