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The Dreaded "File Test" on an LT4320 Ideal Diode Bridge Controller

Ryan Huff - PoE Applications Engineer
Kaung Htoo - PoE Applications Engineer
Jul 9th 2013

The LT®4320/LT4320-1 are ideal diode bridge controllers that drive four N-channel MOSFETs, supporting voltage rectification from DC to 600Hz.  See how they can be used to replace conventional diodes:

 

Figure 1. LT4320 Replacing Conventional Diodes Schematic

 

By maximizing available voltage and reducing power dissipation (see thermograph comparison below), the ideal diode bridge simplifies power supply design and reduces power supply cost, especially in low voltage applications.  An ideal diode bridge also eliminates thermal design problems, costly heat sinks, and greatly reduces PC board area. The LT4320’s internal charge pump supports an all N-channel MOSFET design, which eliminates larger and more costly P-channel MOSFET switches.

Thermograph of Passive Diode BridgeFigure 2. LT4320 vs. Conventional Diodes Thermograph

 

The LT4320 has very robust MOSFET control scheme.  If the power source fails, chatters on and off, or is shorted, the controller quickly turns-off the MOSFETS minimizing reverse current transients.

 

The LT4320's robustness is demonstrated via the dreaded "file test".  Since the file (also known as a rasp) has many teeth, lightly scraping the AC power source's output terminal over the file applies power intermittently in rapid succession to the ideal diode circuit.  See the following schematic representation of the test setup:

 

The Dreaded "File Test" on an LT4320 Ideal Diode Bridge Controller Figure 3. File Test Setup

 

and, here is the circuit in action!

 

 

Here is a guide to the scope waveforms in the video:

 

The Dreaded "File Test" on an LT4320 Ideal Diode Bridge Controller Figure 2. LT4320 File Test Waveforms

 

As can be seen in the yellow output voltage waveform, throughout the test, the LT4320 ideal diode not only survives but, it continues to full-wave rectify the input.
 
The LT4320 is designed for DC to 60Hz voltage rectification, while the LT4320-1 is designed for DC to 600Hz voltage rectification. Higher frequencies of operation are possible depending on MOSFET size and operating load current.