I am trying to understand in what type of situation I will need an isolated DC-DC converter instead of a non-isolated one. What are the design criteria that can lead one to one way or another?
In my case, I am looking at a Boost Converter design.
Electronic – Advantages of Isolated DC-DC Converter over non-isolated
componentsdcdc/dc converterdesign
Related Solutions
An SMPS controller1 IC may support multiple converter topologies. But a single IC almost never supports all common converter types.
There is a family of converters derived from boost converter: flyback, SEPIC, boost proper. A controller that can do boost, usually can do the rest of the boost family too. Usually, one controller can't do both buck family and boost family.
1 SMPS controller IC drives external power switches. SMPS converter IC has power switches on board. Converter ICs tend to be less versatile than controllers.
While it may not apply to the specific device from XP Power, application note slyt211 from Texas Instruments explains how small (<5W) isolated power converters such as the DCP010512 operate. Essentially, inside the converter, there is a set of switches and an isolation power transformer. The controller generates a waveform that allows for power to be rectified on the isolated side. An unregulated device has an internal diagram such as:
However, the ISL2412 you wish to use has regulated outputs. This adds additional complexity to the device. The LTM8048 datasheet shows how such a regulator could be implemented, along with the other switching electronics:
For dual-supply operation, Murata's BEI15 Series includes a block diagram for regulated outputs:
Further, Digikey reveals that this BEI15 Series module is not encapsulated, allowing you to see how components are arranged:
Here, you can see the control IC on the load side in the front-left of the module, the board-level transformer in the middle of the board with a snap-in ferrite core with the Murata logo, and two switching devices along with ceramic capacitors on the far edge of the device.
Finally, the Murata BWR Series devices includes a nearly complete diagram of a higher power (ca. 30W) isolated converter using synchronous rectification on the load side:
Additional references:
- The DFC10 Series from Power One has a block diagram on page 48
- This image of a SHHN000A3 Series converter from GE on Digikey
- The DSP1 Series from Power One has a block diagram on page 2
- This image of a PTB48510 converter from TI on Digikey
- The IMX70, IMY70 Series from BEL has two block diagrams on page 3
Best Answer
If you have high currents or frequencies riding around one part of a circuit that you'd like to protect another part of the circuit from, isolation is certainly an option. For example, if you have a microcontroller driving a high-current motor with PWM, you can optoisolate the PWM pin on the microcontroller, then power up the motor circuit with an isolated DC to DC. Doesn't work if you don't optoisolate (or isolate in some other way), obviously.
If you're building a medical device with patient leads, isolation of the patient leads might be critical to meeting safety standards. An isolated DC to DC, along with isolation of all the analog and digital signals that need to connect to the patient would be in order.
Note that an isolated DC to DC becomes a nonisolated DC to DC if you connect the grounds!! Also, if you're putting test points into your board, be sure to include one for every ground, and don't forget that its not hard to connect isolated grounds with your oscilloscope ground clips accidentally!