Ask Direct to Engineers
Industrial-grade step-down DC/DC converters providing long-term supply guarantee and available in small-reel sales
The Leading-Edge Synchronous Rectifying Converter Holds the Key to Power Savings and Downsizing for Industrial Equipmet
Industrial Grade Step-Down DC/DC Converter Series
－ Part 2 －
– I’ve heard that the long-term supply guarantee for LB products and the capability to answer the need for small-reel sales contribute to power savings in and downsizing for industrial equipmet. If that is the case, tell us about DC/DC converters for LB products in concrete terms.
As I mentioned in the beginning, at present we are offering a product lineup consisting of 16 models of synchronous rectifying step-down converter ICs with integrated MOSFETs and 2 models of controller type converter ICs. It goes without saying that in terms of basic specifications, such as operating temperature ranges, these products are industrial-grade products. I’ve brought with me tables that illustrate this point, for you to see.
– The DC power supply for industrial devices conjures up the image of a supply unit that takes 12V or 24V, which is a typical bus voltage in industrial devices, for input, and supplies 5V and 3.3V, which are system voltages, to the board.
The maximum input voltage ranges for the integrated MOSFETs type in the table include 7V and 20V products in addition to the 40V product that appears to fit the industrial bus voltages. What roles do they play?
The 40V product fits in the applications you mentioned, as it can handle the 24V bus as well as the 12V bus. Because there are not many integrated MOSFETs synchronous rectifying products that are capable of accommodating 24V, this may be good news for the designers. The 20V product can basically accommodate 12V input, and even 5V in some cases. The 7V product is based on the assumption that the input voltage is stepped down from 5V/3.3V, which was stepped down from 12V/24V. Because of the increasing popularity of devices, such as MCUs and FPGAs that run on a 3.3V voltage or less, the 7V products play a role of secondary DC/DC converters that step down the low voltage stepped down from bus voltage levels. LB products are required not only in high voltage rating products, but also in low-voltage devices.
To make this point clear, I brought another table, which shows model-by-model input voltage handling capabilities with respect to standard 3.3V, 5V, 12V, and 24V input voltages, and output currents that are produced.
– For stepping down applications in industrial equipment, especially from 12V and 24V, my impression is that the diode rectifying type DC/DC converters are in general use. What is intended by the series, which is a synchronous, rather than diode, rectifying type?
It is a fact that the diode rectifying (nonsynchronous rectifying) type is widely used in the bus voltage stepping down applications for industrial equipment. In particular, these components must contend with relatively high voltages, such as 12V and 24V. From the standpoint that is a bus power line, given that power is distributed from the main source, the occurrence of external disturbance must also be taken into account. For this reason, robust power supply units are required. It is in this sense, I think, that conventionally the diode rectifying type has enjoyed considerable popularity, supported by past track records in sales.
By contrast, the synchronous rectifying type, starting with the inroads made into battery-powered devices, including laptop PCs, has now become a standard power supply unit for mobile devices, for which high efficiency is essential. As a matter of fact, whereas generally the diode rectifying type has a maximum efficiency above 80%, the synchronous rectifying type can achieve high efficiency surpassing 90%. First of all, the greatest advantage of the synchronous rectifying type lies in high efficiency.
In recent years, small size, as well as power savings, has become a mandatory requirement. The field of industrial equipment is no exception. The rule of the game is such that bulkiness and some sacrifice in efficiency cannot be tolerated for the sake of robustness. To perform on this kind of playing field, I believe that for power supply we must aggressively tap into the synchronous rectifying type that can offer high efficiencies.
– It seems that the synchronous rectifying type is being used in various electronic devices, but what accounts for the fact that it is not employed that extensively in industrial devices?
It’s a hard question (smiles wryly). It seems that in many cases prospective customers think twice in terms of track records before adopting the synchronous rectifying type for industrial applications. Actually, for years there have been synchronous rectifying type products that offered a high degree of voltage rating, providing actual performance that is deemed acceptable by normal standards. Because the synchronous rectifying type is used more extensively in consumer products, the popular perception may be that they are not well-suited to industrial applications.
Including these items, the LB product is designed to answer requirements specific to industrial devices, in both performance and other product-specific aspects as well as long-term supply guarantee, small-reel sales, and other sales strategy aspects. We would like to dispel any concerns associated with product images.
– I now understand that the use of the synchronous rectifying type improves the efficiency of power supply and contributes to power savings.
What about downsizing? I’ve heard that when compared with the diode rectifying type generally the synchronous rectifying type requires a complex design with an increased number of components.
Although that would be a fair assessment, I think the complexity issue is applicable to those products using a controller-type IC. The series includes two controller types. Other members of the series contain integrated MOSFETs. The required external components consist of one inductor, input/output capacitors, setting/adjustment resistors, and a few capacitors. When this is compared with the commonly available diode rectifying type, because it requires an external Schottky diode, the diode rectifying type ends up requiring an increased number of main components. Newer synchronous rectifying types are fabricated with the integration of as many components are possible. The same is true of the controller type as well. So, the only difference is whether transistors are internally or externally provided. In terms of the number of required components or the amount of labor required in designing a power supply, because the synchronous rectifying type requires one less diode, I think it would be safe to say that the synchronous rectifying type holds an advantage over the diode rectifying type.
Let me now touch upon another important factor on size. Given the same number of components, what affects the size of the final product is the sizes of the components themselves. All ICs themselves may be small, but in the power supply circuit what stands up in terms of size are the inductor and the input/output capacitors. When the switching frequency is high, simply small inductance and capacitance can be used, and accordingly the size can be reduced. Generally, in terms of minimizing power losses and ensuring control, it is easier to increase the switching frequency with the synchronous rectifying type; synchronous rectifying type devices capable of MHz switching operations are not rare. In reality, in terms of footprint in most cases the size of external components, rather than the size of the IC or the number of components employed, is the overriding factor. As an example, photographs are provided for you to see, comparing the BD9E300EFJ with integrated MOSFETs and 40V input and a diode rectifying type of the same capability. It is evident that the former takes up approximately only one-half the footprint of the latter, with a considerably smaller inductor, and not requiring the use of a diode.
– In that sense, am I correct to assume that the LB product offers material advantages in efficiency and size that contribute to power savings and downsizing, in addition to the offering of long-term supply guarantee and small-reel sales that provide security and convenience for customers in the field of industrial equipment?
That is exactly what the series is intended to accomplish. I would like to invite you to evaluate it not only when designing new products, but also from the standpoint of adopting it for a modification of existing products.
※Small-reel sales are available on a case by case basis. If interested, please contact us on an individual basis.
Industrial Grade Step-Down DC/DC Converter Series – Part 1 -
- Ask Direct to Engineers
- Routine Requirements in Industrial Applications: Long-Term Supply Guarantee and Small-Lot Sales
- ROHM’s step-down DC/DC converters comprise a series of products intended to meet the needs in the industrial markets. The series is designed not only to withstand rigorous operating conditions...