In the development of electronic equipment, the efficiency of power supply is important. Not only in Japan, but also in power companies around the world, the promotion and improvement of power factor correction machines is becoming increasingly important. Here we introduce AC/DC power supply technology that combines power factor correction with standby high efficiency.
First, a brief description of the power factor and power factor correction (PFC) is given. The so-called power factor refers to the ratio of the effective current to the total current. The power factor sets the phase difference between the voltage and current of the alternating current to φ, and calculates the power factor = COSφ, and the sine wave with no phase difference between the voltage and the current is 1. Simply put, a simple resistive load does not produce a phase delay due to voltage and current waveforms, with a power factor of one.
However, most modern electronic devices use a switching power supply that uses capacitors to smooth the AC voltage (referred to as capacitive input rectification smoothing). When the smoothing capacitive load is used, the input AC voltage flows only in a state higher than the smoothing capacitor voltage, the conduction angle becomes small, and the current waveform becomes a non-sinusoidal current including a high-frequency component.
Even if the same power is consumed, the power supply terminal has to flow a large amount of current (for example, when the power factor is 0.5, the peak current flows twice as much as the power factor 1), the power company must be directed to the high frequency component. Non-sinusoidal currents, countermeasures to deal with excess power generation and damage to equipment, resulting in increased costs.
High-frequency current specifications have been implemented in countries around the world for specific power and above, and are implemented in national laws. One way to comply with this specification is to use a power factor correction circuit (PFC) to bring the input current waveform closer to a sine wave to suppress high frequency current.
The power factor correction method is mainly divided into a passive type using an inductor and an active type using a power element switching. Although the passive circuit composition is simple, it cannot be used in response to a wide range of input voltages, and it is difficult to miniaturize. The active type can be easily miniaturized in response to a wide range of input voltages. However, active power factor correction circuits (PFCs) are less efficient due to their own power consumption. Especially in the standby state, it is particularly remarkable.
Power factor correction circuit and high efficiency are the best of both worlds
ROHM has developed an AC/DC converter IC (BM1C001F) that combines a power factor correction circuit with high efficiency and built-in PFC control. This product is equipped with a new function that can turn ON/OFF the PFC controller with any power and PFC output. control method. Through these technologies, the Enegy Star 6.0 standard of international specifications is also adopted while greatly reducing the standby power. In addition, by integrating a power factor correction circuit (PFC) controller and a quasi-resonant circuit (QR) controller, it is possible to reduce the amount of external components by 20%, which contributes to downsizing of the power supply.
The new product has many features: First, it is equipped with the PFC controller ON/OFF setting function to improve the conversion efficiency at light load and reduce the power consumption during standby. Monitor the load power on the secondary side, turn the PFC controller ON/OFF according to the power level, especially in the load range (75W or less) that does not require PFC control, which can improve the power conversion efficiency.
When the power supply of 100W class is used, the standby power can be less than 85mW at AC100V and below 190mW at 230V AC at AC100V, which meets the requirements of Energy Star6.0 (developed by US Environmental Protection Agency) below 210mW.
With ROHM's original PFC output control method, AC power can achieve high efficiency conversion in all countries of the world. The global AC power input is different. The conventional PFC IC design output voltage is a fixed value. When the boost ratio is large, for example, when the PF output is set to 400V during AC100V input, the switching loss becomes large, resulting in low efficiency.
This product suppresses the inefficiency of the power factor correction circuit (PFC) by outputting a new PFC output control method by outputting a PFC output voltage that matches the AC input voltage. For example, the efficiency of a 100W class power supply at AC100V input is estimated to improve conversion efficiency by approximately 2% compared to a fixed PFC output.
Second, a quasi-resonant circuit with high efficiency and low noise characteristics is used. This mode can reduce EMI interference through the soft switching mechanism; the external switch MOSFET and current sense resistor improve the freedom of power supply design. In addition, the built-in BURST function, light load and high efficiency. Thirdly, by integrating the power factor correction circuit (PFC) controller and the quasi-resonant circuit (QR), the number of external parts required is greatly reduced, and the number of external parts is successfully reduced by about 20%.
Excellent power product development and enrichment support system
When composing a power supply circuit, simply using an excellent IC does not mean that a good power supply can be constructed. In order to construct the best power supply circuit, in addition to the selection of ICs, many design techniques such as the selection of passive parts such as capacitors, coils and transformer winding designs, and PCB working negatives are also necessary. Therefore, as with selected ICs, it is also important to screen vendors that can support this application design.
ROHM not only develops and sells ICs, but also provides a professional team that supports the design of customers. Provides the best power solution with consumer specifications (output voltage, output current, etc.), including AC/DC converters, DC/DC converters, and discrete components such as MOSFETs, diodes, resistors, and complete circuit design. Support services.
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