NCP1200 — Current-Mode PWM Controller with Dynamic Self-Supply (DIP-8)

Overview

The NCP1200 (including NCP1200P44, NCP1200P60, and NCP1200P100) is an innovative current-mode PWM controller IC engineered by onsemi for low-power off-line switch-mode power supplies (SMPS) and flyback converters. Housed in a through-hole DIP-8 and surface-mount SOIC-8 package, it revolutionized power supply design with its patented Dynamic Self-Supply (DSS) technology.

By integrating a high-voltage internal startup current source rated up to $500\text{V}$ directly on Pin 8 (HV), the NCP1200 powers itself directly from the rectified high-voltage DC mains bus, completely eliminating the need for an auxiliary transformer winding, auxiliary diode, or bulky dropping resistors. Featuring automatic Skip-Cycle standby mode at light loads (consuming $< 100\text{mW}$ in standby), leading-edge current blanking, and cycle-by-cycle overcurrent protection, the NCP1200 is widely used in AC-DC wall adapters, battery chargers, TV/monitor standby power supplies, smart meter auxiliary power, and SMPS repair projects.

Quick reference


Device Type	Offline Current-Mode SMPS PWM Controller
Package	8-pin DIP (DIP-8 / PDIP-8) / SOIC-8
High-Voltage Startup ( $V_{HV}$ )	$500\text{ V}$ max (Direct Connection to High-Voltage DC Bus)
Internal Operating Voltage ( $V_{CC}$ )	$11.0\text{ V}$ typ (Regulated internally via DSS)
Switching Frequencies	$40\text{ kHz}$ (P44) / $60\text{ kHz}$ (P60) / $100\text{ kHz}$ (P100)
Gate Driver Peak Current	$250\text{ mA}$ source / sink (Direct power MOSFET drive)
Standby Power Optimization	Automatic Skip-Cycle Mode at light loads
Protection Features	Internal Thermal Shutdown, Cycle-by-Cycle Current Limit, Short-Circuit Protection

Pinout (DIP-8 Package)

text

                            ┌───┴───┐
     (Skip Adjust)   Adj   1│ 1    8│ HV (High-Voltage Startup / 500V)
     (Opto Feedback) FB    2│ NCP  7│ NC (High-Voltage Creepage Gap)
     (Current Sense) CS    3│ 1200 6│ VCC (Bypass / Bulk Capacitor)
     (IC Ground)     GND   4│ DIP-8 5│ Drv (MOSFET Gate Drive)
                            └───────┘

Pin	Name	Type	Description
1	`Adj`	Analog Input	Skip cycle peak current level adjust (Leave floating or tie to GND via resistor)
2	`FB`	Feedback Input	Feedback signal input (Connected directly to optocoupler collector)
3	`CS`	Analog Input	Primary current sense input (Connected to source shunt resistor via LEB filter)
4	`GND`	Power	Primary circuit common ground ( $0\text{ V}$ )
5	`Drv`	Output	Totem-pole gate driver output (Drives external high-voltage power MOSFET gate)
6	`VCC`	Power / Bypass	Internal supply rail (Decouple with $10\ \mu\text{F}$ electrolytic / $100\text{nF}$ ceramic)
7	`NC`	No Connect	Omitted pin / No internal connection (Ensures creepage distance from HV pin)
8	`HV`	High Voltage	High-voltage startup pin (Connected directly to rectified $+400\text{V}$ DC bus)

Typical Application Circuit: Isolated Off-Line Flyback Converter (No Aux Winding)

text

    Rectified 85V - 265V AC Mains (+400V DC Bulk Bus)
                 │
                 ├───► Primary Transformer Winding ───► Drain of External MOSFET (e.g. 2SK2645 / FQP6N80)
                 │                                        │
                 ├───► [Pin 8: HV]                        │
                 │        NCP1200P44                      │
                 │     [Pin 5: Drv] ───[ 22Ω - 47Ω ]──────┴── Gate of MOSFET
                 │     [Pin 3: CS]  ───────────────────────── Source Sense Resistor (0.5Ω - 1Ω to GND)
                 │     [Pin 6: VCC] ───[ 10µF Capacitor ]───┐
                 │     [Pin 2: FB]  ───[ PC817 Opto Collector ]
                 │     [Pin 4: GND] ────────────────────────┴── Primary GND (Negative DC Bus)

Frequency Versions Guide

Part Number	Switching Frequency	Typical Application
NCP1200P44 / D40	$40\text{ kHz}$	Lowest EMI, high efficiency in compact adapters
NCP1200P60 / D60	$60\text{ kHz}$	Standard general-purpose flyback supplies
NCP1200P100 / D100	$100\text{ kHz}$	Ultra-compact miniature transformers

Common mistakes

Omitting the VCC bulk capacitor: While the NCP1200 self-supplies from the HV pin, a low-ESR bulk capacitor ( $10\ \mu\text{F} \dots 47\ \mu\text{F}$ ) on Pin 6 (VCC) is mandatory to store energy and maintain $V_{CC}$ ripple within the $9.8\text{V} \dots 11.4\text{V}$ regulation window.
Ignoring thermal dissipation from DSS in high-line continuous operation: Dynamic Self-Supply drops high voltage ( $400\text{V} - 11\text{V}$ ) across an internal linear current regulator. In high-power designs ( $> 15\text{W}$ ), using an optional small auxiliary diode to back-feed VCC from the transformer eliminates DSS continuous power dissipation.

Notes

Suffix Guide: P44 denotes $40\text{kHz}$ in DIP-8 plastic package; D40 denotes $40\text{kHz}$ in SOIC-8 package.