# Isolated Power Supplies for Inverter Gate Drivers

I am using a 3-Phase IPM IGBT Inverter Module in motor driver. This module has built-in gate drivers which require 4 Isolated power supplies for their operation. In all I have to design 5 Isolated Power Supplies as shown in the attached drawing.

My input is 2-Phases (380V AC) and the output will be x5 regulators 7815. All 5 outputs will have isolated GND from each other. Max current from each output is less than 500 mA.

If cost is the main factor then how can this be achieved? Should I wound 1 big 50 Hz step-down transformer (380 VAC to 24 VAC) with 5 separate secondary windings or is there any better design technique than this?

The IGBT module is following:

• Are bootstrap power units not an option? May 1, 2019 at 12:32
• I have no idea what are bootstrap power units and how do they compare with isolated power supplies. May 1, 2019 at 12:41
• Bootstrap drivers: Have a look at these answers . May 1, 2019 at 13:05
• This answer looks useful. || This also. | May 1, 2019 at 13:09
• Even if you aren't yet aware of it, you probably have a maximum limit on the mutual capacitance between the "isolated" power supplies. (They may be isolated at DC, but they are never perfectly isolated at AC). This may prohibit or restrict certain topologies involving shared cores. Jun 20, 2019 at 3:28

Should I wound 1 big 50 Hz step-down transformer (380 VAC to 24 VAC) with 5 separate secondary windings...?

No. There are at least two alternatives that will likely be less expensive.

One possibility would be to convert 380 V, 50 Hz to a higher frequency and use that for the primary of a single transformer.

Another possibility would be to use 5 individually isolated, 380:?? V SMPS's.

In order to make a valid decision, you need to estimate the costs based on your anticipated manufacturing location, volume etc.

• I am looking at the combination of your both of the above alternates. "5 individually isolated SMPS's" looks like a good idea along with "high frequency at primary". How about if I use 5 small common-mode filter coils as isolation transformers and drive them at high frequency at the primary. On the secondary I do rectification and then 7815. Do you think it will be practical? May 1, 2019 at 11:36
• I would not expect common mode filter coils to have the correct number of turns for the voltage.
– user80875
May 1, 2019 at 12:15

Can you supply the thing with power for the lower Vcc of the low side drivers? That would make this a low voltage problem with an isolation requirement which is easier to deal with.

Royer oscilator driving a pot core with 5 secondaries, 5 * {diode, cap, 7815}, job done? Shunt regulated flyback? Lots of ways to skin this.

Alternatively, and it might be cheaper, just buy 5 isolated DC/DC modules and run them off the supply for your control circuitry, 15V, 7.5W DC/DC is not expensive in terms of a system with the sort of 380V IGBTs that need 500mA up em.

• Are DC/DC modules inputs outputs are isolated? Any good module? May 1, 2019 at 12:45

Look into a multiwinding flyback converter. That is likely to be least cost option. You should further consider isolation voltage requirements, isolation capacitance requirement, and required power ratings also.

Your Bridge rectified 3 phase DC bus volts will be around 500 VDC .This is too much for an isolated flyback SMPS using orthodox parts .Some countries use 480 VAC meaning even higher DC bus voltages .A two transister Flyback will be reliable if 1200V switching devices are used .Efficiency wont be brilliant but it will cope with wide mains variations .