Power Module in Isolated DC/DC Bias Power Supplies

Power modules have a wide range of uses and have significant integration compared to discrete implementations. Power modules can offer many options with regard to input voltage, output voltage, output power, number of outputs, isolation ratings, and regulation options.

Below is a simple block diagram of a power module, which includes a transformer driver.

With many options available, you can use a power module in most isolated bias converter applications.
They greatly simplify the design process because you:

  • do not need to specify, design or choose a transformer;
  • only need to include an input and output decoupling capacitor to start the design;
  • can use other options like synchronization, output voltage selection, enable and error signaling, which are available as well.

However, you may sometimes feel a lack of flexibility with modules, specifically in configuring the number of outputs and transformer turns ratios. The selection of modules rated for a 125°C ambient temperature range is less than for the 55°C and 85°C options. Similarly, the number of modules available with fully reinforced insulation ratings is less than those modules available with functional or basic isolation.

Nowadays, some new power modules are much more integrated and compromise on system performance. One good example is UCC12050 from TI. Its switching frequency is much higher compared to general power modules. This allows significant height and weight reduction versus lower switching frequency alternatives. The internal topology control scheme runs closed-loop without an LDO or external feedback components.

UCC12050 brings many benefits to the wide variety of isolated DC/DC bias supply applications. It is designed with an EMI-optimized transformer with only 3.5 pF of primary-to-secondary capacitance and a quiet control scheme. On its own the solution can pass CISPR32 Class B on a two-layer PCB without ferrite beads or LDOs. The device is robust, rated for reinforced isolation of 5 kVrms and 1.2 kVrms working voltage and will operate at 125°C ambient temperature. The family of devices also includes UCC12040, which is rated for basic isolation of 3 kVrms and 800 Vrms working voltage.

UCC12050 is targeted for 5-V input, 3.3-V to 5.4-V output applications requiring 500 mW. Applications requiring higher input or output voltages will need to provide pre-or-post conversion. Also, for designs requiring power above the UCC12050’s derating curve, alternative topologies should be explored.

A comparison between each topology and UCC12050: