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TPS23730EVM-093: Duty Cycle

Michael Jeong1
Expert 2630 points
Part Number: TPS23730EVM-093
Other Parts Discussed in Thread: UCC2897A, , PMP23253

Hello Expert,

Our customer is designing POE PD BT circuit which is configured with TPS2373-4 and UCC2897A.

In the case of FORWARD CONVERTER, I know that MAX DUTY should not exceed 50%.

They have made the board by referring to the transformer of TPS23730EVM-093.

But, we observed that the duty was occurred up to about 63% as shown below.

Is there able to occur some issue? or Is it OK?

Could you please review and give me feedback?

Also, we need to review their schematic and don't share on this thread.

Could you reply to me by e-mail and then I will send it.

My e-mail : michael.jeong@arrow.com

=============================================

PWM frequency : 205KHz
Input : 41VDC
Output : 12V/6A (72W)
Transformer : EFD25, turn ratio 2:1 (L value about 100uH)

=============================================

Best regards,

Michael

  • 0
    TI__Mastermind 37121 points

    Hi Michael,

    Thanks for reaching out to us!

    You are right that TPS23730EVM-093 applied active clamping forward (ACF) converter. The output voltage Vout = (Nsec/Npri) * D * Vin. For PoE Vin is 37-57V. The duty cycle D could exceed 50% at some conditions. In your case it could be 12 V = 41 * 1/2 * 0.59, where D = 59%. 

    Below is an example of primary MOSFET Vds of PMP23253 with ACF and Npri/Nsec = 1.33:1. (https://www.ti.com/lit/ug/tidt313/tidt313.pdf?ts=1669147517926). At 37-V Vin its duty cycle exceeds 50%.

    I will reply you for the schematic by email. We are going to have Thanksgiving days soon so it may take longer time for sending you review back. 

    I will close this thread for now as we have connected in email and the duty cycle question was answered. Please open a new thread if you have any further questions.

    Best regards,

    Diang