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UC1825: INPUT POWER TO TANSFORMER

PONJOTHILAKSHMI RAJALINGAM
Prodigy 80 points
Part Number: UC1825
Other Parts Discussed in Thread: UC3825, TINA-TI

How to input power to an ideal transformer since i need to control output voltage of a buck converter. i am using uc1825 for pwm generation. I am using transformer to step up down the input ac voltage.

  • 0
    TI__Mastermind 21075 points

    You mention "How to input power to an ideal transformer" - are you referring to a simulation? I do not understand exactly what is being asked - can you please provide more information and maybe a top level schematic or sketch?

    Regards,

    Steve

  • 0 in reply to Steven Mappus1
    Prodigy 80 points

    UC3825.TSC

    Sir i want a closed loop control of this simulation. But i cannot achieve this. Even after the EA becomes zero, still i get output pulses from UC3825, so I cannot control the output. Also i need to input the power value for the transformer used in this file.  For eg, to get 100V at end, voltage at non inverting terminal be 445.76mV. After reaching 100V, my EA was zero, but still i get output beyond 100V.

  • 0 in reply to PONJOTHILAKSHMI RAJALINGAM
    TI__Mastermind 21075 points

    Hi,

    The simulation file you attached seems to missing some critical components/connections. What are the design parameters you are trying to simulate? 

    Steve

  • 0 in reply to Steven Mappus1
    Prodigy 80 points

    V0=500v, Vin=12v, Np/Ns=1/92,I0=4.5A I need to control the output voltage. For 500V at output, Vref is 2.31V(voltage at non inverting terminal of uc3825).  Clock frequency is 40kHZ, switching frequency is 20kHZ. Tperiod=50us, Ton=22.5us.(Dc to DC)

  • 0 in reply to PONJOTHILAKSHMI RAJALINGAM
    TI__Mastermind 21075 points

    Hi,

    You appear to have set up the UC1825 in voltage mode which requires a Type 3 compensator but you are using a Type 2 compensator (Current Mode Control). You have applied the full ramp to the PWM comparator, non-inverting input but the inverting input (EA out) is 0V? The EA output is 0V because there is 0V applied to the NI input of the voltage error amp, yet you are using a voltage divider from the secondary that expects to see 2.3V when VOUT=500V? Also, there is no output inductor and the gate drive to the primary MOSFETs is only 5V, barely enough to turn them on (but maybe ok for simulation). The topology you have designed is a unconventional compared to the way we typically configure the UC1825 for a push-pull converter topology - I'm wondering if this was done on purpose? It seems you are trying to operate two independent power stages interleaved but you would need an LC filter on the output and a way for the secondary current to freewheel in each leg during the off time. Also the design parameters you mentioned suggest 2.25kW output power and transformer turns ratio of 1:92, which easily results in more than 200A seen on the primary - is this what you expect? I would start by adding 2.31V to the NI input of the error amp and then double check to verify the topology and especially secondary side current flow.

    Regards,

    Steve

  • 0 in reply to Steven Mappus1
    Prodigy 80 points

    Yes sir you are right. We took this example from TI,they done it for push-pull. We want 12V to 500V output ful bridge.but we simulated only half bridge. Also we need both current and voltage control,we started with voltage control first.

  • 0 in reply to PONJOTHILAKSHMI RAJALINGAM
    Prodigy 80 points

    Also, we designed a transformer for 1100V. we need to get 100V to 1100V output. Based on that we need to control voltage and current. we removed the output inductor,since we don't need any inductor at output.Instead wee use load resistor of 110ohm.

  • 0 in reply to PONJOTHILAKSHMI RAJALINGAM
    TI__Mastermind 21075 points

    Hi Given,

    Perhaps you started with UC1825 because you saw an app note/ref design/Simulation model but now that you have described a bit more about your design goals, I don't think the TINA-TI model for UC1825 is going to get you there. For the power level and control you are interested in, I would suggest UCC28950 which is a phase-shifted full bridge controller with SR control. The UCC28950 has a strong history as an industry standard, high power controller and within the product folder you will see lots of helpful app notes, design guides, EVM hardware and TINA-TI sims. Thanks for using the TI e2e forum and if you need additional support, please open a new thread.

    Regards,

    Steve

  • 0 in reply to PONJOTHILAKSHMI RAJALINGAM
    TI__Mastermind 21075 points

    Thank you - I am closing this thread but if you still need help, please open another discussion thread?