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For a circuit I'm designing, I want to use an MC34063AL-D08-T DC/DC converter (or a similar one; I just need a through-hole package) as a boost converter to boost a voltage Vin = 3.3-4.2 V (coming from a Li-ion battery) to a stable output of Vout = 5 V, with Iout = 250 mA.

I'm quite new to electronics and circuit design and I have no experience working with buck-boost converters, so I have been studying the datasheet, and the examples provided in it, in order to understand which components I'll need for my use case.

The issue is that the provided examples don't make sense to me. Here is the boost converter schematic provided in the datasheet:

Boost converter

If I try to use the calculation table provided at the end of the datasheet, the component values don't match the ones shown in the schematic above.

calculation table

For example, the datasheet specifies that this configuration has a voltage ripple Vripple = 400 mV (highlighted). If I try to compute the Vripple using the same components as in the schematic, it works out to around 194 mV.

I can't seem to reproduce the schematic; using the same requirements (Vin = 12 V, Vout = 28 V, Iout = 175 mA), all the components turn out different from what is shown. What am I missing?

Note: the diode used in the schematic is a 1N5819; I assumed a forward voltage of about VF = 0.45 V at a forward current of about IF = 250 mA. I won't use this diode, but the VF is needed to compute the duty cycle of the converter.

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  • \$\begingroup\$ ”all the components turn out different” Please show! \$\endgroup\$
    – winny
    Sep 8, 2022 at 12:26
  • \$\begingroup\$ @winny what do you mean? I will try to add an example in the post, but I just used the formulas provided in the table and used their Vin, Vout and Iout to compute the components. \$\endgroup\$
    – luigi
    Sep 8, 2022 at 13:52
  • \$\begingroup\$ Yes, please make a table. \$\endgroup\$
    – winny
    Sep 8, 2022 at 14:12

1 Answer 1

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Do you need something like this?

Included circuit in microcap v12.

enter image description here

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  • \$\begingroup\$ Well I didn't try simulating it, to me it seems more like I'm missing something about the design of this circuit. \$\endgroup\$
    – luigi
    Sep 8, 2022 at 13:53

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