Diodes 10w Ap3928 Ev1 Ac Voltage Input Step-down Regulator User Guide

10W AP3928 EV1 User Guide
EVB User Guide

Chapter 1. Introduction

General Description

AP3928 is an off-line universal AC Voltage input step-down regulator which provides accurate constant voltage (CV) output, outstanding low standby power, high efficiency at light loading, and excellent dynamic response based on non-isolated buck topology.
The AP3928 EV1 Evaluation Board provides a good design example for a cost-effective 9.9W single output 18V/550mA power application used in home appliances.

AP3928 Key Features

• Universal 85V to 265V VAC Input
• Internal MOSFET 700V (6.5Ω max)
• Maximum 600mA rated Output current
• Low Standby Power Consumption (<30mW at no load)
• High Light-Loading and Average efficiency can meet DOE and CoC requirement
• Frequency Modulation to suppress EMI to meet EN55022 class B
• Rich Protection including OTP, OLP, OLD, SCP
• Extremely low system component count
• Totally Lead-free & Fully RoHS Compliant (SO-8)
• Halogen and Antimony Free. “Green” Device

Applications

• Non-Isolated Home Appliances: AC Fans, Rice Cookers, Air conditioners, Coffee Machines, Soy Milk Machines, etc.
• Auxiliary Power for IoT Devices.

Board Pictures

Chapter 2. Power Supply Specification

System Performance

The system performance contains input/output characters, specifications, EMC, protections, etc.

Environment

Chapter 3. Schematic and Bill of Material

Schematic

Bill of Material

Table 1: Bill of Material

Chapter 4. The Evaluation Board Connections

PCB Layout

Circuit Description

4.2.1 Input EMI Filtering
The input stage is composed of fusible resistor F1, rectifier bridge DB1, filtering inductor L1, Capacitors C1 and C2. Resistor F1 is a flame-proof, fusible, wire-wound resistor. It limits inrush current to safe levels for input rectifier diodes, provides differential mode noise reduction and acts as an input fuse in the event of a short circuit.
4.2.2 Control IC
AP3928 co-packages a 700V power MOSFET and control circuitry into a cost-effective SO-8 package. The device is self-starting from the Drain pin with local supply decoupling provided by a small capacitor C3 (at least 100nF) connected to the BP pin when AC source is applied.
4.2.3 Output Rectification
During the ON time of U1, current ramps in L2 and is simultaneously delivered to the load. During the OFF time the inductor current ramps down via the free-wheeling diode D3, feedback diode D1, and the load. Diode D3 should be ultra-fast diodes (Trr<50ns or lower). Capacitor C3 should be selected to have an adequate ripple margin (low ESR type).
4.2.4 Output Feedback
The voltage across L2 is rectified by C4 and D1 during the off-time of U1. For forwarding voltage drop of D1 and D3 is approximately equal, the voltage across C4 tracks the output voltage. To provide a feedback signal, the voltage across C4 is divided by R1 and R2//R3. This voltage is specified for U1 at FB pin (2.5V). This allows the simple feedback to meet the required overall output tolerance of ±5% at rated output current.
4.3 Quick Start Guide

1. The evaluation board is preset at 18V/550mA from the output.
2. Ensure that the AC source is switched OFF or disconnected before doing connection.
3. Connect the AC line wires of the power supply to “L” & “N” connectors on the left side of the board.
4. Turn on the AC main switch.
5. Measure “+V” & “GND” connectors to ensure correct output voltage, 18V.

CAUTION: This EV board is non-isolated. Do not touch anywhere there are electrical connections because they are all coupled to a high voltage potential.

Chapter 5. System Test

Input & Output Characteristics

5.1.1 Input Standby Power
Standby power and the output voltage is measured after 10-minute aging. The voltage data is tested at the PCB terminal. All data is tested at ambient temperature.
Table 2: Standby Power and Output Voltage @ no load

5.1.2 Efficiency
The efficiency data is measured after 10-minute aging, and it is tested at the PCB terminal. All the data is tested at ambient temperature.
Table 3: Conversion Efficiency

5.1.3 Line and Load Regulation
The line and load regulation data is measured after 10-minute aging. The voltage data is tested at the PCB terminal. All the data is tested at ambient temperature.
Table 4: Line and Load Regulation Data

Key Performance Test

5.2.1 Start-up Performance
The start-up time is measured with a differential probe across AC inputs, “L” and “N” connectors, and a common low-voltage probe across output terminals, “+V” and “GND” connectors. Before starting up, buck capacitors should be discharged.
Table 5: Start-up Performance

CH2:Vin; CH4:Vo

5.2.2 Rise Time
The rise time is measured with a common low-voltage probe across output terminals, “+V” and “GND” connectors. Before starting up, output capacitors should be discharged.
Table 6: Rise Time

5.2.3 Voltage Stress
The voltage is measured between the “Drain” and “S” pins of AP3928. The test needs differential probes.
Table 7: Internal MOSFET Drain-Source Voltage Stress

5.2.4 Output Ripple & Noise
The ripple and noise is tested at PCB terminal, using a 10:1 probe without probe cap and ground clip. The bandwidth is limited to 20MHz. A 10µF electrolytic capacitor and a 100nF ceramic capacitor should be paralleled to the output terminal.
Table 8: Ripple & Noise

5.2.5 Dynamic Response
The dynamic response of output voltage is tested at the PCB terminal and the bandwidth is limited to 20MHz. Loading is set 0A as low load and 550mA as high load. Besides, the period is 2 seconds and the ramp is set at 250mA/µs.
Table 9: Dynamic Response

Protection Test

5.3.1 Short Circuit Protection (SCP) Test
The SCP test is measured under the condition that output cable terminals are shorted. The cable end short resistance value used is 50mΩ.
Table 10: Short Circuit Protection Test

5.3.2 Open Loop Detection (OLD) Protection Test
The open-loop detection protection is measured when FB pin is connected to the Source pin.
Table 11: Open Loop Detection Test

5.3.3 Overload Protection (OLP) Test
The overload protection point is tested as below: increase the loading by 10mA/step until the system cannot maintain a stable output, and then mark the loading level as overload protection point.
Table 12: Overload Protection Point test

Thermal Test

The thermal test is under ambient temperature after 1-hour aging. The board has no case in open frame. The thermal imager is used to observe the surface temperature of AP3928.

System EMI Scan

The power supply meets EN55022 Class B (for 110Vac input and 230Vac input) EMI requirements with more than 6dB margin.
5.5.1 Conducted EMI Test of 230V@full load
The test result can pass the EN55022 Class B limit with more than 6dB margin.

5.5.2 Conducted EMI Test of 110V@full load
The test result can pass the EN55022 Class B limit with more than 6dB margin.

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