MMBTA70LT1 Equivalent & Substitute Parts

Part Overview

The MMBTA70LT1 is a PNP bipolar junction transistor manufactured by onsemi, rated for 40 V collector-emitter breakdown voltage and 100 mA maximum collector current. This device is packaged in SOT-23-3 (TO-236) surface mount configuration and is designed for general-purpose switching and amplification applications operating across a temperature range of -55°C to 150°C.

The MMBTA70LT1 is classified as obsolete. Substitute parts are necessary to maintain design continuity and ensure component availability for new production runs and field replacements. The substitute parts listed maintain electrical compatibility within the specified parameter ranges while offering active product status and improved availability.

Key Parameters

Parameter	Value	Unit
Transistor Type	PNP	—
Current - Collector (Ic) (Max)	100	mA
Voltage - Collector Emitter Breakdown (Max)	40	V
Power - Max	225	mW
Frequency - Transition	125	MHz
Operating Temperature Range	-55 to 150	°C
Mounting Type	Surface Mount	—
Package / Case	SOT-23-3 (TO-236)	—

Substitute Part Grouping Explanation

Substitution of the MMBTA70LT1 is determined by the following critical electrical and mechanical parameters:

Electrical Compatibility Criteria:

Transistor Type: PNP (required match)
Current - Collector (Ic) (Max): 100 mA (substitute must equal or exceed)
Voltage - Collector Emitter Breakdown (Max): Substitute must equal or exceed 40 V
Power - Max: Substitute must equal or exceed 225 mW
Frequency - Transition: Substitute must equal or exceed 125 MHz
Operating Temperature Range: Substitute must cover or exceed -55°C to 150°C

Mechanical Compatibility Criteria:

Mounting Type: Surface Mount (required match)
Package / Case: SOT-23-3 / TO-236 compatible packages (required match)

Substitute parts are grouped into two categories based on voltage rating:

Category A (40 V Rated): No substitute parts in the provided list meet the full 40 V breakdown voltage requirement while maintaining all other parameters.

Category B (30-32 V Rated): Parts with reduced voltage ratings (30 V or 32 V) that maintain 100 mA collector current, surface mount SOT-23-3 packaging, and operating temperature compatibility. These parts are suitable for applications where the circuit design operates below the reduced voltage threshold.

Parameter Comparison

Part Number	Manufacturer	Ic (Max) mA	Vce Breakdown (Max) V	Power (Max) mW	Frequency (MHz)	Temp Range °C	Package	Product Status
MMBTA70LT1	onsemi	100	40	225	125	-55 to 150	SOT-23-3	Obsolete
BC858A RFG	Taiwan Semiconductor Corporation	100	30	200	100	-55 to 150	SOT-23-3	Active
BC858B RFG	Taiwan Semiconductor Corporation	100	30	200	100	-55 to 150	SOT-23-3	Active
BC858B-HF	Comchip Technology	100	30	250	100	-65 to 150	SOT-23-3	Active
BC858CE6327HTSA1	Infineon Technologies	100	30	330	250	-55 to 150	SOT-23-3	Last Time Buy
BC859C,235	Nexperia USA Inc.	100	30	250	100	-55 to 150	SOT-23-3	Active
BCW29,235	Nexperia USA Inc.	100	32	250	100	-55 to 150	SOT-23-3	Active
BCW61B,215	Nexperia USA Inc.	100	32	250	100	-55 to 150	SOT-23-3	Active
BCW61DE6327HTSA1	Infineon Technologies	100	32	330	250	-55 to 150	SOT-23-3	Obsolete

Engineering Selection Recommendations

Primary Consideration: Voltage Rating Limitation

All substitute parts listed operate at reduced maximum collector-emitter breakdown voltages (30 V or 32 V) compared to the MMBTA70LT1 (40 V). Substitution is valid only for circuit designs where the actual operating voltage remains below the substitute part's rated breakdown voltage.

Active Status Substitutes (Recommended for New Designs):

BC858B RFG (Taiwan Semiconductor Corporation): Active product status with 30 V rating, 100 mA collector current, and SOT-23-3 packaging. Suitable for applications operating below 30 V.
BC858B-HF (Comchip Technology): Active product status with extended lower operating temperature (-65°C), 30 V rating, and increased power dissipation (250 mW). Suitable for low-temperature environments below 30 V operation.
BC859C,235 (Nexperia USA Inc.): Active product status with automotive qualification (AEC-Q101), 30 V rating, and 250 mW power rating. Suitable for automotive applications operating below 30 V.
BCW29,235 (Nexperia USA Inc.): Active product status with automotive qualification (AEC-Q101), 32 V rating (closest to original 40 V), and 250 mW power rating. Suitable for automotive applications operating below 32 V.
BCW61B,215 (Nexperia USA Inc.): Active product status with automotive qualification (AEC-Q101), 32 V rating, and 250 mW power rating. Suitable for automotive applications operating below 32 V.

Last Time Buy Status (Limited Availability):

BC858CE6327HTSA1 (Infineon Technologies): Last Time Buy status with 30 V rating, 250 MHz transition frequency (exceeds original 125 MHz), and 330 mW power dissipation. Suitable for high-frequency applications below 30 V with limited procurement window.
BCW61DE6327HTSA1 (Infineon Technologies): Obsolete status with 32 V rating and 250 MHz transition frequency. Not recommended for new designs due to obsolete classification.

RoHS and Compliance Status:

All substitute parts are RoHS3 compliant and REACH unaffected, meeting current environmental and regulatory requirements. The original MMBTA70LT1 is RoHS non-compliant.

Frequently Asked Questions (FAQ)

Q: Can the MMBTA70LT1 be directly replaced with any of the listed substitute parts?

A: Direct replacement is possible only if the circuit design operates at voltages below the substitute part's maximum collector-emitter breakdown voltage. The MMBTA70LT1 is rated for 40 V, while all substitutes are rated at 30 V or 32 V. Circuit analysis must confirm that actual operating voltages remain within the substitute part's specifications.

Q: What is the primary difference between the substitute parts?

A: The primary differences are voltage rating (30 V vs. 32 V), power dissipation capability (200 mW to 330 mW), transition frequency (100 MHz to 250 MHz), and product status (Active, Last Time Buy, or Obsolete). The 32 V rated parts (BCW29,235 and BCW61B,215) provide the closest voltage margin to the original 40 V specification.

Q: Are all substitute parts available in the same SOT-23-3 package?

A: Yes, all substitute parts are available in SOT-23-3 (TO-236) surface mount packaging, ensuring mechanical and pin compatibility with the original MMBTA70LT1 footprint.

Q: Which substitute part is recommended for automotive applications?

A: BC859C,235, BCW29,235, and BCW61B,215 are all qualified to AEC-Q101 automotive standards. BCW29,235 and BCW61B,215 offer the highest voltage rating at 32 V among automotive-qualified options.

Q: What is the difference between BC858B RFG and BC858B-HF?

A: Both are BC858B variants with 30 V ratings and 100 mA collector current. BC858B-HF offers extended lower operating temperature (-65°C vs. -55°C) and increased power dissipation (250 mW vs. 200 mW). BC858B-HF is suitable for applications requiring operation at temperatures below -55°C.

Q: Can I use a substitute part rated at 30 V in a 40 V circuit?

A: No. Using a 30 V rated part in a circuit designed for 40 V operation creates risk of device failure due to exceeding the maximum collector-emitter breakdown voltage. Circuit redesign or selection of a 32 V rated substitute (BCW29,235 or BCW61B,215) is required.

Q: What is the significance of the "Last Time Buy" status for BC858CE6327HTSA1?

A: Last Time Buy status indicates that the manufacturer has announced end-of-life for this part. While currently available, procurement should be completed before the manufacturer discontinues production. This part is not recommended for new long-term production designs.

Q: Are there any RoHS compliance differences between the MMBTA70LT1 and substitute parts?

A: Yes. The MMBTA70LT1 is RoHS non-compliant, while all substitute parts are RoHS3 compliant. For applications requiring RoHS compliance, any of the listed substitute parts satisfy current environmental regulations.

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