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UCC28700: Constant current control

Adrien Lombet
Prodigy 100 points

Part Number: UCC28700
Other Parts Discussed in Thread: UCC28C43, TINA-TI

Hi,

I'm trying to do a circuit where a pwm controls current through a transformer where the mosfet is turned off when a given current is reached and is turned on back regulary. So basically a pwm where the duty cycle is adjusted to get a constant current peak in a transformer. 

The basic principle is shown below :

I was thinking about the UCC2870x, but I don't know if I can use it this way, I also saw others IC like UCC2863x or UC184x that might do the trick but I'm afraid to miss something . There is no voltage regulation whatsoever and I need to be able to disable the switching if needed

  • 0
    TI__Intellectual 2790 points

    Hi Adrien,

    I suggest looking into UCC28C4X controllers for an open-loop control system. UCC28700 or most of our ACDC controllers cannot run in open loop.

    Thanks, 

    Claire

  • 0 in reply to Claire Chang
    Prodigy 100 points

    Hi, 

    UCC2863x and UC184x looks to be more or less the same at least in the functional block diagram can you confirm if UC184x can also be used in open loop? 

    It's not really clear to me how I should connect the comp and fb pins I'm not sure to understand the datasheet, is the following configuration ok for the application described here above ?

    Moreover, is it possible to adjust the 1V threshold of CS using said pins ? It's looks like it could be possible but again it isn't clear to me

    Even if it's a simulation schematic, like always spice doesn't converge so I can't say if it's ok or not

    Regards,

    Adrien

  • 0 in reply to Adrien Lombet
    TI__Intellectual 2790 points

    Hi Adrien,

    I have assigned this post to an expert that can help answer questions regarding UCC28C4x and UC148X, he will respond within 1-2 business days.

    Thanks in advance.

  • 0 in reply to Claire Chang
    Prodigy 100 points

    Thank's a lot Claire !

  • 0 in reply to Adrien Lombet
    TI__Genius 10945 points

    Hello Adrien,

    You should be able to use the UCC28C4x in an open loop flyback. Have you tried simulating with PSpice? PSpice is a free simulation software that is designed for TI products. TI does not support LTspice simulations so we recommend using PSpice instead. We also have the TINA TI spice based software available. The models should be preloaded but if not, you can find PSpice and TINA TI models on the UCC28C4x website. 

    I have a steady state simulation of the UCC28C43 in a similar open loop configuration to what you have below. 

    Regards,

    Jonathan Wong

  • 0 in reply to Jonathan Wong
    Prodigy 100 points

    Hello Jonathan,

    I tried with tina and that might be ok. Do you think there's a way to change the 1V trigger limit of CS ? 
    By the way, I think the circuit you posted might not work since OUT is connected to VCC which is at 100V and even if there's a resistor divider, the charges on the decoupling cap should take the VGS beyond it's limit but I might be wrong

    Best regards,

    Adrien

  • +1 in reply to Adrien Lombet
    TI__Genius 10945 points

    Hello Adrien,

    PSpice is the newer software but TINA-TI should work as well. The PSpice model is unencrypted so you will be able to modify the model. You cannot externally change the CS threshold but you can set up COMP differently so that the CS equivalent threshold can be changed. You can view the block diagram below from page 13 of the datasheet.

    OUT can be higher than the MOSFET VGS if the MOSFET model allows it. You can try adding clamping to VGS or use another MOSFET model with a higher VGS.

    Regards,

    Jonathan Wong