Minimizing Electrolytic Capacitor Size with Tiny ICs - EE Times India

Power Integrations announced its latest MinE-CAP solution, which is used in high power density AC-DC converters with universal input. MinE-CAP technology reduces the size of high-voltage electrolytic capacitors (bulk capacitors), and also reduces the overall size of the adapter by 40%. MinE-CAP devices also greatly reduce the inrush current, eliminating the need for NTC thermistors, thereby increasing...

Power Integrations announced the latest product

Suitable for high power density AC-DC converters with universal input. MinE-CAP technology reduces the size of high-voltage electrolytic capacitors (bulk capacitors), and also reduces the overall size of the adapter by 40%. MinE-CAP devices also greatly reduce the surge current, eliminating the need for NTC thermistors, thereby improving system efficiency and reducing heat dissipation.

Electrolytic capacitors take up a lot of space in AC/DC power supplies and usually limit the overall size of the battery charger. Power Integrations' goal is to use low-voltage capacitors to store most of the energy, thereby reducing the size of these components.

Traditional power conversion solutions reduce the size of the power supply by increasing the switching frequency to allow the use of smaller transformers. MinE-CAP not only aims to reduce the size, but also avoids the EMI and dissipation challenges associated with high-frequency design. Applications include smart phone chargers, home appliances,

, Lighting and cars.

The market is always looking for efficiency. Consumers demand fast charging, but at the same time, they want small chargers that can withstand higher power density. The output range requires new and complex algorithms to adapt to market demands through dynamic fine voltage and current adjustments.

The implementation of GaN technology makes it possible to reduce heat sinks by taking full advantage of its better switching and on-resistance characteristics. "In addition to GaN, another factor to consider when discussing power efficiency is the switching frequency," said Andrew Smith, Director of Training at Power Integrations. He added: "When you want to reduce the size of the power supply, the traditional method is to increase the switching frequency. Therefore, we will see many applications on the market to increase the switching frequency."

He also added: "PowiGaN switches can improve efficiency-no heat sink or heat sink is required. At the same time, InnoSwitch3 devices introduce a thermal foldback function, without corner restrictions and peak power, and can be quickly charged.

By increasing the switching frequency (> 300 kHz), the size of the transformer can be reduced, but this process will bring heat dissipation, EMI and efficiency issues to the actual flyback implementation, so it is necessary to add other components to mitigate these effects. "This also means that it is mechanically difficult to build a power supply because you now have more components," Smith said.

The increase in switching frequency has brought the need for additional circuits to reduce buffer and switching losses, thus losing some of the size advantages previously obtained. Smith said: "Another component on the primary side (Figure 1) that needs to be considered is the electrolytic input bulk capacitor."

He also said: "This is an important part of controlling peak power and will become an ideal choice for further reducing the size of the power supply. What we see is a technology to reduce the size of the input capacitor." Smith said.

He added: "The input voltage and the energy required for the output determine how much capacitance is needed. So, in terms of size, it all depends on the input voltage range you are using and the amount of output power you want to provide.

The energy stored in the capacitor is proportional to the applied voltage and the square of the capacitance. Smith said: "For high-voltage lines (176-264 VAC), we need less capacitance, for low-voltage lines (90-132 VAC), we need to increase the capacitance by 4 times." Smith said.

The bulk capacitor must be large enough to withstand the high voltage in the wide input power range (ie, 264 VAC), which means about a 400 volt capacitor. "The problem with this is that the 400 volt bulk capacitor is much larger than the 160 volt bulk capacitor. We have done a side-by-side comparison, where the size of the 10 uF 400 volt capacitor is roughly the same as the size of the 100 uF 160 volt capacitor. The power requirement for 65 watts is usually 100 uF. So this is the problem. This is why the bulk capacitor is so large that it must support high voltage and provide high capacitance.” Smith said.

The wide input range requires high voltage and high capacitance capacitors, which makes the device large. What Power Integrations does is to introduce integrated solutions by reducing the size to a minimum.

MinE-CAP is an intelligent controller that determines whether the input voltage is low enough to add extra (low voltage) capacitance to the circuit. The advantage of this is that we have a small high-voltage capacitor and a larger low-voltage capacitor. In this way, you can greatly reduce the space occupied by the large capacity capacitors.

"Another advantage of this is that we have now removed most of the capacitance originally seen in the circuit and reduced the inrush current, which is related to the size of the large-capacity capacitor. Therefore, the inrush current of the power supply should be low Many. This means that we can avoid installing surge limiters and other protection circuits on the power input stage. Therefore, we can actually improve efficiency." Smith said.

The surge current is proportional to the size of the bulk capacitor and therefore proportional to the input voltage. Larger surge current will cause the input rectifier to withstand greater pressure, so it needs good robustness to withstand the surge current. Usually, the designer inserts a surge current limiter, thermistor or equivalent device on the input stage to limit the surge current. By using MinE-CAP, the surge can be reduced by more than 90%, so there is no need to add a surge current filter, which can improve efficiency.

The inrush current may be> 100 A in a short time, which will cause a strong thermal shock to the rectifier. The thermistor is designed to provide high impedance for its channel, but using MinE-CAP can reduce this impact.

MinE-CP technology works best between 25 watts and 75 watts, which is very suitable for market areas that require fast charging. "Depending on the application, we can actually reduce the size of the entire power supply by as much as 40%."

The MinE-CAP package can provide a good thermal connection while minimizing heat, thus protecting the device. MinE-CAP benefits from small size and low R

(Turn on) PowiGaN™ GaN transistors to actively and automatically connect and disconnect various parts of the bulk capacitor network according to the AC line voltage conditions. MinE-CAP greatly reduces the number of high-voltage storage components and protects low-voltage capacitors from mains voltage fluctuations, thereby greatly improving durability, while reducing system maintenance and product returns.

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