Variable output voltage control of the InnoSwitch3-CP
Dear Support Team
I am currently working on designing an Flyback SMPS using the InnoSwitch3-CP to provide 19V and 12V outputs. The 12V output will power a Peltier device, specifically the TEC1-12703, which has a rated voltage of 12V, a maximum current of 3A, and a power consumption of 27W. The 19V output will be used to power an IC.
To control the temperature of the Peltier device, I plan to modulate the pulse wave from the MCU to the FB pin, thereby reducing the output voltage through adjusting the switching behavior. (datasheet p16) My goal is to control the output voltage from 12V down to 0V.
ex) 12V -> MCU duty 0% / 0V -> duty 100%
Could you please confirm whether this approach is feasible with the InnoSwitch3-CP? Additionally, I would appreciate any guidance or recommendations you might have for achieving this voltage control.
Thank you in advance for your support.
Comments
Hi, Nanoe
Thanks for your responding.
It is assumed that the output voltage gradually decreases due to an increase in the MCU duty, and thus power supply to the IC is not possible. At this time, assuming that the duty is changed to 0%, does the IC not operate normally again?
If not, I can think of two ways, would that be okay?
1. When the 12V output voltage is varied, 19V is only varied to a level where there is no problem with IC power supply. It then lowers 12V to a certain level of voltage and outputs 0V through the comparator.
2. Step down the voltage through a buck converter just behind the rectifier and supplies power to the IC. And apply the MCU to the FB pin to change the output voltage.
In the second case, can't it be controlled to 0V?
If not, should I output 0V through the comparator like the 1st method?
What other ways are there?
Thank you for your support
Hi,
We do not recommend this implementation. If you want to control single output, we strongly recommend using separate transformer and IC. With regards to the comparator, I have not done this, you can try but I do not think this is feasible.
Regards,
PI-Nanoe
Hi,
Thank you for reaching out our forum.
We reviewed your requirements, and it is not possible to implement this. Based on the information provided, your design is dual output. This means every change at the 12V output will also change the output voltage of 19V. With this, you will need to have two transformer and two IC if you want to control 12V voltage without affecting the 19V.
For the variable output voltage, this will depend mainly on the voltage divider resistor or voltage across fb pin that was used in the system. Just like in any chargers, there are multiple output voltages that is already known. With this, we already know what feedback resistor needed to connect from fb pin to the microcontroller. For your reference, please see DER-536. This design can output 5, 9, and 15V.
With regard to the duty cycle from 0V-12V with respect to fb we have not tried this. This implementation may trigger the protection features/AR of the InnoSwitch if voltage goes to 0V. Unfortunately, we do not have any documents or data that may support this.
Regards,
PI-Nanoe