Shane Callanan, Director of Applications Engineering at Excelsys Technologies discusses the the future dynamics of modern power supplies
The modern direct-off-line stabilised switch mode power supply is a highly sophisticated, reliable and efficient piece of equipment, on which a whole system will rely for safety, stability and lasting performance.
The latest ICs now require DC voltages as low as 1V, while some circuitry operates at DC voltages up to 100V and beyond. The various DC voltage levels sometimes may require sequencing or the ability to control so that they can be turned on and off in a desired way.
Additionally, for most equipment, galvanic isolation of the DC voltages from the mains is needed to meet international safety standards. There will also be international standards to consider, which will define the interface with the AC mains and surrounding electrical equipment.
In most cases power supplies require some type of feedback loop to regulate output. The power stage has two inputs, power input (Vi) and the duty cycle control. For this to be stable, negative feedback is used.
The output voltage is compared to a reference voltage. The output of the error amplifier is inverted with respect to Vo and is therefore out of phase.
The target here is to keep the difference between the output and reference to an absolute minimum. If the feedback loop has infinite gain for all frequencies, there is perfect regulation regardless of the demands of the load.
Limitations such as sampling, finite gain and bandwidth will reduce the maximum gain and bandwidth of the control loop. This principal will be implemented in some format irrespective of the chosen topology.
Planar Magnetics have provided a major breakthrough in reducing the overall size of a power supply. For many years the transformer has traditionally been a bulky and relatively big component. The possibility of now having the windings on the PCB, and incorporating the core around these windings has had a number of benefits to the overall design.
Recent improvements in PSUs
Successful closing of the loop using Digital Signal Processors (DSPs) has allowed major additional functionality to be implemented. Feedback loops can now be nonlinear and dynamic.
It is possible to have optimum performance over all line, load and transient conditions. You can even introduce a time and/or temperature function that can compensate for thermal drifts of components. In doing so you can also reduce component count, simplify designs, and at the same time increase power density.
Closing the loop digitally is something achievable for quite a number of years now, but the cost of the DSP chips created a barrier until recently. However, we have recently seen a cost reduction to a point where digital control IC’s are price competitive with their analogue counterparts.
The future power supply will be significantly different to the one we see available on the market now. Some new developments have started to make a break through onto the market and will have a direct impact on what we will expect to see from our future power supplies.
Digital Power Management, Digital Control and successful adoption and implementation of resonant topologies are several aspects that will directly impact on what we can expect to see coming down the line. Coupled with more integration of components and circuits into one package, this will hugely enhance the performance capabilities of the Commercial Off The Shelf supply that we know today.
Resonant converters have been around for a long time. However, it is only recently they are seeing increased acceptance. Controllers are becoming more available as there is an absolute need to improve efficiency.
One such topology is the LLC resonant converter. The LLC resonant topology allows for zero voltage switching of the main switches thereby significantly lowering switching losses and boosting efficiency. Efficiencies of 93 percent to 96 percent can be achieved with these converters.
As we move forward, efficiency figures in this range will no longer be market leading but will be the expected performance from your power supply.
All in all we can expect to see an increasingly improved generation of power supplies with additional functionality, higher power densities, and optimum performances over dynamic operating conditions.
Excelsys Technologies
