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[LM5021]110V input isolated DCDC converter

Tomoaki Yoshida
Expert 2200 points
Other Parts Discussed in Thread: LM5021

Hi

 

I am considering the DCDC converter in the specification such as the following.

Vin max : 110V

Vout : 5V

Iout : about 200mA

 

Since 110V input of, initially I had been examined UCC289x, I found the PMP8657 in the reference design on homepage.

PMP8657 uses the LM5021 in Vin70V.

Output voltage is 7V, current is 0.45A in PMP8657 and it is close to my examination.

 

I'm going to consider the system of 110V input based on the PMP8657.

How can the possible design man-hours and cost hopes to reduce, is there no problem to be changed to 110V input?

Or is it better using UCC289x in which it can be entered the 110V direct?

If there is any advice, please tell me.

 

Thanks.

  • 0
    Genius 3295 points

    Hello Tomoaki,

    I would advise you not to use this design for a 110V application.  The 70V input is DC for one and secondly, this is  worst case, high line voltage. The design is optimized for a nominal DC voltage of 48V. For a 110V application I assume you mean 110 VAC. In this case you would need a rectifier and EMI filter.  In addition, you would need to replace the transformer, the snubber network, and the MOSFET and possibly the compensation network for this EVM to work at a regulated 110VDC. If my assumption that you need a 110VAC is correct,  you need a transformer that is optimized for 110V turns ration and can sustain voltage excursions of at least 90 VAC to 130 VAC.

    Follow this link for your design:

    http://www.ti.com/tool/PMP5192?keyMatch=null&tisearch=tidesigns-power

  • 0 in reply to Chuck Sampson
    Expert 2200 points

    Hello Chuck,

     

    Thank you for your reply.

    I'm sorry my explanation was not enough.

    Input voltage is DC and nominal 90V, max 110V.

    I don't think that I can use as it is the design of the PM8657.

    However, since such as close to my specifications, I thought taht what may be changed this design to the base.

     

    In the same circuit configuration, can it correspond to 100V input?

    Offcourse I will change circuit constants.

    Since I had originally discussed UCC289x, I want to know is better here in the circuit there is an advantage.

    Since UCC289x is capable of 110V input, the curcuit I'm wondering slightly simple.

     

    Thanks

    Tomoaki Yoshida 

  • 0 in reply to Tomoaki Yoshida
    Genius 3295 points
    Tomoaki,

    Okay, sorry for the confusion. For a 5V 0.2A, and 1W application, I wouldn't use the UCC289x unless I needed greater than 90% efficiency. And I don't see any advantage of the UCC289x over the LM5021 for you application. In fact the UCC289x requires an additional SR circuit. The lm5021 can work at 110Vs. The only constraint is that you need to keep the bias, or the current going into the Vin pin less than 5 ma. The IC contains a zener that clamps the input voltage to 36V. The LM5021 design is set for 400 uA bias current. At 110V you need to check to see if that is enough current to drive the main MOSFET. If it's not, then you have to reduce the value of resistors R2 and R3. You will probably need to change out the MOSFET since it's drain to source voltage maximum is only 150 V. You will need to change out the transformer to get 5 Vs out unless you are thinking of using a linear to buck down the 7 volt output to 5 V. Also your ripple current and ripple voltage will be high unless you re-design the transformer. With a 5 V output instead of 7 v output your dc gain is different so you need to verify that your loop gain is okay. If you redesign the main transformer, your leakage inductance changes -so your clamp circuit may need to be changed. The closet reference design I could find is the PMP4650. It has a 12V output with a 130 V maximum input. You could use a low power, drop in 12 to 5 V dc-dc on the output to save engineering time and effort.