Building Blocks Simplify and Speed SMPS Design

Jul 1, 2002 12:00 PM
By Sam Davis, Editor, Power Electronics Technology

To aid in design and manufacturability, a newly patented approach allows designers to use standard MOSFETs and transformers with only two windings — giving greater flexibility to meet price and performance objectives. The In-Plug^™ modules from ASIC Advantage Inc. offer this building-block approach to the design and manufacture of robust off-line switchmode supplies, by using internal trimming to eliminate the need for circuit adjustments. These modules provide versatility to build supplies specific to an application with no wasted efficiencies, parts, functions, or space. The building blocks are incorporated in the company's family of standard In-Plug ICs and available for use in building customized dedicated ICs.

You can use the line-side flyback and load-side feedback controllers to address applications ranging from simple low-cost off-line SMPSs to fast chargers requiring hard-to-meet transient response characteristics. Line-side flyback controllers eliminate MOVs and safety-rated capacitors in low-power applications. Load-side feedback controllers allow easy implementation of voltage regulation and current limiting.

The figure shows the present configuration of modules, some of which are currently available and others that are under development.

The IPS10 and IPS15 are highly integrated modules optimized for flyback applications. These controller ICs include a shunt regulator, precision oscillator, biasing, and a PWM with associated comparator and loop compensation components, as well as biasing and protection circuits. They enable stable operation under any load and line voltage. The IPS10 employs an external MOSFET to produce outputs up to 70W. The IPS15 is an enhanced version of the IPS10 featuring soft-start and overvoltage limiting.

Two precision feedback load-side controller ICs for flyback supplies can be used for voltage reference/current limiting or current regulation/voltage limiting. IPS22 is for applications beyond 800mA output, while the lower cost IPS25 is for outputs below 800mA. They produce outputs between 2.6V and 26V and are optimized to operate with the IPS10/15. Features of IPS22 include a precision 2.6V reference, error amplifier with loop compensation, and precision 250mV reference for current limiting/regulation. IPS25 has the same voltage reference and error amplifier configuration, a precision 1.3V reference for current limiting/regulation, and an optocoupler output enhancing noise rejection.

These modules are intended for low-cost, high-efficiency, low-power switchmode supplies with ac input ranging from 90V to 264V and dc from 100V to 350V, employing simple, noncritical, low-cost transformers. They operate with an optocoupler or bias winding feedback, and their adjustable frequency minimizes EMI.

Under development is the IPS201, a dedicated push-pull controller for high-efficiency, low-cost supplies in the range of 40W to 400W — where flybacks aren't normally optimized. It will feature an adjustable oscillator, frequency divider with cross-conduction prevention, PWM, cycle-to-cycle current limiting, and thermal shutdown.

The IPS101 PFC controller, also under development, can be inserted between the supply's rectifier and input capacitor. It charges the capacitor to a voltage slightly above the peak line voltage by drawing a current proportional to and in phase with the voltage. This results in an excellent power factor and quasi-sinusoidal line current waveform. PFC must be followed by a dc-dc converter that isolates it from the line voltage and generates the required output voltage(s).

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