I am an electrical engineering student working on the power supply component of my senior design. I am running into an issue with my flyback converter.
I am currently using an TI's LM5022 chip with the PMP7760 reference design also provided by TI. All information on this can be found at http://www.ti.com/tool/pmp7760. I am not altering their design at all, using all the same components as provided by their BOM. My input is the wall voltage sent through a transformer and rectified to create 75V.
TI's design states that the output can be up to 1.5A 21V. However, whenever i attach a load to the output the voltage sags significantly to reduce the current output. For example, i have attached a 60 ohm load to the power supply to draw 1/3 amp and the voltage output reduces from 21V to 5V. I have verified that my rectifier stage does not sag through measurements and by swapping out my rectifier with a lab DC voltage supply, so the issue is definitely within the flyback converter.
This is my first usage of a flyback converter, so please forgive my ignorance. I am using the transformer suggested by TI in their reference design, so i would hope that the transformer would not be saturating. The only other thing i can see that may be an issue is the fact that their is no feedback from the main output back to the switching chip. The feedback comes from another winding of the transformer that is not loaded. So i do not understand how the chip is supposed to react to a change in the load without any feedback.
Does anyone have experience with this type of voltage sag or have any suggestions on how to attack this problem? I am running out of ideas and would greatly appreciate any help provided.
I am currently using an TI's LM5022 chip with the PMP7760 reference design also provided by TI. All information on this can be found at http://www.ti.com/tool/pmp7760. I am not altering their design at all, using all the same components as provided by their BOM. My input is the wall voltage sent through a transformer and rectified to create 75V.
TI's design states that the output can be up to 1.5A 21V. However, whenever i attach a load to the output the voltage sags significantly to reduce the current output. For example, i have attached a 60 ohm load to the power supply to draw 1/3 amp and the voltage output reduces from 21V to 5V. I have verified that my rectifier stage does not sag through measurements and by swapping out my rectifier with a lab DC voltage supply, so the issue is definitely within the flyback converter.
This is my first usage of a flyback converter, so please forgive my ignorance. I am using the transformer suggested by TI in their reference design, so i would hope that the transformer would not be saturating. The only other thing i can see that may be an issue is the fact that their is no feedback from the main output back to the switching chip. The feedback comes from another winding of the transformer that is not loaded. So i do not understand how the chip is supposed to react to a change in the load without any feedback.
Does anyone have experience with this type of voltage sag or have any suggestions on how to attack this problem? I am running out of ideas and would greatly appreciate any help provided.