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Posted on 01 June 2019

Small Footprint also Occupies Less Board Space

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New power package together with high frequency switching meets efficiency and EMI specs while driving down solution cost

By Andrew Smith, Power Integrations Inc

 

Switching power supplies are now manufactured around the world in huge numbers to be used in wall adapters and internal power supplies for all kinds of equipment. Design engineers have worked long and hard to squeeze out the last cent of cost, gain every percent of efficiency and fit their designs in the smallest possible space. To achieve significantly more requires a breakthrough technology. Power Integrations Inc. (PI) has developed a new power package, named eSIP, which is much smaller than the venerable TO-220 package it has been developed to replace. Moreover, eSIP is specifically designed for high noise power supply environments. As an example, when PI’s latest TOPSwitch-HX integrated off-line switcher IC is used in the new eSIP package, a 132kHz flyback converter power supply can be constructed that delivers major cost and performance advantages.

New eSIP package

The eSIP package stands proud of the circuit board just like the traditional TO-220 and exhibits the same low thermal impedance, yet measures less than 10mm above the PCB - half the height of the 45 year old TO- 220 package. The small footprint also occupies less board space. This much smaller package meets the increasing market demand for slimmer electronic products such as LCD monitors, flat screen TVs and set-top boxes.

eSIP provides TO-220 performance in a smaller package

The eSIP has a pin layout that allows it to self-index, providing the correct component height when inserted into the PCB without the need for a spacer. A simple push clip provides a low cost method for attaching the devices to the heatsink. The clip securely holds the eSIP/heatsink combination in place, easily meeting the requirements of the standard IEC 60068 shock and vibration test suite.

The heatsink attached to the eSIP package is at Source potential, therefore electrically quiet. As such it does not require an insulating pad.

TOPSwitch-HX TOPSwitch-HX is an off-line switcher combining a 700V power MOSFET, multi-mode controller, integrated current limit, undervoltage and overvoltage fault protection features, over temperature protection and other control circuitry onto a monolithic device (See Figure 2).

TOPSwitch-HX typical flyback application

The TOPSwitch-HX family covers a power range from 6.5W up to 333W . The IC requires few external components (See Figure 3), and when designed to operate at 132kHz, excellent system cost savings can be realised. The TOPSwitch-HX power supply uses a multi-mode control scheme that allows it to transition seamlessly between different switching modes, always delivering optimum efficiency under any load condition. This multi-mode feature allows TOPSwitch- HX designs to meet all existing and proposed energy standards including Energy Star 2.0 and EU COC requirements.

Schematic of 40W low cost LCD monitor power supply using TOPSwitch at 132kHz

Frequency jitter and optimised switching techniques are applied to minimise both radiated and conducted EMI. This together with PI’s unique portfolio of low cost EMI shielding options for the power transformer reduces the size and number of EMI filter components. The MOSFET is constructed using a lateral technology which exhibits very low parasitic capacitance. This allows it to switch at 132kHz without incurring high switching losses. Another important characteristic of the technology is the high breakdown voltage – 700V. This enables a higher turns ratio to be used in the transformer, which in turn results in a lower secondary voltage for a given DC output, leading to power dissipation and cost savings in the output rectifier diodes.

Cost saving

A raft of cost savings accrue from the combination of the TOPSwitch-HX, eSIP package and 132kHz operation. The choke (L1 in Figure 3) and transformer (T1) can be smaller than for 65kHz designs, with a consequent transformer cost saving of more than 30%. The high frequency, highly continuous designs possible with PI also reduce output ripple – reducing both size and number of output capacitors required, further decreasing the cost of the output stage. The tight production tolerances of the TOPSwitch-HX and built in line over-voltage protection coupled with the 700V breakdown voltage of the switching MOSFET means that line surge protection circuitry (typically a MOV) can be eliminated without reducing circuit reliability.

The eSIP package and TOPSwitch-HX represent a breakthrough technology in terms of ability of the power supply manufacturer to cost reduce production while fully meeting increasingly tough EMI requirements and environmental efficiency standards.

 

 

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