PDTC124XK,115 Pre-Biased NPN Bipolar Transistor Equivalent & Substitute Parts

Part Overview

The PDTC124XK,115 is a pre-biased NPN bipolar transistor (BJT) manufactured by NXP USA Inc., designed for surface mount applications in the SOT-23-3 (SMT3) package. This component integrates internal base and emitter resistors, enabling direct logic-level switching without external biasing networks. The device is rated for 50 V collector-emitter breakdown voltage and 100 mA maximum collector current with 250 mW power dissipation.

The PDTC124XK,115 is classified as obsolete. Identifying equivalent and substitute parts is necessary to maintain design continuity, ensure supply chain availability, and support ongoing production requirements for legacy systems or redesign initiatives.

Key Parameters

Parameter	Value	Unit
Transistor Type	NPN - Pre-Biased	—
Current - Collector (Ic) Max	100	mA
Voltage - Collector Emitter Breakdown (Max)	50	V
Resistor - Base (R1)	22	kOhms
Resistor - Emitter Base (R2)	47	kOhms
DC Current Gain (hFE) Min @ Ic, Vce	80 @ 5mA, 5V	—
Vce Saturation (Max) @ Ib, Ic	150	mV @ 500µA, 10mA
Current - Collector Cutoff (Max)	1	µA
Power - Max	250	mW
Package / Case	TO-236-3, SC-59, SOT-23-3	—
Mounting Type	Surface Mount	—
RoHS Status	ROHS3 Compliant	—
Moisture Sensitivity Level (MSL)	1 (Unlimited)	—

Substitute Part Grouping Explanation

Substitution of the PDTC124XK,115 is determined by the following critical parameters:

Electrical Compatibility Requirements:

Transistor type must be NPN pre-biased
Collector-emitter breakdown voltage must be ≥ 50 V
Maximum collector current must be ≥ 100 mA
Base resistor (R1) value: 22 kOhms (primary matching criterion)
Emitter-base resistor (R2) value: 47 kOhms (primary matching criterion)
DC current gain (hFE) and saturation voltage must support equivalent switching performance
Power dissipation rating must be ≥ 250 mW

Mechanical & Environmental Compatibility:

Package must be surface mount SOT-23-3 or equivalent footprint (TO-236-3, SC-59)
RoHS3 compliance required
MSL rating of 1 (Unlimited) preferred for supply chain flexibility

Substitutes are grouped into two categories:

Direct Electrical Equivalents – Parts with identical R1 (22 kOhms) and R2 (47 kOhms) resistor values, matching the PDTC124XK,115 biasing network
Functional Alternatives – Parts with different internal resistor configurations that may require circuit evaluation but maintain core electrical ratings

Parameter Comparison

Part Number	Manufacturer	Product Status	Ic Max (mA)	Vce Breakdown (V)	R1 (kOhms)	R2 (kOhms)	hFE Min @ Ic, Vce	Vce Sat Max (mV)	Power Max (mW)	Package
PDTC124XK,115	NXP USA Inc.	Obsolete	100	50	22	47	80 @ 5mA, 5V	150 @ 500µA, 10mA	250	SOT-23-3
DDTC124GCA-7-F	Diodes Incorporated	Active	100	50	—	22	56 @ 5mA, 5V	300 @ 500µA, 10mA	200	SOT-23-3
DDTC124GUA-7-F	Diodes Incorporated	Active	100	50	—	22	56 @ 5mA, 5V	300 @ 500µA, 10mA	200	SOT-323
DDTC124TCA-7-F	Diodes Incorporated	Active	100	50	22	—	100 @ 1mA, 5V	300 @ 500µA, 5mA	200	SOT-23-3
DDTC124TE-7-F	Diodes Incorporated	Active	100	50	22	—	100 @ 1mA, 5V	300 @ 500µA, 5mA	150	SOT-523
DDTC124TUA-7-F	Diodes Incorporated	Active	100	50	22	—	100 @ 1mA, 5V	300 @ 500µA, 5mA	200	SOT-323
DDTC124XCA-7-F	Diodes Incorporated	Active	100	50	22	47	68 @ 5mA, 5V	300 @ 500µA, 10mA	200	SOT-23-3
DTC124XCAT116	Rohm Semiconductor	Active	100	50	22	47	68 @ 5mA, 5V	300 @ 500µA, 10mA	200	SOT-23-3
DTC124XKAT146	Rohm Semiconductor	Active	50	50	22	47	68 @ 5mA, 5V	300 @ 500µA, 10mA	200	SOT-23-3
DTC143XKAT146	Rohm Semiconductor	Active	100	50	4.7	10	30 @ 10mA, 5V	300 @ 500µA, 10mA	200	SOT-23-3
MMUN2212LT1G	onsemi	Active	100	50	22	22	60 @ 5mA, 10V	250 @ 300µA, 10mA	246	SOT-23-3

Engineering Selection Recommendations

Primary Substitute (Direct Electrical Equivalent):

DDTC124XCA-7-F (Diodes Incorporated) is the recommended primary substitute for the PDTC124XK,115. This part maintains identical internal resistor configuration (R1 = 22 kOhms, R2 = 47 kOhms), matching electrical biasing characteristics. The device is in active production status, RoHS3 compliant, and available in high inventory (9,400 pcs). The SOT-23-3 package is mechanically and electrically compatible. Vce saturation is slightly elevated (300 mV vs. 150 mV), but remains within acceptable switching performance margins for pre-biased BJT applications.

Alternative Substitute (Same Package, Different Resistor Configuration):

DDTC124TCA-7-F (Diodes Incorporated) provides an alternative with R1 = 22 kOhms but undocumented R2 value. This part offers higher DC current gain (hFE = 100 @ 1mA, 5V vs. 80 @ 5mA, 5V), resulting in faster switching response. Active production status and high inventory (32,529 pcs) ensure supply continuity. SOT-23-3 package compatibility is confirmed. Circuit evaluation is required to validate performance in applications sensitive to biasing network differences.

Secondary Substitute (Compact Package Alternative):

DDTC124TUA-7-F (Diodes Incorporated) offers SOT-323 (SC-70) package for space-constrained designs. Electrical ratings match DDTC124TCA-7-F. Active production status and adequate inventory (9,300 pcs) support availability. PCB layout redesign is required due to package footprint change.

Rohm Semiconductor Options:

DTC124XCAT116 provides identical R1/R2 configuration (22 kOhms / 47 kOhms) in SST3 package variant. Active production with 2,997 pcs inventory. Electrical performance mirrors DDTC124XCA-7-F. Supplier device package designation (SST3) is mechanically equivalent to SOT-23-3.

DTC124XKAT146 maintains R1/R2 matching but reduces maximum collector current to 50 mA. This part is suitable only for applications where 100 mA rating is not required. High inventory (15,348 pcs) available.

onsemi Option:

MMUN2212LT1G provides R1 = 22 kOhms with R2 = 22 kOhms (different from original 47 kOhms). Power rating is 246 mW, closely matching the 250 mW specification. Vce saturation is 250 mV @ 300µA, 10mA. This part requires circuit validation due to altered biasing network.

Not Recommended:

DTC143XKAT146 has significantly different internal resistor values (R1 = 4.7 kOhms, R2 = 10 kOhms) and lower DC current gain (hFE = 30 @ 10mA, 5V). This part is functionally distinct and not suitable as a direct substitute.

Frequently Asked Questions (FAQ)

Q1: Can I use DDTC124XCA-7-F as a direct replacement for PDTC124XK,115 without circuit modification?

A: Yes. DDTC124XCA-7-F maintains identical internal resistor configuration (R1 = 22 kOhms, R2 = 47 kOhms), ensuring equivalent biasing behavior. Both devices are NPN pre-biased transistors rated for 50 V / 100 mA in SOT-23-3 packages. The primary difference is Vce saturation (300 mV vs. 150 mV), which is acceptable for most switching applications. No circuit modification is required.

Q2: What is the significance of the internal resistor values (R1 and R2)?

A: R1 (base resistor) and R2 (emitter-base resistor) form the internal biasing network of pre-biased transistors. These resistors determine the base current and switching threshold without external components. Matching R1 and R2 values ensures identical turn-on voltage and switching speed. Deviations in these values alter the transistor's response to input signals and may require circuit re-evaluation.

Q3: Why does DDTC124TCA-7-F have higher DC current gain (hFE = 100) compared to the original part (hFE = 80)?

A: DC current gain variation is inherent to transistor manufacturing and is specified at different test conditions. DDTC124TCA-7-F is tested at 1 mA collector current and 5 V Vce, while PDTC124XK,115 is tested at 5 mA and 5 V. Higher gain at lower collector current is typical for BJT devices. This difference may result in faster switching response but requires validation in the target application.

Q4: Can I substitute PDTC124XK,115 with a part in SOT-323 package (DDTC124TUA-7-F)?

A: Electrically, yes. DDTC124TUA-7-F provides equivalent electrical performance. However, SOT-323 (SC-70) has a different physical footprint than SOT-23-3 (TO-236-3). PCB layout and assembly tooling must be redesigned. This substitution is suitable only when board redesign is feasible.

Q5: What does "Product Status: Obsolete" mean for PDTC124XK,115?

A: Obsolete status indicates the part is no longer manufactured by NXP USA Inc. and is not available from primary sources. Existing inventory may be available from authorized distributors or secondary market sources, but long-term supply is not guaranteed. Identifying active production substitutes is essential for design continuity and future production planning.

Q6: Are all substitute parts RoHS3 compliant?

A: Yes. All substitute parts listed (DDTC124 series from Diodes Incorporated, DTC124 series from Rohm Semiconductor, and MMUN2212LT1G from onsemi) are RoHS3 compliant. Moisture Sensitivity Level (MSL) is 1 (Unlimited) for all parts, ensuring compatibility with standard storage and handling procedures.

Q7: Why is MMUN2212LT1G listed as a substitute if R2 differs (22 kOhms vs. 47 kOhms)?

A: MMUN2212LT1G is listed as a functional alternative, not a direct equivalent. The different R2 value (22 kOhms instead of 47 kOhms) alters the biasing network and switching characteristics. This part is suitable only if circuit simulation or bench testing confirms acceptable performance in the target application. Direct substitution without validation is not recommended.

Q8: What is the difference between DDTC124GCA-7-F and DDTC124XCA-7-F?

A: DDTC124GCA-7-F has R2 = 22 kOhms (R1 not specified), while DDTC124XCA-7-F has R1 = 22 kOhms and R2 = 47 kOhms. DDTC124XCA-7-F matches the original PDTC124XK,115 resistor configuration more closely. DDTC124GCA-7-F is a functional alternative with different biasing characteristics.

Q9: Is power dissipation rating critical for substitution?

A: Power rating should be ≥ 250 mW to ensure thermal margin. Most active substitutes are rated 200 mW or higher. In applications where the transistor operates near maximum power dissipation, verify that the substitute's thermal characteristics are adequate. MMUN2212LT1G (246 mW) and DDTC124TE-7-F (150 mW) have lower ratings and require application-specific evaluation.

Q10: Can I use DTC143XKAT146 as a substitute?

A: No. DTC143XKAT146 has significantly different internal resistor values (R1 = 4.7 kOhms, R2 = 10 kOhms) and lower DC current gain (hFE = 30 @ 10mA, 5V). This part is functionally distinct and will not provide equivalent switching performance. It is listed in the substitute database but is not recommended for direct replacement of PDTC124XK,115.

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