Step-Down Switching Power Supply Kits

What is a Switching Regulator?

A switching regulator is a typically a device that controls the flow of electricity in the form of pulses.  By uses pulses, resistance is kept to a minimum and that increases efficiency.  Its like controlling a water valve.  By opening the valve half ways, you get half the total available water flow.  However there is a lot of friction on the half open valve which is what causes you to only get half the available flow.  On the other hand, if you could open the valve for one second and then close it for one second and continue doing this, you would get the same amount of water but in pulses from the valve.  The friction on the valve is much less when its fully open.  Controlling water in this means would put a lot more stress on the downstream side of the valve similar to water hammer. A large reservoir would be required to even out the pulses back into a constant flow of water.  Switching regulated power supplies work quite the same. Switching regulators are therefore more complicated than traditional regulators.  With proper design, the pulsing of electricity can be very advantageous.

This page contains preliminary information. Nothing is set in stone (let alone writing) and may never be. If you are interested in this product, please get in touch with Morris Softronics at msftrncs@midlands.net.

The Step-Down Switcher Kit is intended as a small learning aide for those interested in learning about the simplicities of modern step-down switching regulators. The kit would be available in many flavors and may be ordered not only as a kit but also as a completed product ready for application if desired. The regulator is composed of a state-of-the-art LM2675 and also teaches about transient protection among other safe guards of delicate circuitry.

The switching regulator kit would be available in 3.3, 5, and 12 volt fixed versions, custom fixed voltages and a variable voltage version. The nominal input range of the kit is 6.5 to 40 volts and the output of the custom and variable versions may typically be set as high as 37 volts.

Because the regulator kit is based on the LM2675, it provides an introduction to the latest most efficient yet tiny circuits available to the common individual. Without a heat-sink, the 1.5in x 1.5in through-hole kit will regulate at any differential voltage with a current of 1 amp! It approaches an amazing 95% efficiency.

There are two discretely unique versions of this kit planned:

• 1 ampere (1.2 ampere ICS), 1.5in x 1.5in x 1in
• 5 ampere (6 ampere ICS), 2in x 1.5in x 1.75in (some heat-sinking required)

The 5 ampere version is shown above.  Thumbnail is link to larger image.

The following voltage variations of kits are planned:

• 3.3 volt fixed output, 17 volt max input (optional 40 volt max input)
• 5 volt fixed output, 17 volt max input (optional 40 volt max input)
• 12 volt fixed output, 40 volt max input
• 1.25 to 6 volt adjustable output, 17 volt max input (optional 40 volt max input)
• 3.5 to 15 volt adjustable output, 40 volt max input
• 12 to 36 volt adjustable output, 40 volt max input

There are also some special purpose kits planned:

• 3.6 volt fixed output, 1 ampere, 40 volt maximum input, ideal super-efficient portable CD/tape player power adapter

Customizations are possible, and the documentation for most of the kits will explain some of the customizations that may be possible while you build the kit.

NOTES:

Switching regulators are not as efficient at lower output currents unless they are designed for low current operation. Switching regulators are least efficient at high input voltages and low output voltages. Variable voltage switching regulators do not perform as well as fixed voltage versions. Step-down switching regulators require the input voltage to be slightly greater than the output voltage, approximately 2 volts.

The following charts help depict the benefits of using a switching regulator over a linear regulator. The following data was collected from an LM7805 linear regulator and a prototype Switcher Kit using the LM2675.

Cases 1 and 2 are 5 volts out at 100 milliamperes, or ½ watt output power. Voltage in volts, current in milliamperes, power in watts.

The efficiency of the 1 amp regulator increased to around 85% when a 2.5 watt load was tested at both 12 and 28 volts.

New!  Cases 3 and 4 highlight real world performance of a 5 amp switching regulator.  In these examples, the linear regulator values are calculated from known formulas.  The output was measured at 10.2 watts (5.1 volts at 2 amperes).  Current is in amperes.

New!  Cases 5 and 6 highlight real world performance of a 5 amp switching regulator.  In these examples, the linear regulator values are calculated from known formulas.  The output was measured at 2.5 watts (5.1 volts at 0.49 amperes).  Current is in amperes.

It is apparent from the above tables that a switching regulator can be a lot more efficient than a linear regulator, but there is still a common trend that the efficiency will be less at higher input voltages and lower output powers.

Due to the efficiency of the switching regulator, its an ideal candidate for use in battery powered applications, so the voltage drift of the battery (during charging or discharging) will not effect efficiency. This means longer battery life with smaller batteries. It also means lower drain on other power sources, such as renewable sources.