LT4320 Ideal Diode Bridge Controllers Subverts the Traditional Bridge Rectifier

Ⅰ. What is LT4320?

Ⅱ. How does LT4320 overcome the shortcomings of full-wave rectification?

Ⅲ. Which manufacturer makes the LT4320?

Ⅳ. Pin configuration of LT4320

Ⅴ. Three-phase ideal rectification based on LT4320

Ⅵ. How does LT4320 replace traditional diodes?

Ⅶ. What are the common problems with LT4320?

The LT4320 is an ideal diode bridge controller. It utilizes a low-loss N-channel MOSFET that replaces the four diodes in a full-wave bridge rectifier, significantly reducing power dissipation and increasing the available voltage. As it improves power efficiency, it eliminates bulky heat sinks, further reducing power supply size. By eliminating the two diode drops inherent in the diode bridge, additional margin is provided for low-voltage applications. This MOSFET bridge rectifier design not only achieves high space utilization but also improves power supply efficiency compared to traditional alternatives. The controller can operate for systems from 9V to 72V at input frequencies from DC to 600Hz.

In addition, the ideal diode bridge eliminates thermal design issues and greatly reduces PC board area. The LT4320's internal charge pump supports an all-NMOS design, eliminating the need for larger and more expensive PMOS switching devices. If the power supply is faulty or short-circuited, the product has a fast shutdown function to suppress reverse current transients to a large extent.

Full-wave rectification is simple, but at the same time it has unavoidable disadvantages. Two of the most obvious are thermal dissipation and the bucking of the two diodes, which results in relatively low efficiency. To overcome these challenges, Linear Technology has introduced a new product, the LT4320, which works by replacing the four diodes in a full-wave bridge rectifier with low-loss N-channel MOSFETs. This significantly reduces power dissipation and increases the available voltage (reference circuit diagram). Due to the increased power supply efficiency, the product eliminates the need for a bulky heat sink, which effectively reduces the size of the power supply.

The use of MOSFETs instead of diodes significantly reduces the voltage drop, thereby reducing power dissipation by a factor of ten. The significant reduction in heat dissipation eliminates the need for heat sinks in low power applications and simplifies thermal design in high power applications. In addition, additional margin can be provided by eliminating the voltage drop of the two diodes in the diode bridge, which is very favorable for low-voltage applications. The MOSFET bridge enables rectifier designs with high space utilization and power efficiency compared to conventional alternatives.

The LT4320 switching control circuit smoothly turns on the two appropriate MOSFETs while holding the other two MOSFETs off to block reverse current. An integrated charge pump is responsible for providing gate drive to the external low on-resistance N-channel MOSFETs, and no external jumper capacitors are required. The MOSFETs are selected over a range of power levels from 1 W to several kilowatts, which greatly provides flexibility. In addition, the LT4320 is capable of controlling external N-channel MOSFETs. An integrated charge pump makes it easy to design full N-channel MOSFETs, simplifying the bill of materials and saving money. Compared to P-channel MOSFETs, N-channel MOSFETs are typically smaller in size, more cost-effective, and offer a wider range of options. Since the MOSFET is located external to the controller, it can be easily sized to meet the needs of various applications. In addition, the LT4320 offers a wide operating range, a DC to 600Hz input frequency range, an integrated charge pump with no external jumper capacitors, and a simple design flow. These features make the LT4320 an attractive choice for switching control circuits.

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Pin 1 (IN2): Bridge Rectifier Input. lN2 connects to the external NMOS transistors MTG2 source, MBG1 drain and the power input. lN2 connects to the external NMOS transistors MTG2 source, MBG1 drain and the power input. lN2 pin drives MTG2 gate.

Pin 2 (TG2): Topside Gate Driver Output. TG2 pin drives MTG2 gate.

Pin 3 (BG2): Bottom-Side Gate Driver Output. BG2 pin drives MBG2 gate.

Pin 4 (BG1): Bottom-Side Gate Driver Output. BG1 pin drives MBG1 gate.

Pin 5 (OUTN): OUTN is the rectified negative output voltage, and connects to the sources of MBG1 and MBG2.

Pin 6 (OUTP): OUTP is the rectified positive output voltage that powers the LT4320 and connects to the drains of MTG1 and MTG2.

Pin 7 (TG1): Topside Gate Driver Output. TG1 pin drives MTG1 gate.

Pin 8 (IN1): Bridge Rectifier Input. IN1 connects to the external NMOS transistors MTG1 source, MBG2 drain, and the power input.

This demo board provides efficient three-phase rectification with input voltages ranging from 5 VAC to 28 VAC. Its three-phase ideal diode bridge design eliminates the need for expensive heat sinks (e.g., lines that need to be connected to the neutral) and active cooling solutions that are required for traditional three-phase diode bridges. The cost and size of the overall solution allows for high efficiency 3-phase rectification through the use of SK low-resistance ON devices instead of the 6-diode design used in traditional 3-phase diode designs.

By optimizing the available voltage and reducing power consumption (see thermometer comparison below), an ideal diode bridge simplifies power supply design and reduces supply cost, especially in low voltage applications. An ideal diode bridge also eliminates thermal design issues and significantly reduces printed circuit board area. The LT4320's internal integrated charge pump supports all N-channel MOSFET designs, eliminating the need for larger and more expensive P-channel MOSFET switches. Below is a comparison of the LT4320 with a conventional diode thermal image.

1. Start-up problems: The LT4320 may sometimes fail to start up properly, which may be due to the following reasons: insufficient supply voltage, circuit design problems, or external component failures. Firstly, insufficient supply voltage may cause the chip to fail to work properly. Second, circuit design problems may also cause the chip to fail to boot up properly. For example, some components in the circuit are not connected correctly or the specifications of the components do not meet the requirements. In addition, the failure of external components is also one of the reasons why the chip cannot start normally.

2. Overheating: If the LT4320 heats up severely during operation, it may be due to overload, poor heat dissipation or circuit design problems.

3. Performance degradation: As the usage of time increases, the LT4320's performance may diminish progressively, possibly attributable to the aging of internal components or external environmental factors.

4. Unstable output voltage: This may be due to power supply voltage fluctuations, load variations or circuit design problems.

Frequently Asked Questions

1. What is the primary function of the LT4320?

The LT4320 is a dual ideal diode bridge controller. It allows for the ORing of multiple power sources to provide a more reliable and efficient power supply.

2. What is ideal diode controller?

Ideal diodes are MOSFETs with a control circuit around them (Figure 2), turning on with a low voltage drop (below 50mV) in the forward bias condition (input voltage greater than output voltage) and turning off when reverse biased (input voltage less than output voltage).

3. How does the LT4320 improve power supply reliability?

The LT4320 enables seamless switching between two power sources without the need for external diodes. This helps prevent reverse current flow and minimizes voltage drops, improving overall system reliability.

4. How does the LT4320 contribute to overall system efficiency?

The LT4320 helps improve system efficiency by reducing voltage drops associated with traditional diode ORing methods, thereby maximizing the power delivered to the load.