BSS79C NPN Bipolar Transistor Equivalent & Substitute Parts

Part Overview

The BSS79C is an NPN bipolar junction transistor manufactured by onsemi, rated for 40V collector-emitter breakdown voltage and 800mA maximum collector current in a surface mount SOT-23-3 package. This device is classified as obsolete, necessitating identification of active equivalent and substitute components for new designs and production continuity. The BSS79C operates across a temperature range of -55°C to 150°C with a maximum power dissipation of 350mW and transition frequency of 250MHz.

Key Parameters

Parameter	Value	Unit
Transistor Type	NPN	—
Voltage - Collector Emitter Breakdown (Max)	40	V
Current - Collector (Ic) (Max)	800	mA
Vce Saturation (Max) @ Ib, Ic	1V @ 50mA, 500mA	—
DC Current Gain (hFE) (Min) @ Ic, Vce	100 @ 150mA, 10V	—
Power - Max	350	mW
Frequency - Transition	250	MHz
Operating Temperature Range	-55 to 150	°C
Package / Case	SOT-23-3 (TO-236-3, SC-59)	—
Mounting Type	Surface Mount	—
Product Status	Obsolete	—

Substitute Part Grouping Explanation

Substitute parts for the BSS79C are categorized based on electrical parameter compatibility within the SOT-23-3 surface mount package. The primary substitution criteria are:

Critical Parameters for Substitution:

Transistor type: NPN configuration
Package: SOT-23-3 (TO-236-3, SC-59) surface mount
Voltage rating: Collector-emitter breakdown voltage ≥ 40V
Current capability: Collector current (Ic) ≥ 800mA
Operating temperature range: -55°C to 150°C minimum
Mounting type: Surface mount

Substitution Categories:

Direct Substitute (Higher Current Capability): NSS40201LT1G provides identical 40V voltage rating with enhanced 2A collector current capability, making it suitable for applications requiring higher current handling while maintaining the same voltage specification.

Similar Substitutes (Voltage/Current Trade-offs): BC817-16LT1G, BC847BLT3G, BC847CLT1G, BCW65ALT1G, BCW65CLT1G, MMBT2222ALT3G, MMBT489LT1G, MMBT6429LT1G, and NSS30101LT1G offer alternative voltage and current ratings within the SOT-23-3 package. These parts maintain NPN configuration and surface mount compatibility but feature different electrical specifications suited to specific application requirements.

Parameter Comparison

Part Number	Manufacturer	Product Status	Ic (Max) mA	Vce Breakdown (Max) V	Power (Max) mW	Frequency (Transition) MHz	Package	RoHS Status
BSS79C	onsemi	Obsolete	800	40	350	250	SOT-23-3	—
NSS40201LT1G	onsemi	Active	2000	40	460	150	SOT-23-3	ROHS3 Compliant
BC817-16LT1G	onsemi	Active	500	45	300	100	SOT-23-3	ROHS3 Compliant
BC847BLT3G	onsemi	Active	100	45	300	100	SOT-23-3	ROHS3 Compliant
BC847CLT1G	onsemi	Active	100	45	300	100	SOT-23-3	ROHS3 Compliant
BCW65ALT1G	onsemi	Active	800	32	225	100	SOT-23-3	ROHS3 Compliant
BCW65CLT1G	onsemi	Active	800	32	225	100	SOT-23-3	ROHS3 Compliant
MMBT2222ALT3G	onsemi	Active	600	40	300	300	SOT-23-3	ROHS3 Compliant
MMBT489LT1G	onsemi	Active	1000	30	710	100	SOT-23-3	ROHS3 Compliant
MMBT6429LT1G	onsemi	Active	200	45	225	700	SOT-23-3	ROHS3 Compliant
NSS30101LT1G	onsemi	Active	1000	30	310	100	SOT-23-3	ROHS3 Compliant

Engineering Selection Recommendations

For Direct Replacement (Preferred):

NSS40201LT1G is the primary substitute for BSS79C. This part maintains the 40V collector-emitter breakdown voltage specification while providing enhanced 2A collector current capability. NSS40201LT1G is active in production status with ROHS3 compliance, ensuring long-term availability and regulatory alignment. The increased current rating provides design margin for applications operating near the BSS79C's 800mA limit.

For Current-Limited Applications:

MMBT2222ALT3G serves applications where collector current does not exceed 600mA. This part matches the 40V voltage rating and provides superior transition frequency (300MHz versus BSS79C's 250MHz). ROHS3 compliance and active production status ensure supply continuity.

For Lower Voltage Applications (≤32V):

BCW65ALT1G and BCW65CLT1G are suitable for designs operating at 32V or below. Both parts accommodate 800mA collector current, matching the BSS79C's current specification. BCW65CLT1G offers higher DC current gain (250 @ 100mA, 1V) compared to BCW65ALT1G (100 @ 100mA, 1V). Both are ROHS3 compliant and actively produced.

For Higher Current Applications (≥1A):

MMBT489LT1G and NSS30101LT1G both support 1A collector current. MMBT489LT1G operates at 30V maximum, while NSS30101LT1G also operates at 30V. NSS30101LT1G provides lower power dissipation (310mW versus 710mW), making it preferable for thermally constrained designs. Both are ROHS3 compliant and in active production.

For High-Frequency Applications:

MMBT6429LT1G features 700MHz transition frequency, significantly exceeding BSS79C's 250MHz specification. This part is suitable for RF and high-speed switching applications. The 45V voltage rating and 200mA current capability define its application scope. ROHS3 compliance and active status support modern design requirements.

All recommended substitutes are manufactured by onsemi, maintain SOT-23-3 surface mount packaging, and operate across the -55°C to 150°C temperature range. All substitute parts carry ROHS3 compliance certification.

Frequently Asked Questions (FAQ)

Q: Can NSS40201LT1G directly replace BSS79C in all applications?

A: NSS40201LT1G maintains identical 40V voltage rating and exceeds the 800mA current specification with 2A capability. The part is pin-compatible in SOT-23-3 packaging. However, the reduced transition frequency (150MHz versus 250MHz) may affect high-frequency switching performance. Applications operating below 150MHz transition frequency experience no functional impact.

Q: What is the primary difference between BC847BLT3G and BC847CLT1G?

A: Both parts are identical in electrical ratings (45V, 100mA, 100MHz, SOT-23-3 package). The distinction lies in DC current gain specification: BC847BLT3G provides minimum 200 hFE @ 2mA, 5V, while BC847CLT1G provides minimum 420 hFE @ 2mA, 5V. BC847CLT1G is preferred for applications requiring higher current gain.

Q: Are BCW65ALT1G and BCW65CLT1G interchangeable?

A: Both parts share identical electrical specifications (32V, 800mA, 100MHz, SOT-23-3 package) and operating temperature range. The difference is DC current gain: BCW65ALT1G provides 100 hFE @ 100mA, 1V, while BCW65CLT1G provides 250 hFE @ 100mA, 1V. Selection depends on circuit bias requirements.

Q: Why does MMBT489LT1G have higher power dissipation (710mW) than NSS30101LT1G (310mW) despite identical current and voltage ratings?

A: Power dissipation differences reflect variations in saturation voltage characteristics and internal device design. NSS30101LT1G exhibits lower saturation voltage, resulting in reduced power dissipation at equivalent operating conditions. For thermally constrained applications, NSS30101LT1G is preferred.

Q: Is MMBT6429LT1G suitable for replacing BSS79C in general-purpose switching circuits?

A: MMBT6429LT1G operates at 45V and 200mA maximum, below BSS79C's 800mA specification. This part is unsuitable for applications requiring 800mA collector current. However, for low-current switching circuits (≤200mA), MMBT6429LT1G's 700MHz transition frequency provides superior high-frequency performance.

Q: What packaging considerations apply to all substitute parts?

A: All substitute parts utilize SOT-23-3 (TO-236-3, SC-59) surface mount packaging, maintaining identical footprint and pin configuration with BSS79C. No PCB layout modifications are required for mechanical compatibility.

Q: Are all substitute parts ROHS3 compliant?

A: All active substitute parts listed carry ROHS3 compliance certification. BSS79C, being obsolete, does not carry RoHS certification. Designs transitioning from BSS79C to active substitutes achieve RoHS compliance through part selection.

Q: Which substitute part provides the closest electrical match to BSS79C?

A: NSS40201LT1G provides the closest match, maintaining 40V voltage rating and exceeding 800mA current specification. MMBT2222ALT3G also matches the 40V rating with 600mA current capability and superior 300MHz transition frequency. Selection between these parts depends on specific current and frequency requirements.

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