SLLSFM0A March 2022 – June 2022 SN6507
SN6507 is an open-loop transformer driver without load regulation capability. The output voltage may vary over a wide range load current. Therefore, if a high-accuracy, load independent supply is required, the implementation of a low dropout regulator (LDO) on the output side is strongly advised.
The minimum requirements for a suitable low dropout regulator are:
This means in order to determine VI for worst-case condition, the user must take the maximum values for VDO and VO specified in the LDO data sheet for rated output current (that is, 200 mA) and add them together. Also specify that the output voltage of the push-pull rectifier at the specified load current is equal or higher than VI-min. If it is not, the LDO will lose line-regulation and any variations at the input passes straight through to the output. Hence, below VI-min the output voltage follows the input and the regulator behaves like a simple conductor.
with VIN-max as the maximum converter input voltage and n as the transformer turns ratio. Thus to prevent the LDO from damage the maximum regulator input voltage must be higher than VS-max. Table 9-2 lists the maximum secondary voltages for various turns ratios commonly applied in push-pull converters.
|CONFIGURATION||VIN-max [V]||TURNS-RATIO (N)||VS-max [V]||VI-max [V]|
|24 VIN to 15 VOUT||25||1.38:1||18||25|
|12 VIN to 15 VOUT||12.5||1:1.5||19||25|