DC-DC Converter vs Switching Regulator

Question

As an example, lets say I'm looking to convert 24V to 12V for a circuit that draws 800mA.

I understand that a standard linear regulator is going to dissipate 9.6W so is out of the question here. So if I look on RS Components I find a DC-DC converter THD 12-2412WI and a switching regulator TSR 1-24120.

Am I right in assuming that the 12-2412WI is a DC-DC Buck converter? If so, considering the size, cost and efficiency, why would anybody ever use it as opposed to the switching regulator? Is there some advantage to using one over the other? I've tried looking online but I'm only seeing people compare linear regulators to switching regulators which I don't feel is quite what I'm looking for. Or have I made a mistake in my assumption of how these parts work?

Edit: If I've made the correct assumption and the THD 12-2412WI is a buck converter then will it's circuit not be the same as the TSR 1-24120? If so, why such a difference in parameters/size/cost?

Answer 1

I think you're a bit confused about what these parts do !

The THD 12-2412WI DC-DC converter is an isolated power converter. It is like a mini-mains adapter but with a low voltage input. It takes power from the input and using switching and a transformer makes the power available at the output. But as it is isolated, there is no electrical connection between in and output. This is useful for many applications. One field of application is sensitive measurement equipment where the sensitive input amplifier needs to have it's own isolated power supply. You could achieve the same with a battery but batteries run out which is less practical.

The TSR 1-24120 switching regulator is not isolated. Indeed it is most likely a buck converter. Note how it has only 3 pins, my guess is those are input-ground-output just like on a linear regulator. I'm also guessing that these are a drop-in replacement for a linear 3-pin regulator. As it is a switching converter, it is more efficient than an a linear regulator and it does not need a heatsink. The disadvantage is that this device will be more expensive. On eBay you can get cheap modules based on the LM2596 chip that basically do the same. But check the specs to see if it fits your needs. These more expensive TSR modules might give a "cleaner" output voltage. But it depends on your needs if that is relevant.

So both are switched converters, both are DCDC converters ! Only one is an isolated DCDC converter. Isolation requires more components and also more testing (the manufacturer wants to guarantee good isolation so they probably test it on each device, testing is expensive) making the device more expensive and larger.

Answer 2

The TSR 1-24120 might sometimes be called a "switching regulator" instead of "DC-DC converter" because it is designed to directly replace a TO-220 packaged linear regulator. Both it and the THD 12-2412WI are regulated switching mode DC-DC converters.

Am I right in assuming that the 12-2412WI is a DC-DC Buck converter?

You are not, buck converters are not isolated. The 12-2412WI has an isolated output, able to block a 1.5 kV potential difference between the input and output while transmitting power. It therefore uses an isolated converter topology, most likely a flyback converter

The three-pin linear regulator replacement TSR 1-24120 is most likely a buck converter.

why would anybody ever use it as opposed to a switching regulator?

Because sometimes a portion of a circuit must be galvanically isolated from the rest (for safety or functional purposes). In order to supply power to the isolated section, an isolated DC-DC converter like the 12-2412WI may be used.

Sure, you could design your own isolated DC-DC power supply for a significantly lower cost, but in low volume proucts it would get really expensive to get the converter certified. By using an off-the-shelf product like this, you can just solder the module to the PCB and you are done.

An additional advantage of the 12-2412WI is that some variants can both step the voltage up or down.

Answer 3

Ok, first we need to set our terminology: DC-DC converters (sometimes also called regulators and stabilizers) are divided in two main groups: Linear and switching converters. Linear are working in continuous mode where output is always somehow proportional to the input and lower than the input (example famous 7805). Switching converters come in three groups: step-up (or boost) where output voltage is higher than input, step-down (or buck) where the output voltage is lower than input and boost-buck converters where you can chose output voltage to be either higher or lower than input. Difference and comparison in respect to price, efficiency, etc between those groups you can find anywhere around.

Regarding your components: THD 12-2412WI is very poorly described in the datasheet and manufacturer vaguely specifies it as a DC/DC converter. Only from the application notes I have found a parameter called "fixed switching frequency" that confirms that it indeed is step-down or buck DC/DC converter.

TSR 1-24120 is specified as step-down DC/DC converter, what makes it the same kind of device as THD 12-2412WI. The only differences I see between these two is in input voltage range, efficiency and package type. Usually, switching regulators need couple of external components such as inductors, diodes and capacitors to control their operation, but it seems that in both of these regulator all those components are already integrated in the package.