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Capacitor Charger

Danilo A.
Mastermind 28590 points
Other Parts Discussed in Thread: LM5022

Hi Team,

A customer is looking for a flyback capacitor charger to charge a 4uF capacitor to 450V in a time of approximately 1ms. The input voltage is from a 12V battery but some cars use 16V battery. The device will be use to make a CDI ignition system for racing cars. The customer is looking for a similar product to LT3750 from Analog Devices. Do we have a similar solution?

Regards,

Danilo

  • 0
    TI__Intellectual 2640 points

    Hi Danilo! 

    Thanks for reaching out! Check out this reference design here! It is a little slower than your requirement, but also charging a much larger capacitor. It uses the LM5022 device as a controller. 

    Thanks again for getting in touch, I hope this information helps! 

    Aidan

  • 0 in reply to Aidan Davidson1
    TI__Mastermind 28590 points

    Hi Aidan,

    Is it safe to increase the transformer ratio and change some passive components to achieve a 450VDC output?

    Regards,

    Danilo

  • 0 in reply to Danilo A.
    TI__Intellectual 1235 points

    Hi Danilo,

    You probably don't need to change the transformer turns ratio. The primary inductance is 5uH and turns ratio is 1:6 so it runs CCM during charging but DCM in steady state. More important are the device ratings, such as the 500V output capacitor, compensation capacitor and secondary soft-start capacitor. The average output current during charging is 0.8 A, but the primary peak current is on the order of 40A. You will need to maintain the same charge balance during startup given by C*V=I*T. So 4mF*400V/0.8A=2sec. If you try to exceed the 0.8A average output current during charging, you will overload the the primary. For your application 4uF*450V/0.8A=2.25ms. That is as fast as you can charge the output capacitor without exceeding the primary current capability of the design. You adjust the secondary soft-start by changing the value of C14, which is now 0.22uF. Steady state output power is limited to around 40W.

    Best Regards,

    Bob Sheehan

    Power Design Services

  • 0 in reply to Bob Sheehan
    Prodigy 10 points

    Hello Bob. I am Gastón from Argentina. 

    How can a reach 1ms (or at least 1.5ms)? Changing the transformer could be the aswer? 


    Best Regards

  • 0 in reply to Gaston Fabbietti
    TI__Intellectual 1235 points

    Hi Gaston,

    You will need to double the power capability of the design, which includes the transformer, MOSFET and all power stage components.

    Best Regards,

    Bob