I need to find the SMD equivalent of a transistor

[jackbauer]

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?

[mariush]

BC 456

Polarity: PNP   
Maximum Collector Power Dissipation:  0.3 W
Maximum Collector-Base Voltage: 30 V
Maximum Collector-Emitter Voltage: 30 V
Maximum Emitter-Base Voltage: 5 V
Maximum Collector Current: 0.1 A
Maximum Operating Junction Temperature: 125 °C
Transition Frequency: 150 MHz
Forward Current Transfer Ratio (hFE Value): 125
Collector Capacitance: 6 pF
Package: TO92

In bold you have the properties of the replacement, if they're different :

2SA2029  :  https://www.digikey.com/en/products/detail/onsemi/2SA2029M3T5G/1475407
NS2029 : https://www.digikey.com/en/products/detail/onsemi/NS2029M3T5G/1792901

Polarity: PNP   
Maximum Collector Power Dissipation:  0.30 W   0.265W
Maximum Collector-Base Voltage: 30 V  60v
Maximum Collector-Emitter Voltage: 30 V  50v
Maximum Emitter-Base Voltage: 5 V  6v
Maximum Collector Current: 0.1 A
Maximum Operating Junction Temperature: 125 °C  150c
Transition Frequency: 150 MHz           140 Mhz
Forward Current Transfer Ratio (hFE Value): 125    min. 120, max 560
Collector Capacitance: 6 pF            3.5pF
Package: TO92   SOT-23

They'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/1475407

Polarity: PNP   
Maximum Collector Power Dissipation:  0.30 W   0.30W
Maximum Collector-Base Voltage: 30 V  40v
Maximum Collector-Emitter Voltage: 30 V  25v
Maximum Emitter-Base Voltage: 5 V  5v
Maximum Collector Current: 0.1 A   0.5A
Maximum Operating Junction Temperature: 125 °C  150c
Transition Frequency: 150 MHz         
Forward Current Transfer Ratio (hFE Value): 125    min. 120, max 350
Collector Capacitance: 6 pF            ?
Package: TO92   SOT-23


higher voltage ...

BC806 : https://www.digikey.com/en/products/detail/nexperia-usa-inc/BC806-16VL/10496455


Polarity: PNP   
Maximum Collector Power Dissipation:  0.30 W   0.25W - 0.345W if big enough pad
Maximum Collector-Base Voltage: 30 V  80v
Maximum Collector-Emitter Voltage: 30 V  80v
Maximum Emitter-Base Voltage: 5 V  8v
Maximum Collector Current: 0.1 A   0.5A
Maximum Operating Junction Temperature: 125 °C  150c
Transition Frequency: 150 MHz         
Forward Current Transfer Ratio (hFE Value): 125    min. 100, max 250 for -16 version, 160 - 400 for -25 version
Collector Capacitance: 6 pF            5 pF
Package: TO92   SOT-23

[jackbauer]

The frequency of those is twice lower, are you sure they're fit for the job? Also, those are all PNP, I need NPN.

[TimFox]

The BC456 and BC457 are PNP.
The BC458 is NPN.

[mariush]

The frequency of those is twice lower, are you sure they're fit for the job? Also, those are all PNP, I need NPN.

Well, 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.

[jackbauer]

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.

[wraper]

General replacement for those is BC807 EDIT: I meant BC817 with appropriate gain suffix unless you need higher voltage rating of BC546. Also you can use MMBT3904.

[Kleinstein]

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.