The Original MC34063A 1.5A Step-Up/Down/Inverting Switching Regulator is a versatile monolithic DC-DC converter control integrated circuit manufactured by ON Semiconductor / STMicroelectronics / Texas Instruments. Encapsulated in an industry-standard DIP-8 through-hole package, it integrates all primary functions required for DC-DC power conversion on a single chip: an internal temperature-compensated reference, a controlled-duty-cycle oscillator with an active current-limit circuit, a driver, and a high-current 1.5A bipolar output switch. Operating across a wide input voltage range of 3.0V to 40V DC, the MC34063A can be configured into Step-Up (Boost), Step-Down (Buck), or Inverting (Negative Voltage) topologies using a minimal number of external components. It is widely used in automotive power adapters, portable electronics, battery-operated instruments, and embedded micro-power voltage rails.

Specifications

• Part Number / Model: MC34063A / MC34063AP1 (Commercial Temperature Range)
• Device Function: Monolithic DC-DC Converter Controller / Switching Regulator
• Package Type: DIP-8 (Dual In-Line 8-Pin Through-Hole, Plastic)
• Input Supply Voltage (Vcc): 3.0V to 40V DC (Absolute Max: 40V)
• Internal Switch Current Capability (Isw): Up to 1.5A Peak (Collector / Emitter)
• Feedback Reference Voltage (Vref): Typ. 1.25V / Range 1.21V to 1.29V (±2?curacy at 25°C)
• Oscillator Frequency Range: 100 Hz to 100 kHz (Determined by timing capacitor CT on Pin 3)
• Current-Sense Voltage Threshold (Pin 7 - Pin 6): Typ. 300mV / Range 250mV to 350mV
• Switch Saturation Voltage (Darlington connection, Pins 1 & 8 tied): Typ. 1.0V / Max. 1.3V (at Isw = 1.0A)
• Switch Saturation Voltage (Separate drive, forced beta): Typ. 0.45V / Max. 0.7V (at Isw = 1.0A, Idriver = 50mA)
• Comparator Input Bias Current (Pin 5): Typ. -40nA / Max. -400nA
• Quiescent Operating Current (Iq): Typ. 2.5mA / Max. 4.0mA (at Vcc = 5V to 40V, CT = 10nF)
• Total Power Dissipation (Pd): 1.25W (at Ta = 25°C in standard DIP-8)
• Operating Ambient Temperature (Ta): 0°C to +70°C
• Storage Temperature Range (Tstg): -65°C to +150°C
• Thermal Resistance, Junction to Ambient (Rth(j-a)): 100°C/W
• Pinout Configuration:
  • Pin 1: Switch Collector (Sw. Collector)
  • Pin 2: Switch Emitter (Sw. Emitter)
  • Pin 3: Timing Capacitor (CT)
  • Pin 4: Ground (GND)
  • Pin 5: Comparator Inverting Input (Feedback / FB)
  • Pin 6: Supply Voltage (Vcc / V+)
  • Pin 7: Peak Current Sense Input (I_pk Sense)
  • Pin 8: Driver Collector (Driver Collector)

Features

• Universal 3-in-1 DC-DC Topologies: Seamlessly configurable into Step-Up (Boost), Step-Down (Buck), or Voltage-Inverting (Negative Output) converter topologies with minimal passive parts.
• Wide 3V to 40V Input Range: Functions reliably across low-voltage battery rails up to high-voltage industrial and automotive 24V/36V systems.
• Integrated 1.5A Output Switch: Onboard NPN power switch and driver stage handle switch currents up to 1.5A peak without requiring external discrete power transistors.
• Cycle-by-Cycle Peak Current Limiting: Built-in current sense comparator monitors voltage drop across a small series resistor (Rsc), protecting the internal switch from inductor saturation and short circuits.
• Precision 1.25V Reference: On-chip bandgap reference provides tight line and load regulation over operating temperature extremes.
• Low Standby Quiescent Current: Low typical operating current of 2.5mA maximizes battery lifespan in portable and standby systems.

Common Applications

• Car USB Phone Chargers & Power Adapters: Stepping down 12V/24V vehicle battery power to regulated +5V USB supply rails.
• Negative Voltage Generation: Inverting +5V or +12V inputs into -5V or -12V rails for operational amplifiers, analog multiplexers, and LCD bias supplies.
• Step-Up Boost Converters: Boosting single/dual-cell battery voltages (3.7V Li-ion or 3V alkaline) to +5V, +9V, or +12V logic and sensor buses.
• Industrial Auxiliary Power Supplies: Point-of-load DC-DC step-down converters for microcontroller modules, relays, and LED displays.
• Nixie Tube & High-Voltage Micro-Supplies: External-transistor-assisted boost converters producing 170V–200V DC from 9V–12V supplies.

Usage Tips

• Output Voltage Setting Formula:
  • Step-Down / Step-Up: Vout = 1.25V × (1 + R2 / R1), where R1 is connected between Pin 5 (FB) and GND, and R2 is between Vout and Pin 5.
  • Inverting Mode: |Vout| = 1.25V × (1 + R2 / R1) - Vref (referencing the internal comparator to negative output ground).
• Current Sense Resistor (Rsc) Sizing: Calculate the current sense resistor placed between Pin 6 (Vcc) and Pin 7 using: Rsc = 0.3V / Ipk(switch). Use a non-inductive metal film or wirewound power resistor rated for the expected input current.
• Use Fast Schottky Catch Diodes: Always pair the MC34063A with a high-speed Schottky barrier rectifier (such as 1N5819 for ≤1A loads or 1N5822 / SS34 for up to 3A peak) rather than standard 1N4007 silicon rectifiers to ensure high conversion efficiency and prevent switch breakdown.
• Inductor Selection & Saturation: Choose a power inductor whose DC saturation current (Isat) is at least 20% to 30% higher than the peak switch current (Ipk) to avoid saturation and destructive current spikes through the internal switch.
• PCB Layout & Decoupling: Keep the high-current switching loop (Pin 1/2, inductor, catch diode, and output capacitor) as compact as possible. Place a 100nF low-ESR ceramic capacitor directly across Pin 6 (Vcc) and Pin 4 (GND) close to the IC to prevent switching ripple from disturbing the internal oscillator.

Datasheet