What this MC34063 calculator does
The MC34063 is one of the most widely used classic DC-DC converter ICs. It can build a buck, boost, or inverting regulator with only a handful of external parts. This calculator gives you a quick first-pass design by estimating key values such as duty cycle, on-time, off-time, inductor value, current-limit resistor, timing capacitor, and feedback divider.
It is designed for practical bench work: fast estimates, then refine with the datasheet, component tolerances, thermal checks, and real measurements.
How to use it
1) Select topology
- Buck: Output voltage lower than input voltage.
- Boost: Output voltage higher than input voltage.
- Inverting: Negative output rail (enter magnitude in the form).
2) Enter electrical targets
Input voltage, desired output voltage/current, and switching frequency determine the stress on the inductor, switch, diode, and capacitor. Start with realistic numbers from your source and load, not ideal lab values.
3) Review computed component values
- Ton / Toff: Helps verify duty cycle is sensible.
- Inductor estimate: Starting point for selecting a standard value.
- Rsc: Sets switch current limit using the MC34063 current-sense pin.
- Ct: Timing capacitor estimate from on-time.
- R1/R2: Feedback network estimate for voltage setting.
Design notes for better real-world performance
Keep the switch loop compact
Route high-current switching loops as short and wide as possible. A compact loop reduces EMI, ringing, and unexpected losses. Place the diode, switch path, and inductor physically close.
Use appropriate inductor current rating
The inductor must tolerate peak current without saturation. Always choose a saturation current comfortably above computed peak current. A saturated inductor can collapse regulation and overheat components quickly.
Choose diode type carefully
A Schottky diode is typically preferred for low forward drop and fast switching. This improves efficiency and reduces heat, especially in boost and inverting configurations.
Common mistakes to avoid
- Using a duty cycle too close to 100%, leaving no control headroom.
- Ignoring switch saturation voltage and diode drop in early calculations.
- Picking an inductor only by nominal inductance, not by saturation current and DCR.
- Undersizing the output capacitor ripple current rating.
- Skipping thermal checks on the IC and diode at maximum load.
Quick validation checklist before prototyping
- Verify operating point over input-voltage range (min to max Vin).
- Check peak switch current against MC34063 limit and thermal budget.
- Confirm inductor saturation margin and temperature rise.
- Confirm output ripple meets target with selected capacitor ESR.
- Measure efficiency and switch waveform on scope under full load.
This calculator is intentionally simple and fast. For final design release, validate with the MC34063 datasheet, real component models, and lab measurements across process, voltage, and temperature.