4.2W GU10 LED Lighting Driver with Primary Side Feedback

Abstract This article will introduce you to a low-power LED lighting driver solution using TI's offline primary-side sensing controller TPS92310. Thanks to the constant on-time flyback topology and primary side sensing, the solution enables high efficiency and good line and load regulation. For the GU10 replacement LED bulb, the reference design PMP4325 has a suitable small form factor (30mm & TImes; 18mm & TImes; 10mm), which supports common AC line input and 3 or 4 LED series output with a constant output current of 350mA. Experiments show that in terms of LED lighting, the solution has good line and load regulation, high efficiency and overall LED lighting protection.

1 Theoretical operation

1.1 TPS92310 Controller

For low-rated LED lighting, the single-stage flyback structure is an attractive topology. The reason why single-stage flyback structures can be widely used in LED lighting is as follows:

l Galvanic isolation reduces overall bill of materials (BOM)
l High power factor using a special control architecture (eg constant on-time control, etc.)
l Smaller size than other two-level topologies
Although single-stage flyback structures have many advantages for LED lighting, there are still some issues that need to be addressed. These issues include:

l High power factor
l Stable line pressure and load regulation for primary side feedback (PSR)
l LED open or short circuit protection
The TI TPS92310 controller is a single-stage, primary-side sensing AC/DC controller that drives a constant current for high-brightness LEDs. It operates in zero current detection conversion mode (TM). During the half cycle of the line pressure, the "on time" (TON) is almost constant. Therefore, it has Power Factor Correction (PFC) itself because the peak current of the main winding changes as the input line pressure curve changes. The TON is adjusted to adjust the LED current to a preset level set by an external sense resistor. TON is also used in the control design of flyback, boost, and step-down converters. This converter operates in conversion mode and uses a constant on-time control to achieve high power factor. In addition, TON can be used to control buck converters that operate in conversion mode, and their general purpose LED drivers use peak current control.

Primary side inspection does not require the use of optocouplers and secondary side circuitry, resulting in fewer components and a more compact PCB solution. In addition, the controller features cycle-by-cycle current limit, output short-circuit protection, output overvoltage protection (OVP) or open LED protection, short-circuit LED protection, and thermal shutdown protection, all of which provide protection for LED lighting. Measures.

1.2 Constant on-time control

In conventional boost power factor correction converters, a constant on-time controlled switching mode is typically used to keep the input current in phase with the input voltage for high power factor and low total harmonic distortion (THD).

For a single-stage flyback topology operating in conversion mode, it is not inherently power factor corrected because the duty cycle and frequency are constantly changing during the shape cycle. Therefore, under these conditions, power factor and total harmonic distortion are not ideal. Fortunately, the single-stage flyback topology operating in filter mode uses a fixed (constant) TON, still achieving high power factor and low total harmonic distortion. As shown in Figure 1, the average input current is an approximately sinusoidal wave with the same phase as the input voltage.

Figure 1 Current waveform during TON and TOFF
In this design, the TPS92310 controller is configured in constant on-time control mode. If a large-capacity capacitor is connected to the COMP pin to filter the 100-Hz line ripple ripple for a single-stage flyback application, the switch The opening time can be fixed. However, in order to reduce the size of the board, the reference design is not a single-stage structure without power factor correction, so we used a small-capacity compensation capacitor to maintain the stability of the control loop. Since the DC input voltage of the flyback structure is relatively stable, the turn-on time is almost constant.