LYT6079C device cooling
Hi,
We want to use LYT6079C in one of our projects. It is a 50W isolated power supply with output voltage and current control (current control command from user).
In PI Expert online we tried to design our converter. There is an issue with temperature of the device. For our application, the device losses are 0.9W
We will you this device in an enclosed environment. The ambient might be at 80-85 deg (nearly). PI Expert online results are as follows,
1. If we want to use 2 oz (70u), 2 sided copper pcb, it is showing the area must be of 2153355 sq mm (3337 sq.inch) which is not possible.
2. If we select Aluminium extruded heatsink type, it is giving sink part number as 581002B02100G, with TO-220 package type
How we can mount heatsink on this device as this is InSOP-24D package, is there is any cooling mechanism other than copper clad on PCB for this device?
I am attaching link for PI Expert design file for reference.
Regards,
Sai kiran
Comments
Hi,
Thanks for your reply.
1. Help me in understanding how to lower the switching frequency of the IC. Whether it is done by transformer design means changing the primary inductance value. If it is yes, then how switching frequency gets automatically adjusted based on transformer primary inductance.
4. We need to have our design in lower PCB size. So, what if we increase copper thickness from 2 oz to 4 oz by maintaining same area of 1 sq in, will it reduce the temperature. And also what if we remove solder mask of the copper clad connected to source pin.
5. Why the source pin temperature must maintained below 110 deg C, what if we increase up to 125 deg C, as minimum thermal shutdown is at 135 deg C (Provided we will go with higher PCB Tg rating upto 150 deg C). And what is the temp gradient between source pin and junction.
Hi Kiran
1. If you lower the TRF inductance, The energy charge and discharge on the transformer is slower. The secondary side of the IC request the primary to switch every time it received enough energy base from the Is pin voltage threshold. Since energy charge and discharge rate is slower on the TRF, the Secondary side of the IC request the primary to switch at slower pace lowering the switching frequency. I would suggest you use the PI Expert design tool to better understand what parameters are affected with changing FSW.
2. Yes, The larger the volume of the source copper pad, the lower temperature.
3. 110 C is Ideal so as not to trigger the thermal foldback at (124C Junction Temp). Junction Temp is higher at 110C and it could trigger thermal foldback. But you can try to increase the case temp a little but provided its ok for you to foldback at worst case ambient temp condition
Hi,
Thanks for your reply.
I have one more question. In our requirement, we need to turn ON/OFF power supply from a micro controller i.e., digital output (High-ON-3.3V, Low-OFF-0V). Can we achieve that using InnoSwitch or Lytswitch. Please suggest us the way to do it.
Hi Sai Kiran,
Thanks for using PI LED driver products. LYT6079C should be able to handle your input and output requirement at extreme ambient temperature with proper transformer design and IC heatsinking. At 85C ambient requirement the IC case temperature at 25 C should be 60 C or lower at 240VDC.Here are some tips for thermal management.
1. Lower the primary switching frequency to lower MOSFET conduction loss and TRF copper loss.
2. If the LYT6079C is located at the bottom of the transformer, Elevate the transformer a little to minimized heat on the IC. Use bifilar or trifilar transformer to further reduce the heat cause by transformer.
3. Relocating the IC away from the bottom of the transformer would help reduce the thermal if your PCB have enough space.
4. Enlarge source copper pad as much as Possible. Adding soldermask near the source pin copper pad has better thermal heatsinking.
5. Adding heat spreader on top of the IC would have better thermal performance. Please attached sample picture.