MPSA42 Reference Tables, Pins & Specifications

Pin reference

Signal names, electrical functions and connection guidance

TO-92

Physical pin numbers3 pins

Scroll within the table to see all columns and rows.

MPSA42 pin functions and connections
Signal	Type	Function & connection
E	Emitter	Emitter terminal of the bipolar transistor. Connection guidance Connect to common ground in the low-side example. TO-92 pin 1 becomes SOT-23 pin 2.
B	Base	Base current controls the collector current within the circuit operating region. Connection guidance Drive through 4.7 kΩ; connect 100 kΩ from base to emitter. TO-92 pin 2 becomes SOT-23 pin 1.
C	Collector	Load-current terminal of the transistor. Connection guidance Sinks current from the LED and its resistor. Collector remains physical pin 3 in both selected packages.

Reviewed Diotec selections

Manufacturer-referenced values4 parameters

Scroll within the table to see all columns and rows.

Parameter	Value	Conditions / notes
Through-hole selection	MPSA42BK	Straight-lead TO-92: E1, B2, C3
SMD selection	MMBTA42	SOT-23: B1, E2, C3
SMD marking	1D	Manufacturer marking code
Polarity	NPN	Magnitudes shown for PNP values

Physical pin numbers change between packages; connect by E/B/C function.

25°C unless stated

Manufacturer-referenced values6 parameters

Scroll within the table to see all columns and rows.

Parameter	Value	Conditions / notes
Collector-emitter / collector-base	300 / 300 V magnitudes	Base open / emitter open
Emitter-base reverse	6 V magnitude	Collector open
DC collector current	500 mA magnitude	Apply power and junction-temperature limits
Power dissipation	625 mW	Leads held at ambient temperature 2 mm from case
Junction temperature	−55 to +150°C	Absolute range
Junction-to-ambient	<200 K/W	Manufacturer lead-cooling condition

300 V and 500 mA are not a simultaneous operating point.

25°C · package-specific test points

Manufacturer-referenced values7 parameters

Scroll within the table to see all columns and rows.

Parameter	Value	Conditions / notes
Gain at 1 / 10 / 30 mA	>25 / >40 / >40	\|VCE\| = 10 V
Collector saturation voltage	<0.50 V	\|IC\| = 20 mA; \|IB\| = 2 mA
Base saturation voltage	<0.90 V	\|IC\| = 20 mA; \|IB\| = 2 mA
Collector-base leakage	<100 nA	\|VCB\| = 200 V; emitter open
Emitter-base leakage	<100 nA	\|VEB\| = 6 V; see manufacturer terminal-bias condition
Transition frequency	>50 MHz	\|VCE\| = 20 V; \|IC\| = 10 mA; f = 100 MHz
Collector-base capacitance	<3 pF	\|VCB\| = 20 V; 1 MHz

On-state values use pulsed measurements; typical frequency is not a guaranteed switching rate.

Independent manufacturer reference

Manufacturer-referenced values10 parameters

Scroll within the table to see all columns and rows.

Parameter	Value	Conditions / notes
VCEO / VCBO / VEBO	300 / 300 / 6 V magnitudes	Absolute limits with the specified third terminal open
DC collector current	500 mA magnitude	Apply thermal constraints
Power dissipation	250 mW	PCB with 3 mm² copper at each terminal
Gain at 10 mA	80–200	\|VCE\| = 10 V
Gain at 1 / 30 mA	>25 / >40	\|VCE\| = 10 V
VCE(sat) / VBE(sat)	<0.50 / <0.90 V	\|IC\| = 20 mA; \|IB\| = 2 mA
Transition frequency	>50 MHz	\|VCE\| = 20 V; \|IC\| = 10 mA; f = 100 MHz
Collector-base capacitance	<3 pF	\|VCB\| = 20 V; 1 MHz
Junction / storage	−55 to +150°C	Absolute ranges
Body / full lead span	2.9 × 1.3 / 2.4 mm nominal	Paired-contact pitch 1.9 mm

SMD values belong to the exact listed part; do not substitute the axial thermal rating.

Manufacturer straight-lead drawing

Manufacturer-referenced values6 parameters

Scroll within the table to see all columns and rows.

Parameter	Value	Conditions / notes
Body width / height	4.6 ±0.1 / 4.6 ±0.1 mm	Black flat-front molded body
Body depth	3.6 ±0.1 mm	Flat face 1.1 ±0.2 mm from lead plane
Lead pitch	1.27 ±0.1 mm	Straight-lead option
Lead width / thickness	0.4 +0.15/−0.05 / 0.34 ±0.05 mm	Silver plated stamped contacts
Supplied lead length	≥12.5 mm	Preview shows trimmed leads for readability
Authored pad / hole	1.10 × 1.55 / 0.80 mm	Engineering footprint; review fabrication tolerance

The 2.54 mm formed tape option is a different mounting geometry.

Teaching assumptions, not measured values

Manufacturer-referenced values7 parameters

Scroll within the table to see all columns and rows.

Parameter	Value	Conditions / notes
Load / base / bias resistors	470 Ω / 4.7 kΩ / 100 kΩ	Use separate current limits
Assumed drops	LED 2.0 V; \|VBE\| 0.7 V; \|VCE(sat)\| 0.2 V	Actual drops vary
Collector current	5.96 mA	(5 − 2 − 0.2) / 470
Net base current	0.908 mA	(5 − 0.7) / 4700 − 0.7 / 100000
Forced current ratio	Approximately 6.56	Collector / base current
Transistor dissipation	Approximately 1.83 mW	Collector-emitter plus base-emitter terms
Inductive loads	Require a revised circuit	Add suitable flyback protection; not pictured here

The example is a low-current LED switch; it does not demonstrate the maximum-current rating.