Overview
The NCP1234AD65R2G is a fixed-frequency current-mode controller designed by Onsemi, specifically tailored for flyback converters. This device is part of the NCP1234 family and is pin-to-pin compatible with the previous NCP12xx series. It features Onsemi’s Dynamic Self-Supply (DSS) technology, which simplifies the design of the auxiliary supply and the VCC capacitor by activating an internal startup current source during transients. The controller is optimized for high efficiency in light load conditions and low standby power consumption, making it an excellent choice for cost-sensitive applications.
Key Specifications
| Parameter | Min | Max | Unit | |
|---|---|---|---|---|
| Oscillator Frequency | - | 65 kHz / 100 kHz | - | kHz |
| VCC Operation Range | -0.3 | - | 28 | V |
| Peak Source/Sink Current Drive Capability | - | - | ±500 mA | mA |
| Maximum Duty Cycle | - | - | 80% | % |
| Operating Junction Temperature Range | -40 | - | 150 | °C |
| Storage Temperature Range | -60 | - | 150 | °C |
| Frequency Jittering Amplitude | ±4% | ±6% | ±8% | % |
| Soft-Start Time | - | - | 4.0 ms | ms |
Key Features
- Fixed-Frequency Current-Mode Operation: With built-in ramp compensation to prevent sub-harmonic oscillations.
- Dynamic Self-Supply (DSS): Simplifies the design of the auxiliary supply and VCC capacitor.
- Frequency Foldback and Skip Mode: For maximized performance in light load and standby conditions.
- Timer-Based Overload Protection: With latched (option A) or auto-recovery (option B) operation.
- High-Voltage Current Source: Allows direct connection to high input voltage with brown-out detection.
- Frequency Jittering: For softened EMI signature, active even during frequency foldback.
- Adjustable Overpower Compensation: To keep maximum power independent of input voltage.
- Latch-Off Input: For severe fault conditions, including overtemperature protection using an NTC.
- Clamped Driver Stage: Ensures safe operation with standard MOSFETs.
- Soft-Start: Gradually increases peak current over 4.0 ms to minimize stress on power components.
- Temperature Shutdown: Internally protected against self-overheating.
Applications
- AC-DC Adapters for Notebooks, LCD, and Printers
- Offline Battery Chargers
- Consumer Electronic Power Supplies
- Auxiliary/Housekeeping Power Supplies
Q & A
- What is the primary function of the NCP1234AD65R2G?
The NCP1234AD65R2G is a fixed-frequency current-mode controller designed for flyback converters.
- What is the Dynamic Self-Supply (DSS) feature?
The DSS feature simplifies the design of the auxiliary supply and VCC capacitor by activating an internal startup current source during transients.
- What are the available oscillator frequencies for the NCP1234AD65R2G?
The oscillator frequencies available are 65 kHz and 100 kHz.
- How does the frequency foldback and skip mode work?
The frequency foldback reduces the switching frequency to minimize losses in light load conditions, and the skip mode further reduces switching frequency for extremely low loads.
- What is the purpose of the timer-based overload protection?
The timer-based overload protection detects overloads independently of an auxiliary winding and can operate in either latched or auto-recovery modes.
- How does the high-voltage current source function?
The high-voltage current source allows direct connection to high input voltage and includes brown-out detection and dynamic self-supply.
- What is the effect of frequency jittering on EMI?
Frequency jittering helps to soften the EMI signature by spreading out the energy content of frequency peaks.
- How does the adjustable overpower compensation work?
The adjustable overpower compensation allows the user to adjust the amount of compensation based on the input voltage to maintain maximum power.
- What is the purpose of the latch-off input?
The latch-off input allows the controller to be latched off by either an overvoltage or an overtemperature condition using an NTC.
- What is the soft-start time for the NCP1234AD65R2G?
The soft-start time is 4.0 ms, during which the peak current is gradually increased to minimize stress on power components.
