• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 63 subscribers
  • Views 563 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

MC33063A

Lucas Prilenski
Prodigy 10 points
Other Parts Discussed in Thread: MC33063A

Hello,

   I designed a SMPS power supply using the MC33063A component, I need to supply 40 volts and 1 amp to the load. However, the datasheet says that Ipk cannot exceed 1.5A. When I calculate Iout to be 1 amp, I found Ipk to be 2.66 A. I decided to use the configuration shown in figure 5A of the datasheet to surpass this limit. My question is, how do I calculate the value of the resistor that is connected to pin 2 and the base of the external BJT? Also, I am going to be making a lot of these devices and would really appreciate it if someone would be able to verify that I did this the right way. I've attached a page that includes the values that I calculated and the way that I made the connections.

Thanks a lot!

Lucas





  • 0
    TI__Mastermind 24975 points

    Hello Lucas,

    The idea behind that resistor is that it pulls the base low when the output turns off. The transistor has a capacitance associated with it and the resistor helps to discharge the capacitance of the transistor. The capacitor will discharge more quickly if the resistance is lower as it can pull more current to ground more quickly.

    100 Ohms is a good starting point for this resistor, but lower values will turn the switch turn off more quickly.

    As for your circuit. In general your circuit connections look good, however, I didn't necessarily go through and recalculate all of the values. Certainly I would double check the calculations and get a test board in to verify that the performance meets your specifications before committing to building a lot of these devices.

    Best,
    Michael