A syllabus for SMPS (Switch Mode Power Supply) repairing focuses heavily on fundamental electronics, circuit analysis, and systematic troubleshooting. SMPS units are ubiquitous, found in everything from computers (ATX power supplies) to TVs, chargers, LED drivers, and industrial equipment.
Here's a comprehensive syllabus for an SMPS repairing course:
I. Fundamentals of Electronics and Electrical Safety
- Basic Electrical Concepts:
- Voltage, Current, Resistance, Power (Ohm's Law, Watt's Law).
- AC (Alternating Current) and DC (Direct Current).
- Series and Parallel Circuits.
- Capacitive and Inductive Reactance.
- Electronic Components Identification and Testing:
- Passive Components: Resistors (color coding, types), Capacitors (electrolytic, ceramic, film, testing for ESR), Inductors, Transformers (types, testing windings).
- Active Components: Diodes (rectifier, Zener, Schottky, LED), Transistors (BJT, MOSFET, IGBT), Thyristors (SCR, TRIAC - basic understanding), ICs (Integrated Circuits - identification, basic function, reading datasheets).
- Soldering and Desoldering Techniques:
- Types of soldering irons and stations.
- Soldering and desoldering through-hole and SMD (Surface Mount Device) components.
- Using hot air guns for SMD work.
- Proper flux and solder wire selection.
- Importance of clean soldering and desoldering.
- Safety Guidelines for SMPS Repair:
- High voltage hazards and precautions (main filter capacitor discharge).
- Isolation transformer usage.
- Personal Protective Equipment (PPE) - safety glasses, insulated gloves.
- Fire safety.
- ESD (Electrostatic Discharge) precautions.
- Tools and Test Equipment:
- Multimeter: Analog and Digital (for voltage, current, resistance, continuity, diode test).
- Capacitance Meter: For measuring capacitance values.
- ESR Meter: Essential for testing electrolytic capacitors in-circuit.
- Oscilloscope: For analyzing waveforms, checking ripple, and transient behavior (for advanced troubleshooting).
- Light Bulb Trick (Series Bulb Tester): A crucial safety and diagnostic tool.
- Variable AC power supply (Variac).
- Bench power supply (for testing low voltage sections).
- Component testers (e.g., transistor tester).
- Circuit diagrams and service manuals.
II. Introduction to SMPS Technology
- What is an SMPS?
- Definition and purpose.
- Advantages over Linear Power Supplies (efficiency, size, weight).
- Applications of SMPS (computers, TVs, chargers, LEDs, industrial electronics).
- Block Diagram of a Typical SMPS:
- Understanding the main sections: Input Rectification & Filtering, Switching Stage, High-Frequency Transformer, Output Rectification & Filtering, Feedback Loop, Control Circuit (PWM IC).
- SMPS Topologies (Basic Understanding):
- Flyback converter.
- Forward converter.
- Buck converter.
- Boost converter.
- (More advanced: Buck-Boost, SEPIC, Push-Pull, Half-Bridge, Full-Bridge if covered).
- Working Principle of Each Section:
- Input Stage: EMI filter, bridge rectifier, bulk filter capacitor.
- Switching Stage: Power MOSFET/Transistor, PWM (Pulse Width Modulation) control.
- High-Frequency Transformer: Energy transfer and isolation.
- Output Stage: Output rectifier diodes (Schottky often used), output filter capacitors, output inductors.
- Feedback Loop: Optocoupler, error amplifier (TL431 often used), voltage divider.
- Control IC (PWM Controller): Startup circuit, oscillator, driver, protection features.
- Protection Circuits: Over-voltage protection (OVP), Under-voltage protection (UVP), Over-current protection (OCP), Short-circuit protection (SCP), Over-temperature protection (OTP).
- Power Factor Correction (PFC): Passive and Active PFC (basic concepts, importance).
III. Common SMPS Faults and Troubleshooting Techniques
- Understanding Failure Modes:
- No power / Dead unit.
- Low output voltage.
- High output voltage.
- Intermittent power / Power cycling / Blinking.
- Power shutdown.
- Overheating components.
- Noise or hum.
- Systematic Troubleshooting Approach:
- Visual Inspection: Burnt components, bulged capacitors, cold solder joints, cracks on PCB.
- Fuse Check: If fuse is blown, identify root cause (short circuit).
- Voltage Measurements:
- Primary DC bus voltage.
- Control IC VCC.
- Output voltages.
- Waveform analysis with oscilloscope (PWM signal, output ripple).
- Component Testing:
- In-circuit and out-of-circuit testing of diodes, transistors, capacitors (especially ESR).
- Testing optocouplers.
- "Hot" vs. "Cold" Side Troubleshooting: Understanding the isolation barrier.
- Common Faults and Their Causes:
- Bulged/Leaky Capacitors: Primary and secondary filter capacitors are common failure points.
- Shorted Switching MOSFET/Transistor: Often caused by faulty control IC or excessive load.
- Faulty Control IC: No PWM signal, incorrect VCC.
- Shorted Output Diodes: Causes overload and shutdown.
- Open Resistors: Especially startup resistors or sensing resistors.
- Faulty Optocoupler/TL431: Disrupts feedback loop, leading to high or low output.
- Faulty Transformer: Rare, but can cause no output.
- Open Circuit in Feedback Loop: Leads to unregulated high voltage.
- Load Issues: Short circuit or excessive load on the output can cause SMPS shutdown.
- Practical Troubleshooting Methods:
- The "Series Light Bulb Trick" for safely testing short circuits.
- Using the ESR meter to quickly identify bad capacitors.
- Methods to discharge the main capacitor safely.
- Techniques for isolating faulty sections (e.g., removing secondary diodes to test primary).
- Troubleshooting without schematics.
IV. Specific SMPS Applications and Repair
- ATX Power Supply Repair:
- Understanding ATX connectors and voltage rails (+12V, +5V, +3.3V, -12V, +5VSB, Power Good, PS_ON).
- Common ATX SMPS faults and their diagnosis.
- Testing ATX power supplies (load testing, paperclip test).
- LED TV/LCD Monitor SMPS Repair:
- Understanding integrated power boards (SMPS + LED Driver/Inverter).
- Common failures in TV power supplies.
- Backlight driver issues related to SMPS.
- Laptop Charger/Adapter Repair (External SMPS):
- Common issues (cable breaks, component failure).
- Other Common SMPS (e.g., printer, router, CCTV camera power supply repair):
- Applying learned principles to various SMPS types.
V. Replacement and Component Sourcing
- Finding Equivalent Components:
- Understanding component specifications (voltage, current, power, frequency, ESR).
- Using datasheets and cross-reference guides.
- Best Practices for Component Replacement:
- Using quality replacement parts.
- Ensuring proper heatsinking.
- Importance of low ESR capacitors.
- Heat Management:
- Understanding heat dissipation.
- Using thermal paste and heat sinks.
Practical Sessions (Crucial for an SMPS Repair Course):
- Hands-on disassembly and assembly of various SMPS units (ATX, TV, adapters).
- Extensive practice with multimeter, ESR meter, and oscilloscope for component testing and circuit analysis.
- Identifying and replacing faulty components on actual SMPS boards.
- Diagnosing and repairing common SMPS faults (e.g., dead unit, low voltage, blinking).
- Practicing safety procedures during live testing.
- Using the series bulb tester to diagnose shorts.
- Performing load tests on repaired SMPS units.
