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Ryan
Ryan
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This is a pretty common formula used for calculating what the output inductor value should be. There’s a few design considerations that come into choosing an inductor value.

  • Size
  • Cost
  • Output ripple current (so you’re operating in CCM during nominal operation).
  • Output ripple voltage.

The inductor controls the output ripple current of the converter. The higher the inductance value, the lower the ripple will be. If the ripple amplitude is greater than the output current, your converter will operate in discontinuous conduction mode (DCM) to try to maintain the output voltage, but this will affect the stability and efficiency of the converter. In most applications you want to avoid this.

It’s common practice to choose the ripple current to be around 10-40% of the maximum DC output current. This way you don’t usually use a bigger inductor than you need, but you’ll usually be operating in continuous conduction mode (CCM). Once you have this value it’s a good idea to rerun the calculation with \$I_O\$ as your minimum expected operational current and make sure the output ripple current ratio is less than 200%. That way you make sure you stay in CCM during operation.

Another reason to have a larger inductor is because it lowers your output ripple voltage. Your output capacitors also affect this, so there’s usually a trade off between capacitor size and inductor size to find a good balance to get the output ripple voltage within spec.

For your case I would probably choose the smallest inductor you can that would keep the converter in CCM under most operational cases and then pick capacitors to reduce the output ripple to where you want and keep the output stable. Once you have a good value you can choose an inductor that has reasonable DC resistance and make sure the max saturation current is belowgreater than the maximum DC output current plus the output current ripple amplitude.

I would also simulate the design once I was done to double check it will behave the way I expect. You can use the free TINA-TI Spice simulator to simulate TI’s parts.

This is a pretty common formula used for calculating what the output inductor value should be. There’s a few design considerations that come into choosing an inductor value.

  • Size
  • Cost
  • Output ripple current (so you’re operating in CCM during nominal operation).
  • Output ripple voltage.

The inductor controls the output ripple current of the converter. The higher the inductance value, the lower the ripple will be. If the ripple amplitude is greater than the output current, your converter will operate in discontinuous conduction mode (DCM) to try to maintain the output voltage, but this will affect the stability and efficiency of the converter. In most applications you want to avoid this.

It’s common practice to choose the ripple current to be around 10-40% of the maximum DC output current. This way you don’t usually use a bigger inductor than you need, but you’ll usually be operating in continuous conduction mode (CCM). Once you have this value it’s a good idea to rerun the calculation with \$I_O\$ as your minimum expected operational current and make sure the output ripple current ratio is less than 200%. That way you make sure you stay in CCM during operation.

Another reason to have a larger inductor is because it lowers your output ripple voltage. Your output capacitors also affect this, so there’s usually a trade off between capacitor size and inductor size to find a good balance to get the output ripple voltage within spec.

For your case I would probably choose the smallest inductor you can that would keep the converter in CCM under most operational cases and then pick capacitors to reduce the output ripple to where you want and keep the output stable. Once you have a good value you can choose an inductor that has reasonable DC resistance and make sure the max saturation current is below the maximum DC output current plus the output current ripple amplitude.

I would also simulate the design once I was done to double check it will behave the way I expect. You can use the free TINA-TI Spice simulator to simulate TI’s parts.

This is a pretty common formula used for calculating what the output inductor value should be. There’s a few design considerations that come into choosing an inductor value.

  • Size
  • Cost
  • Output ripple current (so you’re operating in CCM during nominal operation).
  • Output ripple voltage.

The inductor controls the output ripple current of the converter. The higher the inductance value, the lower the ripple will be. If the ripple amplitude is greater than the output current, your converter will operate in discontinuous conduction mode (DCM) to try to maintain the output voltage, but this will affect the stability and efficiency of the converter. In most applications you want to avoid this.

It’s common practice to choose the ripple current to be around 10-40% of the maximum DC output current. This way you don’t usually use a bigger inductor than you need, but you’ll usually be operating in continuous conduction mode (CCM). Once you have this value it’s a good idea to rerun the calculation with \$I_O\$ as your minimum expected operational current and make sure the output ripple current ratio is less than 200%. That way you make sure you stay in CCM during operation.

Another reason to have a larger inductor is because it lowers your output ripple voltage. Your output capacitors also affect this, so there’s usually a trade off between capacitor size and inductor size to find a good balance to get the output ripple voltage within spec.

For your case I would probably choose the smallest inductor you can that would keep the converter in CCM under most operational cases and then pick capacitors to reduce the output ripple to where you want and keep the output stable. Once you have a good value you can choose an inductor that has reasonable DC resistance and make sure the max saturation current is greater than the maximum DC output current plus the output current ripple amplitude.

I would also simulate the design once I was done to double check it will behave the way I expect. You can use the free TINA-TI Spice simulator to simulate TI’s parts.

Source Link
Ryan
Ryan
  • 2.4k
  • 8
  • 17

This is a pretty common formula used for calculating what the output inductor value should be. There’s a few design considerations that come into choosing an inductor value.

  • Size
  • Cost
  • Output ripple current (so you’re operating in CCM during nominal operation).
  • Output ripple voltage.

The inductor controls the output ripple current of the converter. The higher the inductance value, the lower the ripple will be. If the ripple amplitude is greater than the output current, your converter will operate in discontinuous conduction mode (DCM) to try to maintain the output voltage, but this will affect the stability and efficiency of the converter. In most applications you want to avoid this.

It’s common practice to choose the ripple current to be around 10-40% of the maximum DC output current. This way you don’t usually use a bigger inductor than you need, but you’ll usually be operating in continuous conduction mode (CCM). Once you have this value it’s a good idea to rerun the calculation with \$I_O\$ as your minimum expected operational current and make sure the output ripple current ratio is less than 200%. That way you make sure you stay in CCM during operation.

Another reason to have a larger inductor is because it lowers your output ripple voltage. Your output capacitors also affect this, so there’s usually a trade off between capacitor size and inductor size to find a good balance to get the output ripple voltage within spec.

For your case I would probably choose the smallest inductor you can that would keep the converter in CCM under most operational cases and then pick capacitors to reduce the output ripple to where you want and keep the output stable. Once you have a good value you can choose an inductor that has reasonable DC resistance and make sure the max saturation current is below the maximum DC output current plus the output current ripple amplitude.

I would also simulate the design once I was done to double check it will behave the way I expect. You can use the free TINA-TI Spice simulator to simulate TI’s parts.