Explore MC34063A pins, signal names, electrical functions and connection guidance for each package.
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Collector of the internal high-current NPN switch.
In the buck example, connect to the current-sense resistor output and driver collector pin 8.
The 1.5 A rating is a peak switch limit, not a guaranteed load current.
Emitter of the internal output switch.
In the buck circuit, connect to L1 and the catch-diode cathode.
This is a switching node, not the filtered DC output.
An external capacitor sets the oscillator timing.
Connect the 470 pF example capacitor from CT to GND.
The 33 kHz typical specification is measured with CT = 1 nF; do not assign it to every timing capacitor.
Return for the reference, oscillator and comparator.
Join the input/output capacitor returns and diode anode with short power paths.
Keep the feedback return away from large switching currents.
Compares the output-divider voltage with the internal 1.25 V reference.
Connect to the junction of R2 from output and R1 to ground.
Output setting is approximately 1.25 × (1 + R2/R1).
Supplies the control circuitry.
Connect to VIN before the current-sense resistor and bypass locally.
Recommended supply range 3–40 V; the example uses 25 V.
Senses the drop between the supply and the current-sense node.
Connect after RSC, at the switch/driver collector feed.
Approximately 300 mV across RSC invokes current limiting; 250–350 mV at 25°C.
Collector supply of the internal driver transistor.
Join to pin 1 after RSC in this Darlington buck configuration.
Alternative driver configurations need the manufacturer’s base-drive design checks.
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