• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 633 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

UCC28950 30V -> 150V QD overheat

Vladimir Pimonov
Prodigy 170 points
Other Parts Discussed in Thread: UCC28950

Well, as i posted before (https://e2e.ti.com/support/power_management/isolated_controllers/f/188/t/438381),  i tried to make DC/DC 30V -> 150V using UCC28950.

After solving last problem with your help, i get new one - all works fine but QD (transistor D). When load is low (under 50W) all works fine, when load more then 50W QD start heat quickly... At half load efficiency is about 81% - its too low for this IC I think.

using reference design - slua560c and slura08

IC - UCC28950

drivers - IR2113S

Q - IRF3205

Have any idea?

  • 0
    Prodigy 170 points

    up

    still QD heats a lot....

  • 0 in reply to Vladimir Pimonov
    TI__Mastermind 25570 points
    Hello Vladimir

    I assume you are now working with a 150v input voltage ?

    Anyhow, normally what we would recommend is that you disable the Synchronous rectifiers. Remove their gate drives and tie the gates to 0V. Then look to see if the D FET still gets hot. Look at the voltage across the transformer primary and see if the system is achieving ZVS. Look for shoot through currents and adjust the DELAB, DELCD, ADEL resistors if necessary.
    Is the D fet getting a good gate drive signal?
    Is the D FET correctly attached to the heatsink (I hesitate to mention this because it's so obvious, but I've been caught out in the past)

    If the D FET looks ok, then re-connect the SRs and look for cross conduction in them. One caution, the diagram in the slura-08 document shows paralleled SR MOSFETS with common Source and gate connections - this is a bad idea because there are oscillation modes (HF oscillations around 100MHZ and higher) that can occur in MOSFETs paralleled in this manner. Solution is to use individual gate drive resistors for each device - this normally suppresses the oscillations.

    Let me know how you are getting on.
    Colin
  • 0 in reply to Colin Gillmor
    Prodigy 170 points
    Nope ))
    Vin = 30 V
    Vout = +/-75 V dual rail with center. no Synchronous rectifier, diodes only, because of low current (2A)
    No Ls because of output bridge topology with no back energy
    No heatsink for now - i mesure temperature of each transistor separately and QA QB QC stay cool at 120 W load but QD heats a lot
    signals ok, trying differnt filters of feedback loop - nothing good - calculated is best.

    QD switchs with no zvs function, dont know why, but last idea that QD is the only transistor that MUST switch with no ZVS...
    Am I right or not?