KA3843B Equivalent & Substitute Parts

Part Overview

The KA3843B is an offline switch IC manufactured by onsemi, designed for power management applications with converter offline topology operating up to 500kHz. The device is packaged in 8-DIP (0.300", 7.62mm) through-hole configuration. Currently, the KA3843B holds obsolete product status, making identification of functionally equivalent alternatives essential for ongoing design support, production continuity, and component sourcing in legacy system maintenance and new designs requiring compatible control topologies.

Key Parameters

Parameter	KA3843B Value
Manufacturer	onsemi
Package / Case	8-DIP (0.300", 7.62mm)
Mounting Type	Through Hole
Voltage - Supply (Vcc/Vdd)	12V ~ 25V
Frequency - Switching	Up to 500kHz
Duty Cycle	97%
Control Features	Frequency Control
Operating Temperature	0°C ~ 70°C (TA)
Voltage - Start Up	8.4 V
Product Status	Obsolete

Substitute Part Grouping Explanation

Substitution eligibility for the KA3843B is determined by the following critical parameters:

Package compatibility: 8-DIP (0.300", 7.62mm) through-hole mounting
Supply voltage range overlap: Minimum 12V operation capability
Switching frequency capability: Up to 500kHz operation
Duty cycle performance: Minimum 96% or higher
Control architecture: Frequency control feature
Operating temperature range: 0°C ~ 70°C minimum coverage
Pin-compatible topology support for offline converter applications

Substitute parts are classified into two categories:

Direct Substitutes meet all critical electrical and mechanical parameters within the specified ranges, enabling drop-in replacement without circuit modification.

Similar Parts share the same package, switching frequency, and control features but may have different supply voltage ranges, duty cycle specifications, or topology capabilities. These require circuit evaluation before implementation.

Parameter Comparison

Parameter	KA3843B	UC3843BNG	TL3843BP	LT1246CN8#PBF	TL3843P	UC2845BN	UC3843AN	UC3843BN	UC3843N
Manufacturer	onsemi	onsemi	Texas Instruments	Analog Devices Inc.	Texas Instruments	STMicroelectronics	onsemi	STMicroelectronics	Fairchild Semiconductor
Package / Case	8-DIP (0.300", 7.62mm)	8-DIP (0.300", 7.62mm)	8-DIP (0.300", 7.62mm)	8-DIP (0.300", 7.62mm)	8-DIP (0.300", 7.62mm)	8-DIP (0.300", 7.62mm)	8-DIP (0.300", 7.62mm)	8-DIP (0.300", 7.62mm)	8-DIP (0.300", 7.62mm)
Mounting Type	Through Hole	Through Hole	Through Hole	Through Hole	Through Hole	Through Hole	Through Hole	Through Hole	Through Hole
Voltage - Supply (Vcc/Vdd)	12V ~ 25V	7.6V ~ 30V	7.6V ~ 30V	10V ~ 25V	7.6V ~ 30V	7.6V ~ 30V	8.4V ~ 30V	7.6V ~ 30V	7.6V ~ 30V
Frequency - Switching	Up to 500kHz	Up to 500kHz	Up to 500kHz	Up to 1MHz	Up to 500kHz	Up to 500kHz	Up to 500kHz	Up to 500kHz	Up to 500kHz
Duty Cycle (Max)	97%	96%	96%	100%	97%	48%	96%	96%	97%
Control Features	Frequency Control	Frequency Control	Frequency Control	Frequency Control	Frequency Control	Frequency Control	Frequency Control	Frequency Control	Frequency Control
Operating Temperature	0°C ~ 70°C (TA)	0°C ~ 70°C (TA)	0°C ~ 70°C (TA)	0°C ~ 100°C (TA)	0°C ~ 70°C (TA)	-40°C ~ 150°C (TJ)	0°C ~ 70°C (TA)	0°C ~ 70°C (TJ)	0°C ~ 70°C (TA)
Product Status	Obsolete	Active	Active	Active	Active	Active	Obsolete	Active	Obsolete
RoHS Status	Not specified	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	RoHS non-compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

Direct Substitutes (Active Status, Full Parameter Compatibility):

UC3843BNG (onsemi) and TL3843BP (Texas Instruments) are the primary direct substitutes. Both devices operate within the KA3843B supply voltage range, support 500kHz switching frequency, achieve 96% duty cycle, and maintain identical 8-DIP through-hole packaging. Both are ROHS3 compliant and currently in active production status, ensuring long-term availability and supply chain stability.

TL3843P (Texas Instruments) provides equivalent functionality with 97% maximum duty cycle matching the original specification. This device is ROHS3 compliant and actively produced, offering an alternative from a different manufacturer with established design support.

Similar Parts (Topology or Parameter Variations):

UC2845BN (STMicroelectronics) shares identical package, switching frequency, and control architecture but specifies 48% maximum duty cycle, significantly lower than the KA3843B 97% specification. This limitation restricts applicability to specific converter topologies and requires circuit-level evaluation.

LT1246CN8#PBF (Analog Devices Inc.) operates at higher switching frequency (up to 1MHz) and supports 100% duty cycle, providing enhanced performance characteristics. However, the topology classification as Buck converter differs from the original offline switch designation, requiring topology compatibility verification.

UC3843AN (onsemi) and UC3843N (Fairchild Semiconductor) are obsolete products, limiting their suitability for new designs despite parameter compatibility. These are appropriate only for legacy system maintenance where existing inventory exists.

UC3843BN (STMicroelectronics) is an active product offering full parameter compatibility with ROHS3 compliance and extended operating temperature range capability.

Compliance Considerations:

For applications requiring RoHS compliance, UC3843AN must be excluded. All active-status substitutes (UC3843BNG, TL3843BP, TL3843P, UC2845BN, LT1246CN8#PBF, UC3843BN) meet ROHS3 requirements.

Frequently Asked Questions (FAQ)

Q: Can UC2845BN replace KA3843B in all applications?

A: UC2845BN shares the same 8-DIP package and 500kHz switching capability but specifies a maximum duty cycle of 48%, compared to KA3843B's 97%. This significant difference restricts its use to specific converter topologies. Circuit evaluation is required to determine compatibility with your application's duty cycle requirements.

Q: What is the primary difference between direct substitutes and similar parts?

A: Direct substitutes (UC3843BNG, TL3843BP, TL3843P) meet all electrical parameters within the KA3843B specification range and enable drop-in replacement. Similar parts (UC2845BN, LT1246CN8#PBF) share the package and switching frequency but have different duty cycle, supply voltage, or topology specifications, requiring circuit-level compatibility assessment.

Q: Are obsolete parts suitable for new designs?

A: Obsolete parts (UC3843AN, UC3843N) should not be selected for new designs due to uncertain long-term availability and potential supply discontinuation. These are appropriate only for maintaining existing legacy systems where component inventory is already established.

Q: Does package compatibility guarantee electrical compatibility?

A: No. While all listed parts share the 8-DIP through-hole package, electrical parameters such as supply voltage range, duty cycle, switching frequency, and control features must be verified against your circuit requirements. Package compatibility is a necessary but not sufficient condition for substitution.

Q: Which substitute offers the best compliance and availability?

A: UC3843BNG (onsemi) and TL3843BP (Texas Instruments) are both ROHS3 compliant, actively produced, and fully compatible with KA3843B electrical specifications. Both offer established supply chain availability and design support resources.

Q: Can LT1246CN8#PBF be used as a direct replacement?

A: LT1246CN8#PBF operates at higher switching frequency (1MHz vs. 500kHz) and supports 100% duty cycle. While it shares the 8-DIP package, its Buck topology classification differs from the original offline switch designation. Application-specific circuit evaluation is required before implementation.

Q: What temperature range considerations apply to substitute selection?

A: KA3843B operates 0°C ~ 70°C. Most substitutes maintain this range. UC2845BN extends to -40°C ~ 150°C, and LT1246CN8#PBF extends to 0°C ~ 100°C. Extended temperature capability may be beneficial for harsh environment applications but is not required for standard industrial use cases.

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