LED照明控制器 XC9401设计指南(2/9)

2.Product Features

This series provides simple operation that is suitable for a variety of solution circuits, from non-isolated circuits that use a coil to isolated circuits that use a transformer. The SOT-26 package enables reduction of the board mounting area and easier mounting on the light bulb.

Unlike an isolated type, a non-isolated circuit configuration does not require external components such as a photo-coupler or snubber circuit, making it possible to reduce the number of components, the mounting area, and total cost.

Control Method

Fixed off time is used for the basic control method, and the LED current is monitored by detecting the current in the external power MOSFET to provide a stable power supply for LED lighting. The product series is available in two functional types, the XC9401A type and the XC9401B type, and either can be selected as appropriate for the required characteristics.

Fig.1 XC9401 A type (Non-isolated Circuits Examples)

Fig.2 XC9401 B type (Non-isolated Circuits Examples)

The circuit configuration of the A type is designed to achieve a high power factor by synchronizing the LED current with the input voltage (sine wave).
This circuit configuration makes it unnecessary to add a high-capacitance, high-voltage electrolytic capacitor after the bridge rectifier circuit from the AC input. The input filter removes high-frequency switching noise from the AC line, and thus a low-capacitance ceramic capacitor can be used.
The peak current that flows through the external power MOSFET due to switching constant is made constant in the B type, allowing the LED current to be kept constant.  By keeping the LED current constant, this circuit configuration makes it possible to achieve a stable light source with high efficiency.

Oscillation Frequency

A control method with a fixed off time is used, and thus the switching frequency is determined by the voltage of the connected LED and the input voltage. For details, refer to section 5-1-2.

PWM Dimming

PWM dimming is possible by inputting the PWM signal into the EN/DIM pin.
For details, refer to section 5-4.

Protection Functions

Over-current protection, thermal shutdown, UVLO, and VDD over-voltage protective circuits are incorporated to protect the IC. For details, refer to section 5-5.

Consideration for harmonic wave regulations

With A type and B type of the XC9401 series, each of which has different functions, it is possible to meet harmonic wave regulations. The input current in each type is described below.

In the A type, because the LED current is synchronized with the input voltage (sine wave), the input current waveform is in phase with the input voltage (sine wave) (Fig. 3). For this reason, the input current contains almost no high-order harmonic wave current components and easily satisfies IEC61000-3-2.

In the B type, a high-capacitance input capacitor C2 is connected to smooth the voltage after full wave rectification. The voltage Vrec that has been smoothed after full wave rectification and the input current are shown in Fig. 4. The waveform of the input current varies depending on the capacitance of the input capacitor, and thus input filter can be adjusted to satisfy IEC61000-3-2 Class D (devices with an effective input power of 25 W or less).

Fig.3 XC9401 A type input voltage and input current

Fig.4 XC9401 B type input voltage and input current