PTC Thermistors for Energy-Saving Lamps and Ballasts

PTC thermistors are primarily used in energy-saving lamps and electronic ballasts for the “preheat soft start” function, significantly improving lamp life and energy efficiency. The following are their core applications and technical highlights:
TÔI. Operating Principle

Cold, Low-Resistance Phase
When the circuit is started, the PTC is at room temperature and has a low resistance (e.g., 30-60Ồ). Current flows through the PTC to preheat the filament (typically taking 0.4-2 seconds to reach an operating temperature of 1160K), preventing direct high-voltage shock from causing sputtering and filament loss.

Hot, High-Resistance Phase
When the PTC temperature reaches the Curie point (e.g., 75°C-105°C), its resistance suddenly increases (to several thousand ohms). Current is diverted to the resonant circuit, generating high voltage to ignite the lamp, completing the soft start process.

Circuit design of PTC thermistors for energy-saving lamps and ballasts

Ii. Core Advantages
Extended Lamp Life: Preheat start increases lamp life by 4-5 lần.
Reduced Electrical Stress: Reduces the impact of sudden high voltage on electronic components.
Self-Recovery: Automatically resets after the fault is resolved, eliminating the need for replacement.

Iii. Selection parameters and model examples

Application Diagram

As shown in the figure: When the circuit is initially connected, Rt is at room temperature, its resistance far lower than that of C2. Current flows through C1, and Rt forms a circuit to preheat the filament. After approximately 0.4-2 giây, Rt’s temperature exceeds the switch temperature, Tsw, and enters a high-resistance state. Its resistance is much higher than the impedance of C2. Current flowing through C1 and C2 forms a loop, causing LC resonance and generating high voltage, which illuminates the lamp.

Common Models:
MZ4/MZ5: Suitable for small and medium-power CFLs (18W-72W).
WMZ11A: Dedicated for high-power ballasts, with a withstand voltage of ≥220V.

Iv. Typical Application Circuit
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+Power Supply → C1 → PTC (Rt) → Filament → C2 → Resonant Circuit → High-Voltage Output

C1/C2: Coupling capacitors, working with the PTC to control preheating time.

V.. Cost and Market
Price Range: 0.06-1.5 yuan/unit (depending on model and purchase quantity).
Mainstream Brands: Minzheng, Sanbao, vân vân., supplying international manufacturers such as Philips and GE.

Through appropriate selection, PTC thermistors can effectively solve the startup reliability issues of CFLs/ballasts and are key components in the energy-saving lighting industry.

Model List