Battery ChargerLCD-LED DisplayUSB Circuit Diagrams


SIMPLE USB CHARGE: MP4 players, MP3 players, mobile phones, and a variety of devices can conveniently charge through a computer’s USB port. Charging adapters for these devices are typically designed to accommodate the standard USB cable, allowing for charging both from a PC and an adapter. During my examination of a charger utilized in Chinese MP4 players, I came across an exceedingly straightforward charging circuit.

This charging adapter consists of two fundamental components: a simple 5 SMS section that provides the charging output and a charge control section.


The SMPS section of the circuit provides a 5-volt output in the secondary stage. The control section is a straightforward single-transistor circuit employing the S9015 transistor. When a 3.7-volt Li-ion Battery is being charged, a red LED remains steadily illuminated, and upon successful battery connection, a green LED lights up. After a few tests, it became evident that the control section operates consistently across different battery charging scenarios.

The variation in SMPS power and the resistance value of R1 play a significant role in this. For Li-ion batteries with a current range of 180 to 250mA, a resistance value of 5.6Ω is used, while for batteries with a current range of 480 to 680mA, a 1.5Ω resistance value is employed. I observed that the SMPS section of the charging adapter, when combined with the control section, functioned effectively with a 5-volt external connection. This setup proved to be suitable for charging an MP4 player.

If you intend to charge a battery directly, independent of a device like an MP4 player, it’s advisable to include elements D1 and C1 in the second circuit.

China Li-ion Charging Adapter Circuit 

China Li-ion Charging Adapter Circuit

The S9015 is a widely recognized silicon PNP bipolar junction transistor (BJT). Its primary purpose is to amplify low-gain signals. This article aims to provide information on the pin configuration, specifications, circuit applications, equivalents, and other pertinent details pertaining to the S9015 transistor.

Characteristics of S9015 Transistor

  • Type: PNP
  • Collector-Emitter Voltage, max: -45 V
  • Collector-Base Voltage, max: -50 V
  • Emitter-Base Voltage, max: -5 V
  • Collector Current − Continuous, max: -0.1 A
  • Collector Dissipation: 0.4 W
  • DC Current Gain : 60 to 1000
  • Transition Frequency, min: 150 MHz
  • Operating and Storage Junction Temperature Range: -55 to +150 °C
  • Package: TO-92

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