Power Electronics Europe April/May Issue 2022

34 CONVERTER DESIGN www.murata.com Issue 2 2022 Power Electronics Europe www.power-mag.com resonance. At high power, the stress on the LLC switching transistors becomes impractically high and then typically a ‘phase-shift full bridge’ topology is used. This is another resonant circuit in a four-switch bridge arrangement but operates at fixed frequency, with regulation achieved by varying the relative phase of the drive waveforms to each leg of the bridge. This technology is utilized in Intermediate Bus Converters such as the DRQ series [5]. Switched-capacitor converters need no magnetics It is not necessary to use an inductor or transformer in a non-isolated DC/DC converter; switched capacitor arrangements can be used which charge capacitors in series or parallel then set them in parallel or series respectively to step down or up voltages respectively, in discrete multiples. Previously, switch and diode drops have limited the efficiency attainable but with modern MOSFETs and synchronous rectification, 96 %+ can be achieved at 72 W such as Psemi novel switched capacitor technology Figure 5 [3]. There is typically no active regulation and the step up or down is in a fixed ratio, 3 or 4 in [3] but the technique, without an inductor lends itself to modern fabrication methods and low-profile products. Cell-phones require highest efficiency Lower-power non-isolated DC/DC converters find a home in many commonplace electronic items such as cell-phones, where maintaining battery run-time is important and is facilitated by high efficiency of all power conversion stages. Converters that regulate an output with the input higher than, or lower than the output voltage are particularly valuable as a battery loses charge and its output voltage drops. Such converters are often classified as ‘buck-boost’, although strictly this gives a negative output which is not always useful. The SEPIC converter mentioned before (Figure 6), is a popular choice to provide a positive voltage with the input above or below the output. Q1 in the schematic operates as a synchronous rectifier. L1 and L2 can be separate inductors or wound on the same core. Ultra-wide DC input range converters Having a single DC/DC converter that can operate from a multitude of battery voltages, can simplify applications where the manufacturer of the equipment is uncertain which battery source will be used by the customer, for example in railway applications the battery can range from 24 V up to 110 V depending upon the manufacturer of the locomotive and the geographical region. Murata’s IRH250 / IRQ150 satisfy this challenge with a DC voltage input range of 16 V – 160 V DC (Figure 7). Automotive requirements are severe Small DC-DC converters in automotive equipment can be subject to harsh environmental and electrical stress. The automotive AEC-Q qualification test requirements are not generally applicable to power converters so they are often classified as ‘multi-chip modules’ to AEC- Q104. The manufacturer of the device must also have certification to TS 16949 for their quality management system, above and beyond the familiar ISO 9001 standard. The NXJ series in Figure 4 is an example of an AEC-Q104 -qualified part. Literature [1] https://www.murata.com/en- us/products/productdetail?partno=780 3SR-C. [2] https://www.murata.com/en- us/products/productdetail?partno=MY MGA5R04RELA5RA [3] https://www.murata.com/en- eu/news/power/dcdc/2021/0419 [4] https://www.murata.com/en- us/products/productdetail?partno=IRH- 12%2F21-W80PB-C [5] https://www.murata.com/- /media/webrenewal/products/power/d atasheet/drq-11_4-88- l48.ashx?la=en- us&cvid=20200224045920000000 Figure 5: Psemi switched capacitor technology Figure 6: The SEPIC converter operates with input voltage above or below the output Figure 7: IRH250 ultra-wide DC input range converters