TPS92510 issues

Roger Ding

Other Parts Discussed in Thread: TPS92510

Hi,

there is a question inSchnieder for TPS92510. they do some test with our EVM.

and they get some waveform. please see attached waveform.

The oscillogram of LED driver as following,

1. Normal oscillogram

Test condition: Vin= 42Vdc; Vout= 19.2Vdc; Io=700mA; Fsw= 350Khz (Loading is 14W LED downlight)

2. Failure oscillogram

Test condition: Vin= 24Vdc; Vout= 19.2Vdc; Io=700mA; Fsw= 350Khz (Loading is 14W LED downlight)

In this test condition, The LED downlight has slightly flickered at the brightness dim down to 10%, and you cold see a wide duty in the waveform.

customer use the input voltage is 24V, which always is slight flicker. do you have some method to improvement.

Channel 2 : Voltage of PH pin to GND, Channel 4: output current.

over 11 years ago

0 Mike Kosteva over 11 years ago

TI__Intellectual 2590 points

Has the customer made any changes to the EVM to work at 24 VDC in? The current versions turn on is approximately 42 vdc so it would need a change to work at 24 vdc. What is their PWM frequency?

0 Roger Ding over 11 years ago in reply to Mike Kosteva

TI__Intellectual 1720 points

the prototype of customer is 24V input voltage, and there is slight flick in small width of PWM dimmer. thus we modify our EVM for 24V input, only change the value of resistor connect to EN pin. all other part isn't be modified. we find our EVM is same with customer board with 24V input voltage. there is a wide duty before the peak output current, there is alway flick in small duty of PWM dimmer.

could you help to anylize the reason?

0 Mike Kosteva over 11 years ago in reply to Roger Ding

TI__Intellectual 2590 points

Was R4 and R6 values changed? These are usually changed in pairs to maintain hystersis. Also the new turn on voltage must be set higher than the LED string voltage otherwise the output will go to maximum duty cycle before the LEDs conduct which can cause flicker. What are the value changes and again what is the PWM frequency?

The values of R4 an R6 should be calculated using the TPS92510 spreadsheet available on the WEB. If the string voltage is 19 volts the turn on voltage should be calculated for a turn on of 21 to 22 vdc.

0 Roger Ding over 11 years ago in reply to Mike Kosteva

TI__Intellectual 1720 points

Pls see the schematic of the demo board, R4 value is 510K, R6 value is 30K. PWM frequency is 1000 Hz.

0 Mike Kosteva over 11 years ago in reply to Roger Ding

TI__Intellectual 2590 points

Please have them try values R1=Rent=165k and R2=Renb=9.76k. This sets startup at 22v dc and shutdown at 21 vdc.

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TPS92510 issues