This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TIDA-010062: switching freq

Part Number: TIDA-010062
Other Parts Discussed in Thread: PMP20978,

Hi,

 

We are aiming at 96+% efficiency for PFC+LLC at 750W.

The design has tight spacing requirements ~ 45W/in3 for the inner room.

The casing is designed to dissipate 30W with a 30~35 deg. temperature rise.

 

Starting with the LLC, is 1MHz switching frequency achievable?

Plan to use GanFET for switching devices and SR.

From other designs like  PMP20637 / PMP20978, I see that a dead-time control for SR is implemented.

I guess it is necessary? How could it be implemented with the MCU solution?

Can TMS320F28002x MCU be used for that implementation (48-pins package).

 

For the PFC stage.

Apart from MIPS power and magnetic design, is there any parameter that could limit the switching frequency (ZVS? spike?)

Using the CCM totem pole design of TIDA-010062, can a 500KHz switching frequency be achievable with a 98% PFC efficiency?

 

Thank you

David

  • Hi David,

    Before answer your questions, several questions need you clarify in first:

    • What is the input voltage of the efficiency you want?
    • The efficiency is your target, or keeping thermal rise is your target?
    • What is your efficiency target for LLC stage?
    • How large volume you want to give it to the LLC stage?
    • How large CHOKE you want to use in the PFC stage?
    • What kind of SR logic you will to use for the LLC stage?
  • Hi Dyson,

     

    What is the input voltage of the efficiency you want?

                 Assume at 230Vac.

                 The design shall operate from 100Vac~265Vac

     

    The efficiency is your target, or keeping thermal rise is your target?

                 To me, they are both linked.

                 Higher efficiency means lower losses, which means less temperature rise.

                 The design shall use natural air convection for cooling.

                 The casing is entirely made of aluminum and serves as the heatsink.

                 The design shall operate from -30/+70 deg

                

    What is your efficiency target for LLC stage?

                 At the moment I assume 98% efficiency for LLC and 98% for PFC

                   

    How large volume you want to give it to the LLC stage?

                 <75 cm3, excluding the heatsink,

                 10 cms (L) x 5 cms (W) x 1.5 cms (H) at most

                 To ease thermal dissipation, I plan for a slim/flat PCBA design, so I can use more surfaces to conduct heat out.

                                    

    What kind of SR logic you will to use for the LLC stage?    

                 If you mean voltage, 5V or 10V

                 For topology, half-bridge should get better dissipation (as long the winding are kept as short as possible)

                 For technology, GanFET with dedicated gate drivers is considered.

     

    David

  • Hi David,

    Sorry for late by Chinese new year holiday.

    First answer your earlier question, your size is really very tight, and TI GaN will help you achieve higher efficiency.

    But, I don't think you need to use as high as 1MHz, so high switching frequency will significantly reduce your efficiency. The power loss is not only dominated by the switches, but also the core loss,  the proximity effect of windings, and the conducting resistance of the SR FET. 

    For the PFC stage, its power loss at 100Vac will be much higher than 230V. If you want to keep the thermal rise, you need take the 100Vac full load condition into consideration, other than 230V. And it is hard to achieve 98.0% at 100Vac input, even using GaN FET. Reducing the switching frequency can help you to get higher efficiency, but you will scarify more space for the PFC choke increasing. This need your carefully balancing and trade off between the size and the power loss.

    In a word, your spec is not an easy work, and it is hard to answer with an simple words. I suggest you to reach out an professional team for this task, or TI FAE's help.