Tool/software:
I want to confirm why the efficiency is so low during low load conditions
When Vout(+12V_D) no load, the temperature of PQ2306 is 70 °C
When I have load (3.3A) , PQ2306 is 97 °C
When no load,the measured current through PR2320 is 0.1A
When I have load (3.3A) ,the measured current through PR2320 is 0.8A
How can solve this issue?
Thanks
Hi Chen Lun Weng,
1. The PQ2306 is 29 mOhm MOSFET which normally has high switching loss and slow switching speed can cause shoot through. You can use a 50 - 75 mOhm MOSFET which normally has a better performance.
2. You may increase the PR2322 to 100kOhm to extend the deadtime. It may reduce the shoot through loss.
3. For improving the efficiency you can also consider changing the diode rectifier to half-FET rectifier, which may improve ~1% efficiency.
Best regards,
Diang
Hi,
I want to know why RDSON needs to be larger, I think the switching loss should be Qg smaller, can you explain more to me?
thank you
Hi Diang
How can I improve the efficiency between 0w and 30w? It seems that the measured efficiency value is lower than the spec.
thank you
Hi Chen Lun,
Thanks for your patience.
I saw your questions in email and Anthony was in the thread too. Would like to know if you still have concerns for efficiency? One thing could be related is the efficiency measurement with bench power supply could be with 4-pairs condition, where PR36 & 45 are shorted with +DC and PR12 &78 are shorted with -DC. If the measurement is under 2-pairs, the efficiency could drop a little.
PoE PD design power loss mainly are from the rectifier bridge, PD hotswap, and DC/DC. PD IC itself operating power is relatively low (for example, TPS23731 is 2.4mA x 57V = 136.8 mW max, by typical value it is < 100 mW).
May I know if the efficiency is with TI's EVM or with customer board. If with customer board, after adopting the half bridge rectifier and using a higher Rdson-FET?
Best regards,
Diang
Hi Diang,
The efficiency in the attached picture is our measured value, our board designed according to ti evm. We hope that the efficiency value at low load is as close as possible to the ti evm board efficiency value on the spec.(ex: 0.6A load we measured efficiency is 66%, but ti evm spec 0.6A load efficiency is 73%)
10am-6pm ok(UTC+8)
Hi Diang,
The efficiency in the attached picture is our measured value, our board designed according to ti evm. We hope that the efficiency value at low load is as close as possible to the ti evm board efficiency value on the spec.(ex: 0.6A load we measured efficiency is 66%, but ti evm spec 0.6A load efficiency is 73%)
10am-6pm ok(UTC+8)
Hi Diang,
I was measuring the Vgs value of PQ2306 and found that it exceeds the 20V specified in the Spec. The actual measured value is 24.24V, but the POE board still maintains Vout 12V. I would like to ask if there are any suggestions for improvement?
Hi Willy,
PQ2306 is the primary side NMOS. And its positive Vgs should be equal to VCC. The transformer is LDT8627 which has the same turns ratio between SEC and AUX winding. Theoretically VCC and positive Vgs should both be ~12V when Vout is 12V. Vout = Vin*Duty*Nsec/Npri, Vcc = Vin*Duty*Naux/Npri, and Naux = Nsec.
Can you doubel check the VCC and Vgs voltage. If the Vcc and Vgs are still high, it may be transformer is incorrect.
Best regards,
Diang
