1. theoldwizard

    Thread Starter Member

    Jul 17, 2005
    As a first stage of a true sine wave inverter, I am looking at using the LM5032 dual switch mode controller. This IC has low input voltage shutdown, input current sense shutdown and output voltage PWM control.

    Typical application notes show it as dual current mode DC-DC boost converter, but it can be used in any PWM application with proper feedback. This app note thorough describes many of the design details. I also discusses continuous versus discontinuous mode.

    To achieve my goal, I need approximately 200V DC. I believe this could be easily be achieved by operating in discontinuous mode and using a step up transformer.

    This app note (page 23) and the circuit below, shows the IC used to step down high (36-78V) input DC voltage down to 12V with each half of the chip working independently. Unfortunately there is no accompanying circuit analysis so I am struggling.

    I know that T2 and its associated circuitry are used for input current sensing and could be replaced by a resistor network. L2 and L3 and C6-C10 are output filtering. The U3 is a comparator used to trigger the U2 opto-siolater for voltage feedback. A similar circuit would be required in my design.

    I guess my real question is the design criteria for transformer T1. The chip should be oscillating at a nominal 200KHz based on the value of R31. The transformer turn ratio obviously determines the resultant output voltage. Wire size corresponds to current. I would assume the transformer uses a toroidal form form but how do you size this ? Specifically resistance and inductance of the primary winding and size of the toroidal form.
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    If your running at high frequency between 100khz to 300khz, then you need flyback or smps transformers that are tuned to these frequencies like these or these