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Significance of primary side sensing to IoT

Posted: 14 Jan 2016     Print Version  Bookmark and Share

Keywords:Internet of Things  IoT 

The signal is transferred from the secondary side circuit to the primary side, providing a feedback loop to modulate the pulse duty-cycle and provide regulation. It is this feedback loop that maintains a constant current or voltage output. These typical opto-isolation devices contribute to high component count and provide less efficiency.

The opto-isolation topology requires numerous components – error amplifiers, phototransistors, and optocouplers – which necessitate a larger footprint. In addition, secondary side regulation results in output current sensing loss, so there is a lack of efficiency in the design. In fact, flyback converter technology is least efficient at the light to medium loads required by these small, integrated electronics.

And in with the new...
PSR is a new primary side sensing technology that reduces the number of components and increases the efficiency of the power supply. This technology is essential to the future of the IoT. PSR reduces part count and achieves a smaller footprint and higher efficiency by eliminating the feedback from the secondary side of the circuit and/or transformer. Instead, PSR regulates output voltage and current by sensing both the current and voltage reflection from the primary-side inductor windings only. Others have attempted primary side regulation, but their technology still needs an additional microchip and a tertiary (third) transformer winding to work, which adds back to the part count. In that type of Primary Side Sensing configuration, information from the auxiliary, or tertiary, winding is sampled. The efficiency of that configuration is also highly dependent on a good coupling between the auxiliary winding and the secondary winding.

As an alternative, the new product removes the need for secondary side sensing, which reduces the amount of circuitry required and does not need a third transformer winding. The TRONIUM PSR works with a forward convertor/controller configuration, which is more efficient than the typical flyback configuration due to the coupling of the topology with the use of TRONIUM capacitive pre-regulation voltage reductions, where the voltage is reduced to near target voltage levels before a transformer is introduced for isolation.

In this instance, the TRONIUM PSR technology senses from the primary side winding and the driver FET directly, using a new complex algorithm equation to account for the full depletion of the secondary winding energy plus secondary part losses. The information is then used to regulate the secondary output voltage by Pulse Width Modulation (PWM). PWM is a method that takes digital information and transports it with an analogue like pulsing signal. The PSR can adjust the PWM based on the output load required, which results in an energy savings.

Since TRONIUM PSR technology does not require optocouplers or error amplifiers, there are fewer components required that have to be powered. The elimination of flyback conversion and opto-isolation circuits reduces the part count by 50 per cent – from about 50 components down to 25. The entire TRONIUM power supply, called Power Supply System on a Chip TM (PSSoC) has an efficiency of 92 per cent at low loads, even during stand-by mode when the system is simply idling.

With "Dial-a-Voltage" technology, this chip can be configured to work with different voltages and can fit into existing power supply topologies. Voltage outputs between 1.7V and 48V can be achieved using the same chip from inputs ranging from 90VAC to 260VAC. This "Dial-a-Voltage" feature maximises the efficiency by setting the output value for each application's requirements and eliminates the need for more than 2,500 different power supply options currently in the market to meet the variation in voltage requirements.

PSR coupled with a forward controller topology is touted play an important role in the burgeoning IoT market, as it's able to provide high power supply efficiency at light and medium loads. The components fit in a smaller package due to the removal of the secondary winding circuitry and the auxiliary winding circuitry. This reduces the cost-to-market for new IoT products. PSR solves the problems of traditional secondary feedback technology while meeting the strict output current regulation required by the portable electronics market.

About the author
Michael Freeman serves as Semitrex's CEO/CTO.


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