the OB2358, a very popular and cost-effective IC for low-power SMPS (Switch-Mode Power Supplies).

Overview

The OB2358 is a high-performance, low-power, current-mode PWM (Pulse Width Modulation) controller designed for offline AC/DC power supplies. It's manufactured by On-Bright Semiconductor and is a classic example of a "Power Switch" that integrates the PWM controller and a high-voltage MOSFET into a single package (typically in a DIP-8 or SOP-8 package).

This integration significantly simplifies circuit design, reduces component count, saves board space, and improves reliability, making it a go-to choice for applications like:

• Phone/Camera Battery Chargers

• Standby Power for Appliances (Auxiliary Power Supplies - AUX)

• Adaptors for Consumer Electronics (e.g., routers, modems, small gadgets)

• LED Driver Power Supplies

Key Features

1. Highly Integrated: Combines a PWM controller, a high-voltage startup circuit, and a 700V avalanche-rugged power MOSFET all in one chip. This high voltage rating makes it robust against line voltage spikes.

2. Current-Mode Control: Provides inherent line voltage compensation, simplified feedback loop compensation, and superior transient response compared to voltage-mode control.

3. Low Startup Current (< 5µA) and Low Operating Current: This results in very low standby power consumption, often meeting stringent energy efficiency standards like Energy Star or EU ErP Lot 6.

4. Built-in Protections (A key reason for its popularity):

   • Overload Protection (OLP): Protects the circuit if the output is drawing too much power.

   • Over-Voltage Protection (OVP): Shuts down the IC if the output voltage rises abnormally high (e.g., due to a faulty feedback loop).

   • Short-Circuit Protection (SCP): A specific type of overload protection for when the output is shorted.

   • VDD Over-Voltage Protection (VDD OVP): Protects the control IC's power supply pin from voltage surges.

   • Over-Temperature Protection (OTP): Shuts down the chip if its internal temperature exceeds a safe threshold (typically ~160°C).

5. Frequency Dithering: The switching frequency is slightly modulated to spread out the electromagnetic interference (EMI) spectrum, making it easier to pass EMI compliance tests.

6. Auto-Restart Mode: When a fault (like OLP, SCP, OVP) is triggered, the IC enters a low-power "hiccup" mode. It periodically attempts to restart. If the fault is cleared, normal operation resumes automatically. This minimizes power dissipation under fault conditions.