Using a Switching Regulator! Design Your Own DCDC Converter

Published by DevicePlus Editorial Team at March 13, 2021

Make a DCDC converter with a switching regulator

A switching regulator IC is a power supply IC that obtains the desired voltage value from a certain DC voltage and is used to control switching DCDC converters.
There is also a circuit that uses a Zener diode or a three-terminal regulator to create the desired voltage (step-down) from a high voltage. However, if a large current of several A is required, the step-down is performed with a switching regulator.

Switching regulator ICs are easier to use than expected

Switching regulator IC ROHM BD9E301 is pictured here. The SOP8 package is for surface mounting, but it can also be used for universal boards via a conversion board.

Advantages of a switching regulator

The advantage of using a switching regulator in power supply circuits is “efficiency”.
Some external components are required if you’re going to use switching regulators. Unlike a three-terminal regulator, it requires more than just an IC and a capacitor, which may give the impression that it’s a little difficult to attach.
If you know the operating principles of the switching method, you may think “You have to attach various oscillators and coils, right?” However, most functions of recent switching ICs are built into the IC, so there are few external parts, while circuit design takes less time and effort.
There are various methods for step-down circuits that lower the voltage, but the method that uses a switching regulator can achieve a high conversion efficiency of 80-95%. Other methods include the use of a three-terminal regulator, but here, efficiency is often 50% or less, resulting in wasteful power consumption and enormous heat generation.
When connecting a large load to the step-down circuit, it’s possible to create an energy-saving circuit that generates less heat by using a switching regulator.

Reference link: Switching regulator | Electronics tips
https://www.rohm.co.jp/electronics-basics/dc-dc-converters/dcdc_what5

Let’s make a DCDC converter circuit

Let’s make a DCDC converter using a switching regulator IC.

We’ll use a DCDC converter that can output 5V / 2A from the input of a 12V power supply. With this output specification, you can also move USB devices, so you can give your own device USB charging functionality.
ROHM’s BD9E301 is used for the switching regulator IC. Since this IC has a built-in FET, it supports an output of up to 2.5A and is equipped with a function that allows the output voltage to be freely adjusted with a wide input voltage range (7-36V) and an external resistor.

Data sheet for BD9E301. A circuit design example is described in the data sheet of the switching regulator, so make a circuit with reference to this.
Source: 7.0V-36V input, 2.5A MOSFET built-in 1ch synchronous rectification step-down DC / DC converter –BD9E301EFJ-LB (E2) | ROHM Co., Ltd.

In addition to the basic specifications, the switching regulator data sheet also contains circuit design and pattern layout examples, so we will create the circuit while referring to the data sheet.

Switching regulator IC placed on the conversion board and mounted on a universal board.

Since BD9E301 is a surface mount IC, a conversion board is used for the universal board. If you use a conversion board, the amount of heat dissipation may be insufficient, causing malfunctions, so be careful about the amount of current and heat generation when using conversion boards.

While looking at the application circuit on the data sheet, solder the electronic components to the board. Since the output voltage is determined by the ratio of the voltage dividing resistors of R1 and R2, set R1 to 12kΩ and R2 to 3kΩ, and use the same parts as the data sheet for the other elements.
Since the switching power supply is a circuit that repeats ON / OFF at high frequencies, the components should be mounted as close to the IC as possible so that the wiring distance does not become too long. In a sense, placement is where you need to focus most with a switching regulator.
Since an explanation of the basic layout is included, we will make the circuit while referring to the arrangement of parts.

The back of the completed DCDC converter. DIP parts are mounted on the surface, and the surface mount coils are mounted on the solder surface. There are few parts to be mounted, and a DCDC converter using a switching regulator can be made with a resistor, several capacitors, and one coil.

When 12V is applied to the completed circuit, 5V is output. Since the output voltage is maintained by the feedback, 5V is always output even if the external voltage fluctuates. This switching regulator IC can output up to a power supply voltage x 0.7V, so it will theoretically operate even if the voltage drops to 7.2V.

Now that we have created a 5V / 2A power supply circuit, let’s attach a USB terminal to the output section so that power can be supplied to USB devices.

If you attach a USB terminal to your own 5V DCDC converter, you can also charge USB devices. This photo shows an iPad charging. The heat generation was unexpectedly small, and the battery could be charged stably.

As you can see, you can easily make a 5V output power supply circuit even with a switching IC. It may be interesting to add a USB charging function for increased functionality when making a circuit.

When actually commercializing a switching power supply, there are various issues, including compliance with PCB layout and EMI (electromagnetic interference) regulations, but the circuit design itself can be easily made using a switching regulator IC.

Proper use of a 3-terminal regulator and switching IC

As introduced so far, recent switching ICs have few external parts and plenty of materials for circuit design, so it is easy to mount switching step-down circuits.

In the actual power supply circuit design, you may be wondering whether to use a switching regulator or a three-terminal regulator.

Switching regulators are attractive due to their high levels of efficiency, but depending on the application of the circuit, their advantages may not be fully utilized. For example, when the current is high despite only using a microcomputer and a few LEDs.
Even if the efficiency is improved in a circuit of several mA, the practical merits can be lost.
In addition, the efficiency of switching power supplies decreases as the load current decreases (conversely, the efficiency of 3-terminal regulators is higher), while the drawbacks – such as the large number of parts and noise ripple – can become more conspicuous. In such cases, using 3-terminal regulators has greater merits when it comes to total cost.
In general, do not decide that “Switching regulators are better because they are more efficient!” Instead, it’s important to select an appropriate method in consideration of power consumption and circuit size.

The differences between a switching regulator and a linear regulator. Both regulators have advantages and disadvantages, and the method to be adopted must be selected for the right situations. Three-terminal regulators are classified as linear regulators.
Source: Advantages and Disadvantages, Comparison with Linear Regulators | Tech Web
https://techweb.rohm.co.jp/knowledge/dcdc/s-dcdc/02-s-dcdc/88

Summary
When you hear the word “switching regulator”, you may initially think that it’s “difficult to make”, but it doesn’t take as much design effort as you might think to actually use it. Plus, you can create a highly efficient power supply circuit with only a little effort.
If the switching regulator can be used easily, you can freely control the voltage of the circuit – for example, using step-up, inverting, and buck-boost, in addition to step-down – and the range of the circuit design will be expanded.
The really difficult part of designing a switching power supply is the pattern layout that determines how to arrange the parts and the EMI countermeasures that comply with the regulations of each country. Since it’s possible to make it as soon as you try it, using a switching regulator is a good option even in electronic work.
We used a surface mount type switching regulator IC, but there are also DIP-shaped ICs that can be used for universal boards and switching regulators with built-in coils, so switching ICs are easy to use even in electronic work. In addition, the latest products include a type that can output a current of 7 to 8A with the built-in FET.

If you’re making a power supply circuit with a 3-terminal regulator and a large radiator, or you’re making a gadget by connecting a DCDC converter module, why not try a circuit design with a switching regulator IC?