Novel low-power integrated AC-DC converter solution - Power Circuit - Circuit Diagram

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With the continuous evolution of semiconductor technology, it has provided an advanced platform for system designers and circuit designers to innovate technologically. This has resulted in many novel and fashionable portable electronic products being introduced to the world, such as PDAs, 3G mobile phones, various personal health care devices, and endless gaming consoles. Most of these portable electronic products require high-end switching power supplies for powering or charging. Additionally, there are numerous advanced portable instruments, industrial control devices, and even everyday items like electric razors that rely on switching power supplies. Against this backdrop, PHILIPS launched the STARplug power IC product line.

This series not only meets the demands of micro-power consumption, high reliability, and miniaturization required by portable electronics but also satisfies safety and environmental protection standards.

About the STARplug Product Line:

STARplug consists of two series: the TEA152X series and the TEA162X series (as shown in Table 1). The TEA152X series was introduced back in September 2000. The TEA162X series is an enhancement of the TEA152X series, finalized in May 2004. Both series share similar block diagrams, circuit structures, external lead arrangements, and most electrical parameters. The key difference lies in the internal high-voltage start-up current source of the chip: the TEA152X series has an Icharge of 1.5mA (typical), whereas the TEA162X series features an Icharge of 500µA (typical).

STARplug employs a multi-chip architecture. All control sections are integrated on one chip using a BiCMOS process, while the power section is fabricated on another chip using the EZ-HV process and then optimized on the same substrate. From a manufacturing standpoint, Philips utilizes an advanced full-oxide isolation process (or media isolation process), which offers several advantages:

1. Eliminates the latch-up effect, a unique failure mode in CMOS circuits;

2. Facilitates the integration of analog, digital, and power circuits on the same chip;

3. Reduces chip size compared to standard PN junction isolation;

4. Minimizes leakage current, making it suitable for high-temperature environments;

5. Reduces parasitic capacitance, minimizing cross-talk and EMI through the substrate;

6. Enhances resistance to external sparks and reverse polarity.

All of these factors contribute to supporting the high performance and reliability of STARplug.

From a circuit design perspective, an important feature is the concept of valley switching. Typically, the power dissipated by the power MOSFET is the primary source of power consumption in a switching power supply. It plays a critical role in the reliability, stability, and efficiency of the power supply. The power consumption of a power MOSFET generally comprises three parts:

1. Power consumption when the MOS transistor is off, i.e., when VDS is high. This power consumption is primarily determined by the leakage current between the drain D and the source S, which is related to the chip manufacturing process. IDS(off) typically ranges in micro-amps, making this portion of power consumption negligible.

2. Power consumption when the MOS transistor is on, i.e., when VDS is low. This power consumption is mainly determined by the on-resistance RDS(on) between the drain and the source. This depends on the geometric parameters of the chip design.

3. Dynamic power consumption of the MOS transistor, i.e., the power consumption during switching between cut-off and conduction. This can be calculated by the formula below:

Philips' circuit designers analyzed the formula and realized that reducing the dynamic power consumption of the switching power supply could only be achieved by lowering VDS during switching and the frequency f when the load decreases. Typically, VDS is around 380V. By circuit resonance, VDS can be reduced to nearly 0V, decreasing the dynamic power consumption of the MOS transistor by several orders of magnitude. For this reason, a valley detection circuit was added to the circuit design. Once the circuit resonates, the correct "valley" is detected, and when VDS enters the "valley," a rising edge pulse is applied to the gate G and source S for PWM control.

In the PWM chips of the 1990s, the operating frequency f was mostly fixed. To reduce power consumption, particularly standby power, STARplug adopts a flexible circuit design with an adjustable frequency. The frequency set by the user is the operating frequency at full load. As the load decreases, the operating frequency also decreases accordingly. This ensures that standby power consumption remains under 100mW.

In addition, the STARplug series of chips starts with a high-voltage current source. Once the IC enters normal operation, the high-voltage current source is automatically shut off, thereby reducing circuit power consumption. This demonstrates the entire circuit design philosophy of reducing power consumption. The effective reduction of power consumption in both the power MOSFET and the control section enables the integration of the power device and control circuit into a single package, significantly reducing peripheral components. Furthermore, to ensure reliable circuit operation, comprehensive protection functions are provided, including cycle-by-cycle overcurrent protection, undervoltage lockout, overvoltage protection, overtemperature protection, winding short-circuit protection, and demagnetization protection.

STARplug Function Description:

1. Structure of STARplug: Figure 1 is a block diagram of the internal circuit of STARplug. It’s clear that the diagram includes two parts: the power MOSFET and the control circuit. The power MOSFET is mainly used for power transmission and conversion. The control circuit has three major tasks:

1. Achieving rapid response to all protection functions;

2. Accurately detecting valley levels;

3. Controlling the duty cycle (i.e., PWM function).