MC34063 Universal Calculator: Step-by-Step Design for Common Voltages

MC34063 Universal Calculator: Quick DC‑DC Design Tool for Boost, Buck, and Inverting Circuits

What it is

• A simple design utility (web or spreadsheet) that uses MC34063 datasheet formulas to compute component values for buck, boost, and inverting topologies.

Why use it

• Fast: converts input/output specs and desired ripple/frequency into Ct, L, Rsc (current sense), Cout, feedback resistors, and switching duty.
• Educational: shows how MC34063 timing and current‑limit constraints affect choices.
• Practical: helps pick standard component values (inductors, Schottky diodes, caps) and suggests when an external pass transistor is needed for >~1 A.

Key formulas (from datasheet — implemented by calculators)

• Feedback: Vout = 1.25·(1 + R2/R1) → choose R1 then compute R2.
• Duty (for boost approximate): D ≈ 1 − Vin/Vout (used with timing to set Ton/Toff).
• Timing cap: Ct ≈ 4.0·10−5 · Ton (Ton from desired frequency and duty).
• Inductor (min): Lmin = (Vin − Vsat − Vout)/Ipk · Ton (topology signs change per mode).
• Current sense resistor: Rsc ≈ 0.3 / Ipk (trips at ~300 mV).
• Output cap (approx): Cout ≈ Ipk·(Ton+Toff)/(8·Vripple) (for chosen ripple).

Practical tips the calculator usually includes

• Use a Schottky diode (low Vf) for boost/inverting circuits.
• Aim for 20–40% inductor ripple current; compute Ipk = Iout + Iripple/2.
• If required output > ~1 A, add an external power transistor (PNP for buck boost configurations shown in references).
• Choose Ct for ~20–100 kHz switching; higher frequency reduces L/C size but raises switching losses.
• Select components with adequate voltage/current ratings and low ESR caps for stability.

Where to find one

• Manufacturer/app notes and online tools: TI app notes, hobbyist tutorials and MC34063 online calculators (examples: TI application notes, ElecCircuit, Jotrin MC34063 calculator, various blog/project pages).

If you want, I can run example calculations (pick topology, Vin, Vout, Iout, desired ripple and frequency) and give a complete parts list and values.