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Simple 1.2-20V 1.5A Switching Regulator

This tiny regulator board outputs 1.2-20V from a higher voltage DC supply at currents up to 1.5A. It's small, efficient and cheap to build, with many handy features such as a very low drop-out voltage, little heat generation and electronic shut-down.

By Nicholas Vinen

Main Features

• Wide operating voltage range

• Very low drop-out voltage

• High efficiency

• No heatsinking necessary

• Electronic shutdown

• Thermal, overload and short circuit protection

• Soft start

• Provision for power switch & LED

In the December 2011 issue, we presented the MiniReg, an update to our LM317-based 1.3-22V adjustable linear regulator. This has been a very popular kit over the years because it’s cheap, simple and can be adjusted to suit whatever voltage you need.

But while an LM317 regulator circuit might appeal to old dudes and codgers, it’s so “1980s”! For anyone in their thirties or younger, it’s just plain boring. In fact, the LM317 was designed in 1970 by two engineers working for National Semiconductor. That’s over 40 years ago, well before I was born! And while linear regulators are still in use in many applications (yeah, yeah, still boring), these days, just about every computer, monitor and TV (and a lot of other gear) uses switchmode regulation.

Click for larger image
This photo of the MiniReg linear regulator (December 2011) shows just how inefficient it is compared to the MiniSwitcher. This is the size of heatsink it requires in order to handle a current of 1A if there is a large voltage differential between input and output (eg, 14.4V input and 5V output). By contrast, the MiniSwitcher can handle currents up to 1.5A and doesn’t require a heatsink at all, regardless of the input-to-output difference.

The benefit of switchmode regulators is much higher efficiency. This means lower power consumption, less heat and cheaper components (eg, smaller transformers and heatsinks etc). Small size, light weight and low power consumption are particularly important for portable electronic gear.

In short, for a large range of applications, why would you bother with linear regulation? Linear regulators only have to be used if you need very low noise and ripple and for EMI-sensitive applications like radios. For just about everything else, switchmode is the way to go.

Just look at the photo towards the end of this article – it shows how large a heatsink you need to get the rated current of 1.5A from the MiniReg with a 14.4V input and a 5V output (ie, when the power source is a lead-acid battery). That is no longer a small or cheap regulator!

Then there’s the fact that a lot of linear regulators have quite a large “dropout voltage”. This is the minimum difference between input and output voltage. For example, to get a regulated 12V, you generally need at least a 15V input (unless you are using a low-dropout regulator or LDO).

If you are using the MiniReg as a speed controller for the Magnetic Stirrer project in the December 2011 issue, you can’t run the fan at full speed if you are using a 12V power supply. In that application, it isn’t a problem but sometimes the high drop-out voltage is a serious inconvenience (and it increases the dissipation as well, because the supply voltage is higher than it would otherwise need to be).

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