KST55MTF PNP Bipolar Junction Transistor Equivalent & Substitute Parts

Part Overview

The KST55MTF is a PNP bipolar junction transistor manufactured by onsemi, rated for 60V collector-emitter breakdown voltage and 500mA maximum collector current in a surface mount SOT-23-3 package. This device is classified as obsolete, making substitute parts necessary for new designs and ongoing production requirements. The KST55MTF serves in general-purpose switching and amplification applications requiring low-power PNP transistor functionality with moderate frequency response.

Key Parameters

Parameter	Value	Unit
Transistor Type	PNP	—
Collector Current (Max)	500	mA
Collector-Emitter Breakdown Voltage (Max)	60	V
Vce Saturation (Max) @ Ib, Ic	250mV @ 10mA, 100mA	—
Collector Cutoff Current (Max)	100	nA
DC Current Gain (hFE Min) @ Ic, Vce	50 @ 100mA, 1V	—
Power Dissipation (Max)	350	mW
Transition Frequency	50	MHz
Package Type	SOT-23-3 (TO-236-3, SC-59)	—
Mounting Type	Surface Mount	—
Product Status	Obsolete	—

Substitute Part Grouping Explanation

Substitute parts for the KST55MTF are grouped based on strict electrical and mechanical compatibility criteria. The primary substitution parameters are:

Critical Parameters (Must Match or Exceed):

Transistor Type: PNP
Collector-Emitter Breakdown Voltage: 60V minimum
Collector Current Rating: 500mA minimum
Package Type: SOT-23-3 compatible surface mount
Mounting Type: Surface Mount

Secondary Parameters (Functional Equivalence):

DC Current Gain (hFE): 50 minimum at specified conditions
Collector Cutoff Current: 100nA maximum
Power Dissipation: 350mW or greater

Substitute parts are classified into two categories:

Direct Substitutes (Electrical and Mechanical Equivalence): Parts meeting all critical parameters with identical or superior electrical characteristics and active product status.

Similar Substitutes (Functional Compatibility with Parameter Variations): Parts meeting core electrical requirements but with variations in secondary parameters such as power dissipation, transition frequency, or saturation voltage. These parts maintain functional compatibility within the KST55MTF application envelope.

Parameter Comparison

Part Number	Manufacturer	Ic (Max) mA	Vce(br) V	Vce Sat @ Ib,Ic	hFE (Min) @ Ic,Vce	Power mW	fT MHz	Package	Status
KST55MTF	onsemi	500	60	250mV @ 10mA, 100mA	50 @ 100mA, 1V	350	50	SOT-23-3	Obsolete
MMBTA55LT1G	onsemi	500	60	250mV @ 10mA, 100mA	100 @ 100mA, 1V	225	50	SOT-23-3	Active
MMBTA55-7-F	Diodes Incorporated	500	60	250mV @ 10mA, 100mA	100 @ 100mA, 1V	300	50	SOT-23-3	Active
BCX17T116	Rohm Semiconductor	500	45	620mV @ 50mA, 500mA	100 @ 100mA, 1V	425	200	SST3	Active
BSR16,215	Nexperia USA Inc.	600	60	1.6V @ 50mA, 500mA	100 @ 150mA, 10V	250	200	TO-236AB	Active
CMPT2907A BK PBFREE	Central Semiconductor Corp	600	60	1.6V @ 50mA, 500mA	100 @ 150mA, 10V	350	200	SOT-23	Active
CMPT2907A TR PBFREE	Central Semiconductor Corp	600	60	1.6V @ 50mA, 500mA	100 @ 150mA, 10V	350	200	SOT-23	Active
CMPT2907AE TR PBFREE	Central Semiconductor Corp	600	60	700mV @ 50mA, 500mA	100 @ 150mA, 10V	350	200	SOT-23	Active
PMBT2907A,215	NXP Semiconductors	600	60	1.6V @ 50mA, 500mA	100 @ 150mA, 10V	250	200	TO-236AB	Active
PMBT2907A,235	Nexperia USA Inc.	600	60	1.6V @ 50mA, 500mA	100 @ 150mA, 10V	250	200	TO-236AB	Active

Engineering Selection Recommendations

Direct Substitution (Preferred for Pin-Compatible Replacement):

MMBTA55LT1G and MMBTA55-7-F are the primary direct substitutes for KST55MTF. Both parts maintain identical electrical specifications for collector current, breakdown voltage, and saturation voltage at the specified test conditions. Both are active products with ROHS3 compliance and unlimited moisture sensitivity rating. MMBTA55LT1G is manufactured by onsemi (original KST55MTF manufacturer) and offers the closest design continuity. MMBTA55-7-F from Diodes Incorporated provides an alternative with AEC-Q101 automotive qualification.

Functional Substitutes (For Applications Tolerant of Parameter Variations):

CMPT2907A variants (BK PBFREE, TR PBFREE, AE TR PBFREE) from Central Semiconductor Corp support higher collector current (600mA) and maintain 60V breakdown voltage. These parts feature 200MHz transition frequency compared to the KST55MTF's 50MHz, enabling use in higher-frequency applications. All variants are active products with ROHS3 compliance.

PMBT2907A,215 and PMBT2907A,235 from NXP/Nexperia provide automotive-grade alternatives with AEC-Q101 qualification, 600mA collector current, and 200MHz transition frequency. Both maintain 60V breakdown voltage and are suitable for automotive applications requiring higher reliability qualification.

BSR16,215 from Nexperia offers 600mA collector current, 60V breakdown voltage, and AEC-Q101 automotive qualification. This part is suitable for applications requiring automotive-grade components with enhanced current handling.

Limited Compatibility Substitute:

BCX17T116 from Rohm Semiconductor has reduced collector-emitter breakdown voltage (45V versus 60V) and higher saturation voltage (620mV versus 250mV). This part is suitable only for applications where the 45V rating is acceptable and where higher saturation voltage does not compromise circuit performance. The 200MHz transition frequency supports higher-frequency operation.

Frequently Asked Questions (FAQ)

Q: Can MMBTA55LT1G directly replace KST55MTF without circuit modification?

A: Yes. MMBTA55LT1G maintains identical electrical specifications for collector current (500mA), breakdown voltage (60V), and saturation voltage (250mV @ 10mA, 100mA). Both use SOT-23-3 packaging. The primary difference is higher DC current gain (100 versus 50), which improves circuit performance without requiring design changes.

Q: What is the key difference between CMPT2907A variants and the KST55MTF?

A: CMPT2907A variants support higher collector current (600mA versus 500mA) and higher transition frequency (200MHz versus 50MHz). Saturation voltage is higher (1.6V @ 50mA, 500mA versus 250mV @ 10mA, 100mA). These parts are suitable for applications requiring higher current capacity or faster switching, provided the higher saturation voltage is acceptable.

Q: Is BCX17T116 suitable as a direct replacement?

A: BCX17T116 is not a direct replacement due to reduced collector-emitter breakdown voltage (45V versus 60V). Use this part only in applications where 45V rating is sufficient and where the higher saturation voltage (620mV) does not degrade circuit performance.

Q: What packaging considerations apply to these substitutes?

A: KST55MTF uses SOT-23-3 packaging. MMBTA55LT1G and MMBTA55-7-F maintain identical SOT-23-3 packaging for direct PCB compatibility. CMPT2907A variants use SOT-23 packaging (compatible footprint). PMBT2907A and BSR16 use TO-236AB packaging (compatible with SOT-23-3 pinout). BCX17T116 uses SST3 packaging (compatible pinout). Verify PCB footprint compatibility before selection.

Q: Which substitute offers the best long-term availability?

A: MMBTA55LT1G from onsemi (original manufacturer) and CMPT2907A variants from Central Semiconductor Corp show highest inventory levels (125,400 and 25,420+ units respectively). Both are active products with established supply chains.

Q: Are automotive-qualified alternatives available?

A: Yes. MMBTA55-7-F (Diodes Incorporated), PMBT2907A,215 and PMBT2907A,235 (NXP/Nexperia), and BSR16,215 (Nexperia) all carry AEC-Q101 automotive qualification. These parts are suitable for automotive applications requiring enhanced reliability certification.

Q: What is the impact of higher transition frequency in substitute parts?

A: CMPT2907A, PMBT2907A, and BSR16 variants feature 200MHz transition frequency versus KST55MTF's 50MHz. Higher transition frequency enables faster switching operation and supports higher-frequency signal processing. This enhancement does not negatively impact lower-frequency applications.

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