TIDA-01505: current mode (CCM, DCM,..)

Paul, good morning.  We have received your query and forwarded it to our Automotive Systems team in Freising.  Please allow another day for Xun (Gong) to respond. 

Best Regards,

John Fullilove

Reference Design Operations

Texas Instruments

Hi Paul,

For this design when VIn reaches certain high level ~800V the converter runs into DCM. The majority of the time converter is running in CCM. The transformer primary side inductance is Lpri=1.5mH.

Hi Xun,

thanks for your answer.

Actually, my customer is designing a flyback with max output current of 0.4A and so the coupled inductor is operating in DCM almost all the time.

Ideally, he would need a primary inductance ten times lower. 

If customer wants to duplicate our design with no change, do you see any risk using the same design for a maximum output current of 0.4A ? 

best regards,

Paul Antunes 

Hi Paul,

For less current we have designed another revision of transformer with Coilcraft. Please see attached datasheet. Customer can apply samples to test it. This would work better. What is their input voltage range? The only problem I see could be the minimum on time.

ZB1285-AL.PDF

Xun,

Here are the key design inputs: Vin= 50V-1000Vdc; Vo= 15Vdc; Io=0.4A; Po=10W max

Hi Paul,

I would recommend using WA8537-BL (datasheet attached). The transformer would able to support such low current level with required minimum on time.WA8537-BL.PDF

Hello Xun,

Customer has another question about the stability of converter for high voltage and light current.

He thinks that the system is on DCM mode with voltage more than 100V and load of 0.3A. Is it right?

If the converter is designed in CCM mode for low voltage and high current, then does the stability of system can be guaranteed for high voltage and low current?

Hi Paul,

In general yes, if the compensation is tuned and the converter is stable at minimum Vin and maximum load condition. It will be stable at high Vin and all load conditions.