Post History
I have a hunch that the AC which flows through the isolation transformer has quite a bit higher frequency than 1 MHz. The first piece of evidence is this sentence in the datasheet. Each time a ...
#3: Post edited
by
Nick Alexeev
·
2025-11-08T19:22:24Z (10 months ago)
- I have a hunch that the AC which flows through the isolation transformer has quite a bit higher frequency than 1 MHz. The first piece of evidence is this sentence in the datasheet.
- > Each time a PWM pulse is generated, the ac source transmits
- **very high frequency [VHF, emphasis mine, N.A.]** signals across the isolation barrier to allow
- efficient power transfer through the small chip scale transformers.
- [p. 82 in the [ADE7933 datasheet](https://www.analog.com/media/en/technical-documentation/data-sheets/ade7978_7933_7932_7923.pdf#page=82)]
- The second piece of evidence is that Analog Devices has other isolated DC-DC converters with chip scale transformers ([ADuM5242](https://www.analog.com/en/products/ADuM5242.html) among others). They are covered by an EMC application note [AN-0971](https://www.analog.com/en/resources/app-notes/an-0971.html), which mentions up to 300 MHz in the opening sentence. Most of the app note is about the cap between the PCB ground planes.
- > What I am wondering is why go through all this, if a discrete component can achieve the same performance? Are there any advantages of this approach besides saving cents on a discrete Y capacitor?
The PCB plane capacitance has one advantage that it comes with the least series parasitic inductance, compared to SMT capacitors.
- I have a hunch that the AC which flows through the isolation transformer has quite a bit higher frequency than 1 MHz. The first piece of evidence is this sentence in the datasheet.
- > Each time a PWM pulse is generated, the ac source transmits
- **very high frequency [VHF, emphasis mine, N.A.]** signals across the isolation barrier to allow
- efficient power transfer through the small chip scale transformers.
- [p. 82 in the [ADE7933 datasheet](https://www.analog.com/media/en/technical-documentation/data-sheets/ade7978_7933_7932_7923.pdf#page=82)]
- The second piece of evidence is that Analog Devices has other isolated DC-DC converters with chip scale transformers ([ADuM5242](https://www.analog.com/en/products/ADuM5242.html) among others). They are covered by an EMC application note [AN-0971](https://www.analog.com/en/resources/app-notes/an-0971.html), which mentions up to 300 MHz in the opening sentence. Most of the app note is about the cap between the PCB ground planes.
- > What I am wondering is why go through all this, if a discrete component can achieve the same performance? Are there any advantages of this approach besides saving cents on a discrete Y capacitor?
- The PCB plane capacitance has the important advantage that it comes with the least series parasitic inductance, compared to SMT capacitors. The only way to make a low inductance connection is with a broad flat object, and that's what power planes are. PCB vias add series inductance. Many parallel vias reduce the inductance.
#2: Post edited
by
Nick Alexeev
·
2025-11-08T19:08:04Z (10 months ago)
- I have a hunch that the AC which flows through the isolation transformer has quite a bit higher frequency than 1 MHz. The first piece of evidence is this sentence in the datasheet.
- > Each time a PWM pulse is generated, the ac source transmits
- **very high frequency [VHF, emphasis mine, N.A.]** signals across the isolation barrier to allow
- efficient power transfer through the small chip scale transformers.
- [p. 82 in the [ADE7933 datasheet](https://www.analog.com/media/en/technical-documentation/data-sheets/ade7978_7933_7932_7923.pdf#page=82)]
The second piece of evidence is that Analog Devices has other isolated DC-DC converters with chip scale transformers ([ADuM5242](https://www.analog.com/en/products/ADuM5242.html) among others). They are covered by an EMC application note [AN-0971](https://www.analog.com/en/resources/app-notes/an-0971.html), which mentions up to 300 MHz in the opening sentence. Most of the app note is about the cap between the PCB ground planes.
- I have a hunch that the AC which flows through the isolation transformer has quite a bit higher frequency than 1 MHz. The first piece of evidence is this sentence in the datasheet.
- > Each time a PWM pulse is generated, the ac source transmits
- **very high frequency [VHF, emphasis mine, N.A.]** signals across the isolation barrier to allow
- efficient power transfer through the small chip scale transformers.
- [p. 82 in the [ADE7933 datasheet](https://www.analog.com/media/en/technical-documentation/data-sheets/ade7978_7933_7932_7923.pdf#page=82)]
- The second piece of evidence is that Analog Devices has other isolated DC-DC converters with chip scale transformers ([ADuM5242](https://www.analog.com/en/products/ADuM5242.html) among others). They are covered by an EMC application note [AN-0971](https://www.analog.com/en/resources/app-notes/an-0971.html), which mentions up to 300 MHz in the opening sentence. Most of the app note is about the cap between the PCB ground planes.
- > What I am wondering is why go through all this, if a discrete component can achieve the same performance? Are there any advantages of this approach besides saving cents on a discrete Y capacitor?
- The PCB plane capacitance has one advantage that it comes with the least series parasitic inductance, compared to SMT capacitors.
#1: Initial revision
by
Nick Alexeev
·
2025-11-08T18:57:11Z (10 months ago)
I have a hunch that the AC which flows through the isolation transformer has quite a bit higher frequency than 1 MHz. The first piece of evidence is this sentence in the datasheet. > Each time a PWM pulse is generated, the ac source transmits **very high frequency [VHF, emphasis mine, N.A.]** signals across the isolation barrier to allow efficient power transfer through the small chip scale transformers. [p. 82 in the [ADE7933 datasheet](https://www.analog.com/media/en/technical-documentation/data-sheets/ade7978_7933_7932_7923.pdf#page=82)] The second piece of evidence is that Analog Devices has other isolated DC-DC converters with chip scale transformers ([ADuM5242](https://www.analog.com/en/products/ADuM5242.html) among others). They are covered by an EMC application note [AN-0971](https://www.analog.com/en/resources/app-notes/an-0971.html), which mentions up to 300 MHz in the opening sentence. Most of the app note is about the cap between the PCB ground planes.