BCR602 Liner LED Driver does not limit output current

[omerfaruk]

Hi,

Vin for MOSFET: 54V
Vcc for driver: 15V

I have tested BRC602 IC with IPD70R360P7S N-channel MOSFET to driver LEDs.

I have used 3x1.2R parallel resistor to get 0.4R resistance.

According to the formulation of the BCR602

0.4R=0.4V/I

Current (I) should be 1.0Amper...

But BCR602 driver does not limit the current. I have changed resistors and BCR602 IC with new ones (1.5R to get lower current), but the same problem.

By the way, PWM dimming is working. When I apply %20 dimming, I read 0.650A on the LEDs. Without dimming, I read 1.770A on the LEDs. (I think there is no limiter for current, but the power supply reduces the output voltage so I read 1.750A max, If I use a higher watt value power supply, I can read over 1.750A on the LEDs, because the driver does not limit the current.)

I read 0.051V on the Rsense resistors. 

Please check the schematic and photo. Need your support asap to produce PCB for a project. 

Thank you very much

Ömer Faruk

[omerfaruk]

Any one reply me? 

sorry for rushing. our gerber files are ready for production and need to order them if there is no design problem in my schematic. no have more time 😞

thanks for your support 

[AliAsgar]

Hi Omer,

Sorry for the delay in response.

The schematic looks fine. We suspect that there maybe some oscillations. Could you please probe the DRV and Vsense pins on an oscilloscope and let us know the behaviour of the signals?

Best Regards,
AliAsgar

[omerfaruk]

Hi Ali,

Thank you for your reply. I made a new single board (not multiple) test IC.

When I change the MOSFET, the current can be limited by IC. I think It was damaged.

With a 2R resistor, I have seen 200mA current, It is a true result. 0.4V/2R=0.2A

But now, we have another big problem. 

When I run the circuit, the MOSFET temperature is rising really fast. I measure temperature with the thermal camera about 120 Celcius in 10-15 secs after running the circuit. After 30-40 secs, Smoke comes out of the MOSFET.

Vin: 54V (Cin 910uF 100V)
VS: 15-16V (Cin 1000uF 35V + 100nF 50V)

Vout on LEDs: (11 serial Blue high power LEDs): 30-32V

I have measured Vsense, DRV, Vin, V on LEDs, VS with oscilloscope

DRV pin (LEDs ON)
DRV pin (LEDs OFF)
Vsense pin (LEDs ON)
Vsense pin (LEDs OFF)
Vin 54V
VS 15V
Voltage on LEDs (+ -)

Waiting for your help, thank you very much

[AliAsgar]

Hi,

What do you mean by Vin? Is it the Vds voltage of the mosfet?

Please try connecting the DRV to the gate of the transistor through a resistor.

Also please confirm if the temperature rise behaviour of MOSFET is seen for a constant 200mA of drain current.

Please check the datasheet of the MOSFET, the power handling capacity of the MOSFET and please confirm if it obeys all the parameters in the present system.

Best Regards,
AliAsgar

[omerfaruk]

Hello Ali,

I have tried a serial resistor but no positive effect.

I have found this:

LEDs use: 32V 0.2A = 6.4W (10 serial blue LED 3.2V)

When I drive with 54V, BCR602 circuit uses 0.2A current from the power supply. 

But when I drive with 35V, BCR602 circuit uses 0.2A current from the power supply as well.

54V: 54*0.2=10.8W
35V: 35*0.2=7.0W
LEDs: 6.4W

When I drive with 54V: 10.8-6.4=  4.4W of energy is consumed on the MOSFET. So the temperature is rising really fast. 

When I drive with 35V: 7.0-6.4=  0.6W of energy is consumed on the MOSFET. So the temperature is NOT rising.

As a result, when I increase input voltage, BCR602 does not reduce INPUT CURRENT. 

If I use low qty LEDs such as 5pcs (16V), 54-16= 38V, 38*0.2= 7.6W energy will be consumed on the MOSFET. 

The question is, WHY BCR602 does not reduce INPUT CURRENT when I increase INPUT VOLTAGE?

Waiting for your reply ASAP, please. 

[AliAsgar]

Hi,

Could you let us know the model of the MOSFET or if possible, share the datasheet of the same?

Could you try adding a resistor between MOSFET and Rsense resistor, in order to distribute the power?

Best Regards,
AliAsgar

[Michael_W · Accepted solution]

Hello Omer,

What you describe is exactly what BCR602 is expected to do and what it is made for: stabilize the LED current to a constant value determined by the resistor connected to VSENSE.

BCR602 doesn't have a function that reduces the current when input voltage is increasing. But such a function (or at least something similar) is implemented in BCR601: Active Headroom Control. Maybe you have a look at that device.
If BCR601 is not an option to you, you need to make sure that the difference between VIN and VLED is small enough that power can be dissipated by MOSFET.

You can as well think about attaching a NTC to MFIO and thermally couple it to the MOSFET. But finding the proper NTC may be tricky.

Best regards
Michael

[omerfaruk]

Hi 

I have shared the name of the MOSFET in my first post. It is infineon IPD70R360P7S (https://www.infineon.com/dgdl/Infineon-IPD70R360P7S-DataSheet-v02_02-EN.pdf?fileId=5546d462584d1d4a0...) 

Why i need to add resistor between MOSFET and Rsense to order distribute power ? If it is for protection of the MOSFET, why i waste my energy on the extra resistors with these methods. We want to increase efficiency....

I want to ask again "WHY BCR602 does not reduce INPUT CURRENT when I increase INPUT VOLTAGE?" Please check my last post again carefully. 

We must find real answer and solution.

I have shared all data but can not see valuable replies from your side. Time is limited for us for whole production but you are really slow.

Please be helpful for our problem to find solution. If possible discuss with other engineers. 

Please..,....,...

[AliAsgar]

Hi Omer,

Driver does not limit the current if the input voltage is increased. The driver will try its best to keep the output current constant.
Try using a MOSFET with a lower Rds such that the power dissipation of the MOSFET is as low as possible. Also we recommend you to use a heat sink with it as well.

Best Regards,
AliAsgar