1. Identify the regulated quantity
A feedback-method requirement should begin with the quantity being regulated. Constant-voltage and constant-current descriptions concern different output requirements, even when one controller provides both. Calling the circuit a flyback identifies its power-conversion context but leaves this feedback question open. The useful comparison is between the documented paths used to regulate each quantity, not merely between controller category names.
Write the voltage question and the current question separately before considering a replacement. This allows a controller with a mixed arrangement to be described accurately instead of forcing the whole device into one simplified feedback label. A summary that records only primary-side regulation may omit a separately documented optical feedback path for another quantity in the same controller.
Keep the application requirement distinguishable from a manufacturer's available function. The circuit may need a particular feedback arrangement, whereas a candidate description explains what that named device provides. Comparing the two requires the regulated quantity to remain visible. A feature heading detached from voltage or current cannot show whether the candidate addresses the path the design actually needs.
2. Read a primary-side regulation example
TI's UCC28730 description states that the controller provides constant-voltage and constant-current output regulation without an optical coupler. The same introduction identifies information from the primary power switch and an auxiliary flyback winding as inputs to its control. This provides a concrete feedback-architecture example without requiring a reconstructed transformer diagram or assumptions about a different controller.
Read the absence of an optical coupler as part of that named regulation description. It should not become a rule that every isolated flyback omits optical feedback. The distinction matters because isolation describes one aspect of the power supply, while the source of information used for regulation describes another. Retaining both terms prevents a power-conversion category from being mistaken for a complete feedback specification.
For a candidate based on this arrangement, identify the supporting manufacturer description of the regulated quantities and information paths. Keep those statements together rather than reducing the requirement to no optocoupler. The abbreviated phrase leaves out why the controller can regulate in the documented arrangement and gives no basis for deciding whether another primary-side device provides the same required functions.
3. Read the mixed feedback example
The UCC28740 example demonstrates why the quantity-to-path distinction is necessary. TI describes constant-voltage regulation using an optical coupler, while constant-current regulation uses primary-side regulation techniques. Its introduction identifies both optocoupled feedback and an auxiliary flyback winding. Describing this device simply as optical feedback or primary-side feedback would conceal part of the documented arrangement.
A comparison with UCC28730 should therefore show the voltage-feedback difference explicitly while retaining the current-regulation description separately. This is not a claim that the devices are substitutes. It is a way to identify the architecture question that a proposed selection changes. A shared flyback description does not resolve the significance of that change for the existing design.
The optical path also raises a different question from an optocoupler's current transfer ratio. The related CTR guide concerns comparison of that component under its stated conditions. Here the earlier decision is whether the named feedback path uses an optical coupler at all and which quantity it regulates. An acceptable CTR comparison cannot establish the controller's complete feedback architecture.
4. Keep the feedback architecture with its dependencies
Preserve the feedback arrangement at the level where it is documented. A controller description may identify several information sources rather than a single route with one universal name. Associating each source with its stated function makes the architecture understandable without inferring the physical implementation or attempting to select transformer, compensation or external-circuit details from a product introduction.
Keep control behaviour such as forced PWM or pulse skipping outside this feedback classification. Those operating-mode questions may belong in the overall power-supply review, but they do not identify how voltage or current information reaches the regulating function. A selection can agree on a mode label while differing in feedback method, or agree on one regulation path while another still needs review.
A focused sourcing requirement can specify the required voltage-feedback method, current-regulation method and applicable controller reference. If a proposal changes one path, describe that change directly rather than presenting the candidate under the incumbent's broad label. This leaves the engineering assessment precise while making no transformer prescription, compensation recommendation, efficiency comparison or result for the actual power supply.
Sources and further reading
TI's UCC28730 and UCC28740 product-description cores were reread on 15 October 2026 for their stated voltage/current feedback paths. No full-datasheet, transformer, compensation, efficiency or actual application result is claimed.