1W MONO POWER AMP# Technical Documentation: FAN7023MX High-Voltage Current-Mode PWM Controller
Manufacturer : FAI (Fairchild Semiconductor / ON Semiconductor product family)
Component Type : High-Voltage Current-Mode PWM Controller IC
Primary Application : Offline Switch-Mode Power Supplies (SMPS)
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## 1. Application Scenarios
### Typical Use Cases
The FAN7023MX is specifically engineered for offline power conversion in low-to-mid power applications. Its integrated high-voltage startup and current-mode control architecture make it suitable for building compact, efficient, and cost-effective AC-DC converters.
* Primary Use : As the core controller in Flyback Converter topologies. This is its most common implementation, providing isolated DC output from a universal AC mains input (85VAC to 265VAC).
* Secondary Use : In non-isolated Buck or Buck-Boost configurations for auxiliary power rails or LED driver circuits, though less frequent than flyback.
### Industry Applications
This IC is prevalent in industries requiring reliable, low-component-count power solutions:
* Consumer Electronics : Power adapters/chargers for routers, set-top boxes, monitors, and small appliances.
* Industrial Controls : Auxiliary power supplies for PLCs, sensors, and motor drives.
* Computer Peripherals : External power supplies for printers, scanners, and external hard drives.
* LED Lighting : Low-to-medium power LED driver modules, particularly where power factor correction (PFC) is not a strict requirement.
### Practical Advantages and Limitations
Advantages:
* Integrated High-Voltage Startup : The built-in HV startup circuit connects directly to the rectified high-voltage DC bus, eliminating the need for an external startup resistor and reducing standby power consumption.
* Low System Cost : Minimal external component count due to integrated features (startup, oscillator, protection).
* Current-Mode Control : Provides inherent cycle-by-cycle current limiting, simplified feedback loop compensation, and faster transient response compared to voltage-mode control.
* Comprehensive Protection Suite : Typically includes Overload Protection (OLP), Over-Voltage Protection (OVP), and Over-Temperature Protection (OTP) , enhancing system robustness.
* Frequency Jittering : Many variants incorporate frequency jitter to reduce peak electromagnetic interference (EMI), easing filter design.
Limitations:
* Limited Power Range : Optimized for applications below approximately 75W. For higher power levels, a dedicated PFC front-end or a more robust controller is recommended.
* Fixed Operating Frequency : The FAN7023MX typically operates at a fixed frequency (e.g., 65 kHz), limiting flexibility for designs requiring frequency modulation for efficiency optimization or noise reduction.
* No Integrated PFC : Lacks active Power Factor Correction. For applications requiring high PF (e.g., >0.9 for compliance with standards like ENERGY STAR or EU CoC), an additional PFC controller stage is necessary.
* Heat Dissipation : While it includes OTP, the SOIC-8 package has limited thermal dissipation capability. Careful PCB layout for thermal management is critical in high-ambient-temperature environments.
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## 2. Design Considerations
### Common Design Pitfalls and Solutions
1. Pitfall: Transformer Saturation or Excessive Ringing.
* Cause : Improper design of the current sense network (Rcs and Ccs) or poor transformer specification (insufficient margin for peak current).
* Solution : Precisely calculate the current sense resistor (`Rcs`) value based on the controller's internal current limit threshold (e.g., `Vcs_limit`). Use the recommended RC filter (`Rcs`, `Ccs`) at the CS pin to filter
