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The LT3573 is a monolithic switching regulator specifically designed for the isolated flyback topology. No third winding or opto-isolator is required for...
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LT3573 on Analog.com

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LT3573 - 300V Isolated Flyback Converter Diodes

PowerLogical on Mar 17, 2023

Category: Hardware

Product Number: LT3573

Hello All

I am trying to simulated the application on page 23 of the LT3573 datasheet (see picture below)

However, diodes D1 and D2 are not in LTspice's database and I have looked for datasheets and models on the internet so I can make a model, but I can't find any information whatsoever

Does anyone know anywhere else that I can find this information or even suggest an equivalent?

Many thanks in advance

Edit Notes

Moved & tagged
[edited by: emassa at 1:41 PM (GMT -4) on 17 Mar 2023]

PowerLogical on Mar 17, 2023 10:17 AM
0

So after more digging, I have found the models for the D1: CMMR1F-06 and D2:CMMSH1-60. They can be found at the following links:

D1: https://www.centralsemi.com/docs/csm/cmmr1f-06.lib

D2: https://www.centralsemi.com/docs/csm/cmmsh1-60.lib

I mistaken the '1' for an 'i' which was the reason I wasn't finding anything

However, even with the proper diode models I only get 300V out when I have 100uH on the primary and 1.1mH on the secondary for the 1:10 ratio in the application. This seems like an awfully high inductance for the secondary winding. Is this correct?
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Achim on Mar 17, 2023 11:34 AM in reply to PowerLogical
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Hello,

I think the "1:10" ratio stands for the turns ratio N1:N2. Since the inductance depends quadratically on the number of turns, I would even expect a 10 times higher inductance on the secondary side.

best regards

Achim
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ADIApproved

on Mar 17, 2023 3:02 PM in reply to PowerLogical
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Another example,

LT8304 - 100VIN Micropower No-Opto Isolated Flyback Converter with 150V/2A Switch (analog.com)

1000 V Output No-Opto Isolated Flyback Converter (analog.com)
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PowerLogical on Mar 20, 2023 4:14 AM in reply to ADIApproved
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Thank you very much for your responses

I am still quite new to the world of power electronics and your answers have validated my findings and now I know I am on the right track.

Does anyone know if the LT3573 has a sync mode so that the frequency can be synced to an external source like the LT8365?
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Achim on Mar 20, 2023 4:38 AM in reply to PowerLogical
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Hello,

if a switching converter can be synched, the datasheet will typically mention this as a special benefit. (like in the feature list on page 1 of the datasheet of LT8365: "Synchronizable to an External Clock").

Since the datasheet of the LT3573 does not contain the letter sequence "sync", it is not intended to be synchronized.

best regards

Achim
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LT3573 - 300V Isolated Flyback Converter Diodes

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