Power Integrations’ New IC Allows for Smaller Sized AC-DC Converter Capacitors

In recent years, designers have sought to miniaturize the size of AC-DC converters by raising the switching speed. They could then employ filter capacitors with smaller capacitance values and correspondingly smaller physical sizes. Power Integrations claims that through the use of MinE-CAP IC the same or greater overall power supply size reduction can be achieved.  An important benefit of this approach is the avoidance of the need for complex EMI filtering and the increased transformer/clamp dissipation associated with very high-frequency designs.

 

Image courtesy of Power Integrations

 

Comments Power Integrations’ product marketing director, Chris Lee: “The MinE-CAP will be a game-changer for compact chargers and adapters. Electrolytic capacitors are physically large, occupy a significant fraction of the internal volume and often constrain form factor options – particularly minimum thickness – of adapter designs. The MinE-CAP IC allows the designer to use predominantly low voltage rated capacitors for a large portion of the energy storage, which shrinks the volume of those components linearly with voltage. USB PD has driven a major market push towards small 65 W chargers and many companies have concentrated on increasing switching frequency to reduce the size of the flyback transformer. MinE-CAP provides more volume saving than doubling the switching frequency, while actually increasing system efficiency.” 

 

How It Works

The approach is most easily understood by analyzing a typical application. The CHV (high voltage capacitor) must be able to tolerate the full pulsating DC output voltage of the bridge. But notice that it is paralleled with the combination of the CLV (low voltage capacitor) and the MineECAP.

 

Image courtesy of Power Integrations Data Sheet

 

MinE-CAP engages, introducing the CLV into the circuit at low AC line voltage, just when maximum input capacitance is required.  It disengages before the output of the bridge exceeds the CLV’s voltage tolerance. MinE-CAP achieves this by monitoring the voltage across CLV to dynamically engage and disengage this capacitor during every AC line cycle.

Notice the reference in the image above to the InnoSwitch3-CP, a device that can be employed along with the MinE-CAP in many applications.

For an application working with an AC voltage input range of 90 to 350 VAC, the graph below illustrates typical values of the 400 volt CHV and the 160 volt CLV. 

 

Typical filter capacitor ranges. Image courtesy of Power Integrations Data Sheet

 

Reading the graph shows that at 50 watts output, for example, the 400 volt CHV need only be of a typical range 20 µF to as low as perhaps 2 µF, while the 160 volt CLV might range from between 58 µF to 78 µF.

The MinE-CAP IC also serves to dramatically reduce in-rush current, thus rendering both NTC thermistors and large slow-burn fuses unnecessary. 

As summarized by Bhaskar Thiagaragan, Director of Power Integrations India Ltd, “MinE-CAP dramatically reduces the number of high-voltage storage components, and shields lower voltage capacitors from the wild mains voltage swings, substantially enhancing robustness while reducing system maintenance and product returns.”

 

Protection Features

• Input surge protection
• Integrated temperature sensing and hysteretic thermal shutdown
• Undervoltage and overvoltage fault reporting
• Pin open and short-circuit fault reporting

 

Packaging

The MinE-CAP is available in a miniature MinSOP-16A package. 

 

Designing with MinE-CAP and InnoSwitch3

As described, MinE-CAP works well with the company’s InnoSwitch3 IC. Power Integrations has provided two initial design example reports (DERs) pairing the devices:

• DER-626 describes a 65 W USB 3.0 power delivery (PD) power supply with 3.3 to 21-volt programmable power supply (PPS) for mobile phones and laptops.
• DER-822 highlights a 60 W USB 3.0 PD power supply for USB PD/PPS power adapters.