I need to find the SMD equivalent of a transistor - Page 1
Forum section: electronics / general

author: jackbauer
author_rank: Newbie
timestamp: April 26, 2023, 06:41:47 am
content: I'm having trouble finding an equivalent for either bc456, bc457 or bc458, which has the very same values or higher voltage and watts but keeping the other values as the same.Whether I find an "equivalent" SMD, it either has a lower frequency or wattage. Can anyone help me out?

author: mariush
author_rank: Super Contributor
timestamp: April 26, 2023, 07:52:24 am
content: BC 456Polarity: PNPMaximum Collector Power Dissipation: 0.3 WMaximum Collector-Base Voltage: 30 VMaximum Collector-Emitter Voltage: 30 VMaximum Emitter-Base Voltage: 5 VMaximum Collector Current: 0.1 AMaximum Operating Junction Temperature: 125 °CTransition Frequency: 150 MHzForward Current Transfer Ratio (hFE Value): 125Collector Capacitance: 6 pFPackage: TO92In bold you have the properties of the replacement, if they're different :2SA2029 :https://www.digikey.com/en/products/detail/onsemi/2SA2029M3T5G/1475407NS2029 :https://www.digikey.com/en/products/detail/onsemi/NS2029M3T5G/1792901Polarity: PNPMaximum Collector Power Dissipation: 0.30 W0.265WMaximum Collector-Base Voltage: 30 V60vMaximum Collector-Emitter Voltage: 30 V50vMaximum Emitter-Base Voltage: 5 V6vMaximum Collector Current: 0.1 AMaximum Operating Junction Temperature: 125 °C150cTransition Frequency: 150 MHz140 MhzForward Current Transfer Ratio (hFE Value): 125min. 120, max 560Collector Capacitance: 6 pF3.5pFPackage: TO92SOT-23They're general purpose pnp transistors, they're unlikely to be used at close to their maximum specifications.Maybe this would also work, just has lower collector emitter voltage.MMS8550 :https://www.digikey.com/en/products/detail/onsemi/2SA2029M3T5G/1475407Polarity: PNPMaximum Collector Power Dissipation: 0.30 W0.30WMaximum Collector-Base Voltage: 30 V40vMaximum Collector-Emitter Voltage: 30 V25vMaximum Emitter-Base Voltage: 5 V5vMaximum Collector Current: 0.1 A0.5AMaximum Operating Junction Temperature: 125 °C150cTransition Frequency: 150 MHzForward Current Transfer Ratio (hFE Value): 125min. 120, max 350Collector Capacitance: 6 pF?Package: TO92SOT-23higher voltage ...BC806 :https://www.digikey.com/en/products/detail/nexperia-usa-inc/BC806-16VL/10496455Polarity: PNPMaximum Collector Power Dissipation: 0.30 W0.25W - 0.345W if big enough padMaximum Collector-Base Voltage: 30 V80vMaximum Collector-Emitter Voltage: 30 V80vMaximum Emitter-Base Voltage: 5 V8vMaximum Collector Current: 0.1 A0.5AMaximum Operating Junction Temperature: 125 °C150cTransition Frequency: 150 MHzForward Current Transfer Ratio (hFE Value): 125min. 100, max 250 for -16 version, 160 - 400 for -25 versionCollector Capacitance: 6 pF5 pFPackage: TO92SOT-23

author: jackbauer
author_rank: Newbie
timestamp: April 26, 2023, 04:13:00 pm
content: The frequency of those is twice lower, are you sure they're fit for the job? Also, those are all PNP, I need NPN.

author: TimFox
author_rank: Super Contributor
timestamp: April 26, 2023, 04:18:33 pm
content: The BC456 and BC457 are PNP.The BC458 is NPN.

author: mariush
author_rank: Super Contributor
timestamp: April 26, 2023, 05:07:21 pm
content: Quote from: jackbauer on April 26, 2023, 04:13:00 pmWell, what frequency are you talking about, that is twice lower?Also, maybe you meant BC547 which is NPN transistor? For BC457 I couldn't even find a datasheet.

author: jackbauer
author_rank: Newbie
timestamp: April 26, 2023, 05:53:38 pm
content: omg, I'm so sorry, I made a terrible mistake. The transistors that I'm talking about are the BC546, BC547 and BC548. My eyes fooled me.................I'm terribly sorry for that.The frequency is 300mhz.

author: wraper
author_rank: Unknown
timestamp: April 26, 2023, 06:04:45 pm
content: General replacement for those isBC807EDIT: I meant BC817with appropriate gain suffix unless you need higher voltage rating of BC546. Also you can use MMBT3904.

author: Kleinstein
author_rank: Super Contributor
timestamp: April 26, 2023, 08:07:41 pm
content: The direct replacements should be the BC847 to BC849. With some letters added there can be a few smaller cases besides the normal SOT23. These are pretty much standard small signal transistors. The MMBT3904 are already a bit larger die, but still similar.The heat transfer with SMD parts depends a lot on the layout / copper area. With little copper the SOT23 may run hotter than TO92 - with lots of copper it may be OK.If heat is an issue I would consider a larger case like SOT223, but those transistrors tend to have more capacitance too.