flyback converter Integrated flyback converter design for maximum 45W power
Whether it is inverters, AC servos or household appliances and consumer products, the power semiconductors in the BM2P06xMF-Z series manage without coolers and additional passive components. Everything you need is integrated.
Auxiliary power supplies are an essential part of industrial inverters to supply various DC voltage levels to gate drivers and controllers. The right choice of AC / DC devices reduces design time and system complexity. This saves development and production costs. ROHM’s new BM2P06xMF-Z ICs feature integrated 730V Si MOSFETs and target single-phase 85 ~ 264V AC systems. The simplified auxiliary power supplies and SMPS design benefit designers; conventional solutions based on discrete components, on the other hand, increase the risk of failure and the complexity of the circuit.
Limitations of conventional AC / DC ICs
In recent years, AC / DC converters for industrial and consumer applications have required not only to support AC voltage from 85 to 264V to meet the world’s various AC power grids, but also to comply with international standards such as “Energy Star” for energy saving and safety standard IEC 62368. It is also crucial that AC / DC converter ICs are surface mountable to reduce factory assembly costs, but as DMOSFETs with high loss and flat MOSFETs are still widely used in AC / DC converter ICs. Until now, it has been difficult to deliver high power in a surface-mounted package. Traditional discrete MOSFET-based solutions also require additional passive components and heat sinks, which are not only expensive and time consuming, but also take up more space.
Advantages of the AC / DC ICs with the designation BM2P06xMF-Z
To solve these problems, ROHM has developed high output power surface mounted AC / DC ICs called BM2P06xMF-Z. The package of these flyback ICs is shown in Figure 1. They are very compact at 12.8 mm x 10.3 mm x 2.65 mm and housed in a SOP20A SMD package. In this package, the BM2P06xMF-Z devices integrate a low-loss Super Junction MOSFET with an optimized PWM control circuit to enable easy development of 85 to 264V AC / DC converters. The use of a surface mount package supports automated PCB assembly to reduce factory assembly costs. The functions implemented in the BM2P06xMF-Z ICs ensure compliance with the security standard IEC62368.
Thanks to the integrated solution in one house, the BM2P06xMF-Z ICs do not require any passive components or cooling plates. The reduction of passive elements and cooling plate saves space, development time and system costs, and then the ICs also reduce the risk of device failure and increase the overall system reliability. Finally, the elimination of the discharge resistance and the low standby power control technology of these ICs ensure an unusually low standby power consumption, which increases the performance and efficiency of the power system.
design and product selection
Supply voltages up to 60 V (VCC) is supported, eliminating the need for an external power supply circuit and reducing costs.
A simplified circuit of an AC / DC step-down converter is shown in Figure 3, the supply voltage (Vac, in) is 230 VAC. This means: the intermediate circuit voltage (Vdc, in) is 325 V, while the reference voltage (Vref) of the transformer is assumed to be 250 V – given a transformer rotation ratio of 10: 1. The switch-off voltage (Vsurge) for MOSFET is 100 V. To select the correct MOSFET for the power supply circuit, the breakdown voltage of MOSFET must be higher than the sum of Vdc, in, Vrefl and Vsurge.
Figure 3 also explains how to determine the breakdown voltage of MOSFET. The sum of the voltages (Vdc, in + Vrefl + Vsurge) is 675 V. Therefore, a MOSFET with a nominal voltage of> 675 V is required for this auxiliary power supply circuit. The MOSFET voltage marking or breakdown voltage for the BM2P06xFMF-Z ICs is 730V, which is higher than the sum of these three voltages. So the BM2P06xFMF-Z ICs have sufficient breakdown voltage to support the single-phase AC input voltage.
The BM2P06xFMF-Z devices integrate a 730V silicon MOSFET and a PWM controller enabling a switching frequency of 25 to 65 kHz. The ICs can operate at a maximum transition temperature of 150 ° C. They support a supply voltage of 11 to 60 V. All ICs have an overload protection, an X-Cap discharge function and a brown-out function. Table 1 shows three variants with different on-resistance values. Table 2 describes the achievable output power for the BM2P06xFMF-Z family. Depending on the on-resistor of the MOSFET, outputs between 10 and 45 W are possible.
45W SMD package reduces installation costs
Combined with 730V SJ MOSFET is also start-up and optimized control circuits in the SOP20A package. In addition to being compatible with input voltages from 85 to 264 VAC, the surface mount package supports high output power up to 45 W (24 V × 1,875 A = 45 W), which has been difficult to achieve in the past. Figure 4 shows the comparison of the output power of standard packages with perforated pins and the maximum achievable output power of the newly introduced SOP20A package. The latter significantly reduces assembly costs as they allow automated assembly, which is not possible with ordinary through-going housings.
90 percent less consumption in standby mode
The BM2P06xFMF-Z ICs reduce standby power consumption by at least 90 percent compared to standard products. To do this, the semiconductors use a control circuit (X-capacitor discharge function) that uses ROHM’s high voltage process and analog technologies to meet the safety requirements of the IEC 62368 standard even without a discharge resistor (Figure 5). By omitting the discharge resistance and due to the optimized control of the switching frequency, the ICs consume only 17 mW in standby (0 W output power, 230 VAC).
Standard is also a noise reduction mode that attenuates noise from the isolation transformer components. This mode can be turned off to reduce the standby power. It is activated when there is concern about noise from insulated transformer components or to minimize the amount of work required for countermeasures.
Increases reliability with fewer components
The new semiconductors help reduce the number of power supply components, reduce the risk of power semiconductor failures, and increase overall reliability. Figure 6 compares the required components between the standard product and the new BM2P06xFMF-Z product. Operation is permitted over a wide VCC-Voltage range from 11 to 60 V. The maximum permissible supply voltage is 60 V, twice the standard products – and thus provides higher reliability against external interference and overvoltages.
The optional external step-down circuit components are typically a zener diode, resistor, capacitor and a transistor. The integrated super-junction MOSFET is designed with overvoltage robustness to increase avalanche tolerance by more than 30x compared to standard DMOSFETs or standard plane MOSFETs.
The evaluation board and the heat distribution
ROHM provides an evaluation board with the designation BM2P060MF-EVK-001. It contains BM2P060FMF-Z 0.70Ω IC (Figure 7). The test results of the evaluation board are shown in Figure 8. The maximum output power is almost constant (> 45 W) and depends less on the input voltage. The thermal image of BM2P060MF-Z during operation confirms that the transition temperature is below the limit. Cross temperature Tj is <90 ° C at T-one= 25 ° C. If the ambient or house temperature (Tc) would rise to 85 ° C, then the transition temperature of the chip would be Tj= 150 ° C, and thus below the specification.
Summary of key facts: The BM2P06xMF-Z power ICs require no heatsink, no additional passive components, and no additional controls. This reduces design time and system complexity and saves development and production costs. The power modules are suitable for auxiliary power supplies and for SMPS units with 85 to 264 V AC supply voltage. to support them in the development phase. To support the design work in the development phase, there is the evaluation board BM2P060MF-EVK-001. This makes it possible to evaluate the performance of the IC.