🎬 Electronics Is Science — And I Teach It That Way

Hello, I’m Lewis Loflin — and this is not an Arduino tutorial. This is science.

Electronics is a form of applied physics. That means real currents, real voltages, and real charge movement — not abstractions.

What you're about to see isn’t another plug-and-play tutorial. This is real electronics — grounded in testable, material science.

I treat electronics as what it is: applied physics.

I do not — and will not — teach positive current flow as a valid model. Why? Because it fails to explain:

• Early radio and TV systems
• Vacuum tubes and CRT behavior
• Gas discharge and plasma devices
• Electroplating and battery chemistry
• Industrial electrolytic processes
• Aluminum smelting and fuel cells
• Ion propulsion systems used in space

In this series, you’ll see working physical examples: lab-built circuits, ion beam demonstrations, and working models of devices that depend on actual electron and ion movement.

If you're tired of plug-and-play fluff and want real science that explains the real world — you're in the right place.

⚠️ Lesson 3: The Problem with "Conventional Current"

Conventional current is the idea that electric current flows from positive to negative.

This model dates back to the 1700s — before electrons were discovered. Scientists like Benjamin Franklin assumed charge flowed from the positive terminal. That convention stuck, even after we learned the truth.

In reality:

• Electrons are the actual moving charge carriers
• They flow from negative to positive
• This is called electron flow

🔍 Why Conventional Current Is Misleading

• In vacuum tubes, only electrons move across empty space
• In batteries, electrons leave the negative terminal and return via the load
• In electroplating, metal builds up at the negative electrode due to incoming electrons
• In ion propulsion systems, particles are physically accelerated by electric fields based on real polarity

Electron flow matches the direction of physical charge movement — not just theory or diagram arrows.

That’s why in this series, we use electron flow only. It matches the science — and the hardware.

💡 Lesson 4: Plasma, Ion Bombardment, and Tube Aging

Gas discharge tubes — from Crookes tubes to fluorescent lights — rely on plasma: a mixture of free electrons and positive gas ions formed in a low-pressure gas under high voltage.

Electrons move to the anode (+), and positive ions accelerate toward the cathode (−). But those ions don’t just hit and stop — they collide with real force, damaging the electrode surface.

⚠️ Cathode Bombardment Causes Wear

• Sputtering: Positive ions knock atoms off the cathode surface
• Material loss: Over time, the electrode erodes
• Gas contamination: Ejected atoms mix into the gas and affect performance

In my Crookes tube experiment, I observed this directly — the copper target developed a visible pit from ion impact.

📉 Real-world examples of wear:

• ⚡ Fluorescent lamps: Ends blacken as electrode material is lost
• ⚡ Neon signs: Brightness fades due to cathode wear
• ⚡ Xenon flash tubes: Lifetime is limited by electrode erosion

This isn’t theoretical. This is **measurable, physical damage** — caused by charged particles slamming into metal at high energy.

Plasma is powerful, but it comes at a cost. Every flash and glow leaves a mark.

Edison Science Center Fluorescent-Light

💡 How Fluorescent Lamps Work – A More Accurate Explanation

Fluorescent lamps use a low-pressure mercury vapor arc discharge to produce ultraviolet (UV) light, which then excites a phosphor coating on the inside of the tube to emit visible light.

1. 🔌 The Role of the Ballast

• In magnetic systems, the ballast is a choke (inductor) that limits current through the lamp once the arc is established.
• In electronic ballasts, high-frequency AC is used and startup is more precisely controlled — often with voltage spikes or programmed preheating.

2. ⚡ Starting the Arc

• The lamp initially contains a small amount of argon gas and mercury vapor. At power-on, the gas is not yet conductive.
• To start conduction, the electrodes (cathodes) are either preheated (preheat/rapid start) or a high-voltage spike is applied (instant start).
• Once enough free electrons are present, the gas becomes ionized and forms a conductive plasma — the “arc.”

3. 🧊 Cold Temperature Effects

At low temperatures, ionization is harder due to lower atomic energy levels and fewer free electrons. More voltage is needed to start the lamp. Preheating the electrodes helps overcome this.

4. ⚠️ Current Limiting Is Critical

Once the arc is formed, plasma has very low resistance. If not limited, the current would increase rapidly and destroy the lamp. That’s why all discharge lamps require a current-limiting ballast — to stabilize operation.

✅ Common Starting Methods:

• Preheat: Filaments warm up before starting — uses a starter switch.
• Rapid Start: Filaments warm continuously and arc starts smoothly.
• Instant Start: No preheat, high voltage strikes arc immediately — less gentle on the cathodes.
• Programmed Start: Controlled preheat and strike timing — common in modern electronic ballasts.

💡 How a Fluorescent Lamp Ballast Works

A fluorescent lamp ballast serves two essential functions:

⚡ 1. Starting the Lamp (High-Voltage Ionization)

• The gas inside the lamp is non-conductive until ionized.
• The ballast delivers a high-voltage spike (typically 400–700 V) to strike the arc.
• In magnetic systems, this spike comes from a after the starter opens.
• In electronic ballasts, a high-frequency driver applies the necessary voltage automatically.

🔌 2. Limiting Current After Ignition

• Once ionized, the plasma conducts easily — internal resistance drops sharply.
• The ballast limits current to a safe level to prevent tube damage.
• Magnetic ballasts use an inductor (choke) in series with the tube.
• Electronic ballasts regulate current precisely with high-frequency switching.

💭 Why This Matters:

Without a ballast, the lamp would either not start — or self-destruct due to uncontrolled current. The ballast ensures both safe ignition and stable operation.

Note: Ionization of low-pressure gas is not automatic — it requires sufficient voltage to begin conduction, just like in a neon sign or Crookes tube.

Fluorescent Lamp Starter: What the Capacitor Does

In a classic preheat fluorescent circuit (choke ballast + glow-bottle starter), the small capacitor inside the starter is wired across the starter’s contacts. It acts as a snubber: reduces contact arcing and suppresses radio-frequency noise. It is not the same as the large power-factor correction capacitor sometimes found across the mains in fixtures.

Why the Capacitor Is There

• Extend contact life: When the starter opens, the ballast (an inductor) tries to keep current flowing, creating a high dv/dt spike. The capacitor momentarily absorbs energy, reducing arcing and metal transfer on the contacts.
• Suppress RFI/EMI: The same spike produces broadband radio noise (“clicks” on AM/FM). The capacitor shunts the high-frequency component, reducing radio interference.

Typical Values & Notes

• Cap value (starter snubber): typically a few nF (e.g., ~4.7–10 nF), high pulse rating.
• Safety rating: Because it’s effectively across a switching mains path, use a safety-rated capacitor (e.g., interference-suppression type, X2-class or a manufacturer-approved starter component).
• Don’t confuse with PF cap: Many fixtures also have a separate, larger capacitor across the mains for power factor correction; that one is not inside the starter and serves a different purpose.

How the Preheat Starter Works (Quick Sequence)

1. Glow & close: Mains across the starter makes the neon glow and heat a bimetal strip → contacts close.
2. Preheat: With contacts closed, current flows through the filaments via the ballast, heating cathodes.
3. Open & kick: The bimetal cools/open; the ballast’s inductive “kick” raises voltage across the tube, striking the arc.
4. Run: Lamp conducts; voltage across starter falls so it stays open. The snubber cap has done its job at the open instant.

Safety

This circuit operates at mains voltage. Use proper isolation, discharge capacitors before handling, and only service with appropriate skills and safety gear.

📦 Selenium High-Voltage Diode Reference

This reference compares three common selenium HV rectifiers used in CRT televisions and high-voltage circuits. These devices are low-current, high-voltage rectifiers — not to be confused with silicon power diodes.

Reminder: These are not high-current devices. Despite the high voltage, low current (under 2mA) for CRT anodes.

🔬 Abundance of Semiconductor Elements in Earth's Crust

Note: ppm = parts per million by weight. These values are approximate averages and may vary by source.

🔍 Clarifying Abundance: Arsenic and Germanium

🧪 Arsenic (As)

• Abundance: ~1.8 ppm in Earth’s crust — similar to tin and zinc.
• Source: Found in arsenide ores like arsenopyrite; recovered during metal smelting.
• Semiconductor Use: Gallium arsenide (GaAs) for high-frequency ICs, LEDs, laser diodes, and solar cells.
• Status: Not rare — widely available and inexpensive.

🧪 Germanium (Ge)

• Abundance: ~1.5 ppm — more common than many assume.
• Source: Byproduct of zinc and copper smelting; also found in coal and fly ash.
• Semiconductor Use: High-speed transistors, fiber optics, IR optics, and space-grade solar cells.
• Status: Not rare, but considered strategic due to limited direct mining.

⚖️ Comparison Table

✅ Conclusion: Arsenic is not rare at all, and germanium — while less abundant — is still far more available than many specialized semiconductor materials like indium and tellurium.

Selenium rectifier compared to vacuum tube rectifier.

🧲 Selenium Rectifier – Construction and Process

Selenium rectifiers do not use doped PN junctions like modern silicon or germanium diodes. Instead, they operate using a metal–semiconductor junction with a naturally formed barrier oxide layer. The result is a one-way conduction effect similar to a diode, but achieved through different means.

🔧 Basic Construction:

• Base Metal Plate: Usually aluminum or steel; acts as the anode.
• Selenium Layer: Thin crystalline selenium deposited on the base metal; acts as a semiconductor.
• Oxide Layer: A thin layer of selenium dioxide (SeO₂) forms naturally or through heating, creating the rectifying barrier.
• Top Contact: A metal layer (typically nickel or cadmium); serves as the cathode.
• Stacked Construction: Multiple cells are stacked for higher voltage handling, often with cooling fins.

⚡ How It Works (Rectification):

• Electrons flow easily forward from the cathode into the selenium layer and out through the base plate (anode) to the rest of the circuit.
• In reverse, the selenium dioxide layer blocks electron flow, providing rectification.
• This is a metal–semiconductor junction process — similar to a Schottky diode, not a PN junction.

🧪 Key Characteristics:

📚 Why Selenium Rectifiers Use Stacking

Selenium rectifiers are built from multiple thin metal–selenium cells stacked in series. This design is not just mechanical — it improves the electrical performance in several ways:

• Higher Reverse Voltage Handling: Each selenium cell can withstand only a limited reverse voltage before leakage becomes significant. Stacking cells in series increases the total reverse voltage rating, as each cell shares part of the voltage.
• Lower Leakage Current: With more cells sharing the reverse voltage, each one operates at a lower voltage stress, which reduces leakage and improves overall rectification.
• Higher Power Dissipation: Each cell has a limited current capacity and heat dissipation ability. Adding more cells increases total surface area for heat transfer, allowing the rectifier to handle higher load currents without overheating.

Many stacks also include cooling fins or air gaps between plates to improve heat dissipation during high-load operation.

🏁 Summary

Selenium rectifiers operate through a metal–semiconductor junction with a critical oxide layer (SeO₂), not by PN junctions. Though largely obsolete today, they played an essential role in early power electronics before being replaced by silicon diodes.

⚙️ Selenium in Electronics

Selenium (Se) is a nonmetallic element with semiconducting properties, historically used in:

• Selenium Rectifiers: Convert AC to DC using a metal–semiconductor junction and a thin selenium dioxide barrier layer. Common in vintage power supplies before silicon diodes.
• Selenium Photocells: Early solar cells operating by the photovoltaic effect. Used in light meters and educational kits. No PN junction — relies on photoexcitation within crystalline selenium.

Though largely obsolete today, selenium devices were durable and important milestones in early semiconductor development.

🌍 Selenium – Abundance and Availability

📊 Natural Abundance

• Earth’s crust: ~0.05 parts per million (ppm)
• Comparison with other elements:
  • Silicon: ~282,000 ppm
  • Copper: ~60 ppm
  • Tellurium: ~0.001 ppm
• Selenium is more common than tellurium, indium, and some rare earths, but far less abundant than industrial metals like iron or aluminum.

🏭 Industrial Sources

• Selenium is not mined directly — it is typically recovered as a byproduct of copper refining, especially from anode slimes during electrolytic processing.
• Also obtained in smaller quantities from nickel and lead refining.

🌐 Global Supply and Uses

• Annual production: Approximately 3,000–5,000 metric tons worldwide.
• Top producers: Japan, Canada, Germany, Peru, and the United States.
• Main applications:
  • Glass manufacturing (decolorizing and tinting)
  • Metallurgy (steel alloying)
  • Electronics (rectifiers, solar research)
  • Agriculture (as a trace element in animal feed)

📦 Strategic Considerations

• Selenium is not classified as a critical or rare element in most global assessments.
• However, its availability is closely tied to copper production, which may limit supply if demand increases in electronics or solar technology.

🔆 Selenium Photocells – Construction and Operation

Selenium photocells — also known as selenium solar cells or barrier-layer photodiodes — convert light into electricity using a metal–semiconductor junction. Unlike silicon solar cells that use a doped PN junction, selenium cells depend on the natural photoelectric properties of selenium.

🔧 Construction:

• Metal Base Plate (Anode): Usually iron, aluminum, or brass — serves as mechanical support and electrical contact.
• Selenium Layer: A thin, crystalline layer of selenium vapor-deposited on the base — acts as the photosensitive semiconductor.
• Oxide Barrier Layer: A naturally formed layer of selenium dioxide (SeO₂), key to rectifying and photoresponse behavior.
• Transparent Conductive Layer (Cathode): Often a thin film of gold, platinum, or tin oxide applied in a grid or semi-transparent coating to allow light in while collecting charge carriers.
• Protective Coating: A clear glass or plastic cover protects the cell and may serve as a light diffuser or lens.

🌞 How It Works:

When light strikes the selenium layer, it excites electrons into the conduction band. These photo-generated carriers are separated by the internal barrier layer (SeO₂), producing a voltage across the cell. The result is a small direct current when connected to a load.

• No external power source is needed.
• The cell operates in — converting light directly to electrical energy.
• Typical output: ~0.5V open-circuit per cell with very low current (a few μA to mA).

⚙️ Characteristics:

📸 Common Applications (Historical):

• Light meters in vintage cameras (Weston-style meters)
• Exposure meters
• Solar demonstration kits in the 1950s–70s
• Early solar-powered toys and novelty gadgets

🧪 Summary:

Selenium photocells are barrier-layer photovoltaic devices that predate silicon solar cells. Though inefficient by modern standards, they were widely used for decades due to their simplicity and reliability. Their construction is more closely related to selenium rectifiers than to modern PV cells.

⚠️ Negative Differential Resistance (NDR) ≠ Negative Resistance

Negative Differential Resistance occurs when, over a specific range of voltages, increasing the voltage causes the current to decrease. This behavior appears in nonlinear devices and is different from the idea of a component having a fixed "negative resistance."

📉 What It Means:

• In normal resistors: voltage ↑ → current ↑ (positive slope)
• In NDR regions: voltage ↑ → current ↓ (negative slope)

🧪 Devices That Exhibit NDR:

• 🔹 Tunnel diodes: Peak current followed by a valley as voltage increases
• 🔹 Neon lamps: After ionization, voltage drops as current increases
• 🔹 Gas discharge tubes: Similar to neon lamps, used in oscillators
• 🔹 Gunn diodes: Used in microwave RF applications

📘 Important Distinction:

This is not true “negative resistance” like a power source. It’s a local, nonlinear behavior — a negative differential resistance over part of the V–I curve, not the whole device.

💬 Analogy:

Imagine pushing a cart: normally, more force = more speed. But at a certain point, adding more force slows it down. That’s how NDR works — only over a specific range.

Note: This effect is real, measurable, and used in practical circuits like oscillators and voltage regulators.

🔌 Understanding “Negative Resistance” – A Technician’s Guide

❓What Is “Negative Resistance”?

Despite the name, negative resistance doesn’t mean a resistor with a negative value. Instead, it's a way to describe a device that behaves differently under certain conditions—as current increases, the voltage across it goes down.

🧠 Think of Resistance Normally:

Ohm’s Law:
V = I × R
More current → more voltage drop.
That’s positive resistance (like a resistor, heater, wire).

📉 So What’s “Negative” Resistance Then?

It’s about the slope of a voltage–current graph:

• In some devices, you increase current but the voltage drops
• The slope (ΔV / ΔI) becomes negative
• This region is called a Negative Resistance Region

⚙️ Real-World Devices That Show This:

📈 Visual Example (simplified):

Voltage (V)
  |
  |       /\
  |      /  \
  |     /    \_________
  |    /               \
  |___/                 \____> Current (I)
       ↑
   Negative resistance region (slope ↓)
  

In this middle section, more current actually causes voltage to drop. That’s what we call negative resistance.

🧰 Why It Matters

These devices are used in oscillators, flashing lights, trigger circuits, and microwave systems. They can self-oscillate or sustain pulses, useful in timing or signal generation.

✅ Technician-Friendly Takeaway:

• It’s not magic, and it’s not a “negative resistor.”
• It just means the device acts differently in a certain region.
• Think of it as reverse behavior: more current, less voltage.