I have heard about DC DC converters and I understand what they are but what is a DC DC controller? What is the difference between the two? Like this LM5085, I cannot understand the major difference between the converter and controller. Hoping for an explanation.

Thanks in advance!


A switching regulator "controller" implements the logic portion of the overall converter inside the IC but does the heavy current switching using one or more external high current and/or high voltage semiconductor switches.

This allows the power able to be handled to be adjusted to suit the application by using more or less capable switches as required, and often achieves overall performance levels which are not practically achieved within an IC of a given size. The overall result is that the task is partitioned into sections which are best handled by components which are usually able to be price and size optimised compared with using a single IC solution.

The LM5085 that you cite Datasheet here - has a 4.5V to 75V input voltage range. Providing a power IC at this voltage rating is usually expensive.

A typical application circuit (from the data sheet) is shown below. This is rated at about 60 Watts (5A at 12V out, 5B shown on diagram) but by changing Q1 and L1 any sensibly desired power level can be achieved. The ICs cost just under $1 in 1000 quantity at Digikey

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There are basically three options for implementing a DC-DC converter.

  1. A Module Modules have the entire DC-DC converter built into a little cube. These are designed by people that know what they're doing, and optimized for efficiency and EMC. They are good for when a) time to market is critical, and the designer of the end product can't be bothered vetting a power supply and b) when the designers of the end product don't know or want to know anything about power supply design. An example...

  2. An IC When you use an IC, brains, control loop, and the switching transistors are on the same die, usually with the switches in the form of a synchronous rectifier. The end product designer only needs to add caps, inductors, and resistors as needed. The design work is done by the manufacturer, and is implemented by the end product designer. The end product designer will optimize to their particular situation, and is ultimately responsible for the performance and EMC. An example...

  3. A Controller IC This is what you have found. A controller IC has the brains(again, complex) transistor drivers, and control loop on one die. The switching transistors and passive components are all external. Again, the manufacturer of the controller will provide recommendations, but the end product designer is responsible for optimizing and vetting the design.


A DC-DC controller it can be used for buck, boost or flayback converter. The Dc-DC controller consists of a VCC monitor for controlling the state of the device, current power driver for controlling the gate of a discrete P or N channel transistor, fixed frequency oscillator, short circuit protection timer, programmable Soft−Start, precision reference, fast output voltage monitoring comparator, andoutput stage driver logic with latch.

  • \$\begingroup\$ Some controllers can handle a number of topologies as you state. Others may be limited to one or a few depending on the designers aims. \$\endgroup\$ – Russell McMahon Dec 22 '14 at 16:27

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