PARTNER FOCUS FEATURE The MinE-CAP IC is designed to


interface with Power Integrations’ InnoSwitch3 and InnoSwitch3-Pro power conversion ICs, and uses a single pin interface to control their operation during start-up and under fault conditions.


Figure 4: Space saving achieved with a MinE-CAP design, compared to a conventional power supply


Figure 3: MinE-CAP circuit for reducing the size of bulk capacitors


become very large. In a charger application, either higher


voltage or higher capacitance are required, but not at the same time. A new technology solution from Power Integrations exploits this condition to enable substantial savings of up to 40% in power supply size without the need to increase switching frequency. The circuit operates by using a switch


to add capacitance when line voltage is low, and to isolate the low voltage bulk capacitors when the input voltage rises above a threshold voltage. The capacitor switch must pass the primary switch current when conducting, so a GaN


device is employed to provide low RDS(on) in a very small area to insure high efficiency. Switching frequency is twice AC line frequency so switching losses are negligible. This permits the designer to employ a combination of low-voltage and high-capacitance devices along with low-capacitance and high-voltage


REDUCING INRUSH CURRENT WITH MINE-CAP IN A FLYBACK POWER SUPPLY In addition to reducing the size of the bulk capacitors, MinE-CAP greatly reduces input capacitance at turn on. This has the effect of virtually eliminating inrush current stress making an inrush current limiter (thermistor or NTC) unnecessary – increasing overall circuit efficiency and eliminating a key hotspot as well as reducing the stress on the bridge rectifier and input filter. The MinE-CAP design is best-suited to


Figure 5: Inrush current i2t characteristic for a power supply design with MinE-CAP and without MinE-CAP but using a conventional 1Ω or 5Ω NTC


capacitors. The space saving for such an approach can be significant – reducing the bulk-capacitor volume by up to 50%. Control circuitry detects when line voltage falls below a


safe threshold (150V) and connects the low voltage capacitor string (typically employing standard 160V rated capacitors) to the line. The controller also ensures that the low-voltage capacitors are kept charged so that they can deliver energy as required, and that the integrity of the capacitors does not deteriorate over time – a problem that can occur with uncharged electrolytic capacitors. In addition, the controller manages capacitor charging during power supply turn on and provides rapid protection during line surges and voltage swells.


non-PFC designs for power supplies delivering between 25 and 75W output power. The circuit also supports non- charger applications that are designed to support power supplies that work in regions with unstable line voltages. The first designs employing the new


technology are already entering production, where the low component count (only five components are required to create a working MinE-CAP circuit) ensures that designs can maximize size reductions while simplifying manufacturing challenges when compared to high switching- frequency solutions.


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MINE-CAP FOR USE IN REGIONS WITH UNSTABLE MAINS VOLTAGES Figure 6: India Version of a switching Power Supply using MinE-CAP compared to a conventional circuit


The MinE-CAP concept removes capacitors from operation when the input voltage exceeds the rated level of the “low-voltage” group of capacitors. In developing economies, the AC line can be subject to random voltage swells that greatly increase the rail voltage for several seconds or minutes. Conventional chargers and power supplies for industrial equipment and appliances typically solve this challenge by fortifying the input stage against such events by using strings of low-voltage


capacitors or employing very large 600 V rated capacitors to achieve a safe operating voltage


for the bulk capacitor stage. A MinE-CAP circuit can be used to isolate the majority of the bulk capacitors during a line surge, leaving a very small high- voltage capacitor (which due to the input voltage can easily store enough energy to prevent 100 Hz ripple on the output) in circuit. This approach means that the input stage for worldwide operation can be reduced in size and cost by the introduction of MinE-CAP switching technology.


/ ELECTRONICS


ELECTRONICS | DECEMBER/JANUARY 2021


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