Auxiliary supplies for industrial designs simplified with PI's LinkSwitch

May 20, 2015 // By Graham Prophet
Providing relatively low power rails to power circuitry in industrial designs can present challenges, when the requirement of meeting the latest efficiency standaerds is added. Power Integrations says it can simplify the design of industrial PSUs for 440-VAC line input using its LinkSwitch-4 device.

LinkSwitch-4 uses technology acquired with PI's purchase of Cambridge Semiconductor early in 2015. It now has a reference design for an energy meter PSU that boosts efficiency, and eliminates opto-couplers. The reference design (DER-479) demonstrates an industrial power supply using the LinkSwitch-4 family of CV/CC primary-side regulated (PSR) switcher ICs with a 1200V bipolar junction transistor (BJT). The design supports 440 VAC line inputs and features three outputs which combine to provide up to 11W of highly accurate constant-voltage DC power.

PI comments that Cambridge Semiconductor had developed expertise in driving bipolar junction transistors (BJTs) to maintain them in safe-operating-area conditions, and that experince is embodied in the reference design.

LinkSwitch-4 controllers feature an adaptive base and emitter switched drive scheme to boost switching performance and increase efficiency. The advanced switching technique is beneficial in high-voltage applications as it reduces slow turn-off switching losses and eliminates BJT failures due to secondary breakdown, improving the reverse-bias safe operating area (RBSOA) and system reliability. The LinkSwitch-4 controller’s primary-side regulated sensing methodology eliminates optocouplers, replacing them in the feedback loop with a simple transformer winding. The design uses just 50 mW under no-load conditions while maintaining a fast transient response. The 65 kHz operating frequency minimises transformer size, reducing system cost and PCB footprint.

LinkSwitch-4 devices also compensate for a number of factors including: transformer inductance tolerances; input line voltage variations; cable voltage drop; and external component temperature variations.

Power Integrations adds, “Power supplies for high-voltage systems such as three-phase meters and motor drives can be challenging to develop – efficiency, reliability and component count often suffer in such designs. By pairing the LinkSwitch-4 controller with a 1200 V BJT, the designs become very straightforward and extremely reliable.”

DER-479 is downloadable at

Power Integrations;