Figure 1: The RACM140E series power supplies are available in both closed and open designs. (Image: RECOM)

Basis

Low power PCB-mounted DC/DC converters have not followed the trend towards miniaturisation to the same extent as ICs or surface mount devices, primarily because the magnetic components required in most converters have retained the same manufacturing technology and stayed about the same size for decades. But the miniaturisation of DC/DC converters is significantly influenced by their magnetic cores – due to the material’s intrinsic maximum flux density and the operating frequency, which in turn determines the minimum number of turns. Their size and properties determine the efficiency, heat generation, and ultimately the physical size of the converter.

Modular, low-power PCB-mounted DC/DC converters are produced manually in large quantities in low-cost production facilities. The advantage of this is that a large number of variants can be produced economically in small quantities, even if the manufacture and assembly of the magnetic components is relatively expensive. However, this approach limits the possible complexity of circuits, impedes reproducibility, and restricts electrical performance and miniaturisation possibilities. Materials science and design advances are helping to overcome these limitations.

Solution and examples

primary power supplies, failure of the inverter, and even damage to the power supply and other components. One way to reduce the peak current when a motor is switched on is to connect PTC thermistors, i.e. temperature-dependent resistors, in series with the motor.

Solution and examples

One solution for high starting currents is to use a power supply able to deliver not only the normal operating current of the motor, but also to supply the high short-duration start-up currents. The power supply should also demonstrate a certain overload capacity to withstand the starting currents without shutting down or being damaged. RECOM offers power supplies of this kind in their RACM140E series. These power supplies also offer the advantage of output overvoltage protection, which is set significantly higher than the nominal output voltage to safely handle the counter-EMF voltages generated by the motor.

•    Handling start-up peaks: The series delivers continuous output of 140W and a boost output of 210W for up to 10s.
•    Comprehensive protection against short circuit and overcurrent at the continuous output
•    No problems with counter-EMF voltages: The output overvoltage protection is set considerably higher than the rated output voltage so that it can safely handle back EMF voltages generated by the motor (Fig. 2).

Figure 2: DC motor with PTC for inrush current limitation and optional braking resistor circuit. The AC/DC power supply can handle the motor voltage generated by the counter-EMF thanks to increased output overvoltage protection. (Image: RECOM)Figure 2: DC motor with PTC for inrush current limitation and optional braking resistor circuit. The AC/DC power supply can handle the motor voltage generated by the counter-EMF thanks to increased output overvoltage protection.