MS1007SH

Application Note


Overview/Features

The MS1007SH quasi-resonant circuit to reduce standby power, achieve high efficiency and low noise.
The IC incorporate various functions to make it more user-friendly and to make it easier to design a power supply with fewer external components.

1.　Quasi-resonant design for high efficiency and low noise.
2.　Four-Step soft-start function.
3.　Onboard startup circuit requires no startup resistor, dramatically reducing losses in the startup circuit.
4.　The automatic bottom skip function controls increases in oscillation frequency and improves efficiency under light loads.
5.　Auto burst function improves efficiency under light loads with no additional components.
6.　Soft drive circuit reduces noise.
7.　Thermal shutdown, overvoltage protection, and overload protection. (Auto-retry mode)
8.　Primary current limit circuit incorporates an input voltage dependence correction circuit to reduce the number of components required.
9.　Bias assist function for startup circuit.
10. VCC-GND short circuit protection function.
11. SOP-8/7J package employed for compact dimensions.


Application Note Contents

1. Overview
    1.1 Introduction
    1.2 Characteristics
    1.3 Applications
    1.4 Appearance and dimensions
    1.5 Basic circuit configuration
2. Block diagram
    2.1 Block diagram
    2.2 Pin names
3. Circuit operation
    3.1 Startup
        3.1.1 Startup circuit
        3.1.2 Soft-start (SS)
        3.1.3 Bias assist
    3.2 Oscillation
        3.2.1 On-trigger circuit
        3.2.2 Quasi-resonance
        3.2.3 Soft drive
        3.2.4 Bottom skip operation
        3.2.5 Output voltage control
    3.3 Burst operation mode
        3.3.1 Auto-burst mode (Auto-Standby mode)
    3.4 Protection mode
        3.4.1 VCC overvoltage protection OVP (Auto recovery mode)
        3.4.2 Overcurrent protection (OCP)
        3.4.3 Overload protection (Auto recovery mode)
        3.4.4 VCC-GND short circuit protection
        3.4.5 Leading edge blank (LEB)
        3.4.6 On-trigger malfunction prevention circuit (Tondead)
        3.4.7 Thermal shutdown (TSD) (Auto recovery mode)
4. Pin functions
    4.1 Z/C pin
    4.2 F/B pin
    4.3 GND pin
    4.4 OCL pin
    4.5 VG pin
    4.6 VCC pin
    4.7 Vin pin
5. Design procedure
    5.1 Design flow chart
    5.2 Example of main transformer design
    5.3 Formulas for main transformer design
    5.4 Checking the operating points
        5.4.1 Variables in formulas
        5.4.2 Bottom skip start power
        5.4.3 Bottom skip end power
        5.4.4 Auto-burst start/end power
        5.4.5 Drooping point power
    5.5 Pin design
        5.5.1 Z/C pin (Pin 5)
        5.5.2 F/B pin (Pin 6)
        5.5.3 OCL pin (Pin 2)
        5.5.4 VG pin (Pin 1)
        5.5.5 VCC pin (Pin 3)
        5.5.6 Setting resonating capacitor

Example Circuits


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