09H-13 – Buck (Step-Down) Converter (MC34063)

A compact boost converter design for efficient voltage step-down applications.

PCB Details

Part No: 09H-13

Title: Buck (Step-Down) Converter (MC34063)

Board Size: Approx. 50 x 50 mm

Pieces per Panel: 4

Panel Size: 100 x 100 mm (V-scored)

Schematic

Schematic

Board Layout

Top view of miniPCB

Circuit Description

This miniPCB implements a buck (step-down) converter built around the MC34063 controller (U1). The board accepts a DC input at P1-2/4 (V+) and delivers a lower regulated output at P1-5.

Typical use: stepping a higher DC supply down to a lower regulated rail for lab experiments or embedded projects. Select inductor value, diode type (Schottky recommended), and output capacitors according to desired load current and ripple performance.

Power Input & Filtering

  • C1, C2, C3 provide bulk energy storage and high-frequency bypassing for the input rail, reducing supply ripple and noise.
  • R1 is the current-sense resistor feeding the MC34063’s internal limiter to protect the switching transistor.

Switching Stage

  • The internal switch of U1 drives the main inductor L1, which stores energy during the on-time and releases it to the load during off-time.
  • D1 is the catch diode, providing a path for inductor current when the switch is off.
  • C5 is the primary output capacitor, storing charge directly from the inductor to supply the load during switching cycles.
  • C4 sets the MC34063’s oscillator frequency, determining the switching rate.

Output Filter

  • L2 acts as a ripple-reduction inductor, further smoothing current delivered to the load.
  • C6 is the secondary output capacitor, reducing residual voltage ripple and improving stability under load transients.

Regulation & Feedback

  • R2, R3 (potentiometer), and R4 form the voltage feedback divider that sets the output voltage; adjustment is made via R3.
  • LED1, with series resistor R5, provides a visual indication of output presence.

Connections

  • P1-1: Ground (GND) reference for input and output.
  • P1-2: Positive DC input (V+).
  • P1-3: No connection (NC).
  • P1-4: Positive DC input (V+), internally linked to P1-2.
  • P1-5: Regulated DC output (Vout).

Example Parts List

Ref Des Value / Part Rationale
C1 100 µF electrolytic Bulk input filtering to smooth supply transients.
C2 100 nF ceramic High-frequency bypass to suppress switching noise.
C3 100 µF electrolytic Additional bulk input filtering for stability.
C4 470 pF ceramic Oscillator timing capacitor setting switching frequency.
C5 330 µF electrolytic Output capacitor storing charge from the inductor to supply load current.
C6 330 µF electrolytic Secondary output capacitor for smoothing residual ripple.
D1 Schottky diode Freewheeling path for inductor current during switch-off.
LED1 Red LED Visual indicator of output voltage presence.
L1 220 µH Energy storage inductor for buck conversion.
L2 220 µH Ripple-reduction inductor for output filtering.
P1 5-pin right-angle header Main connection interface for input power, ground, and regulated output.
R1 0.33 Ω Current sense resistor for switch protection.
R2 2 kΩ Feedback divider upper resistor for voltage regulation.
R3 2 kΩ (3296W pot) Type 3296W multiturn potentiometer for adjustable output voltage.
R4 1 kΩ Feedback divider lower resistor for voltage regulation.
R5 1 kΩ Current-limiting resistor for LED indicator.
U1 MC34063 Switch-mode regulator IC controlling the buck topology.