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TO-92 · S8550
ActivePNP Medium-Power BJT
S8550
Diodes Incorporated · TO-92 · PNP Medium-Power BJT
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Overview
The S8550 (Diodes Incorporated SS8550, also made by onsemi and many Asian vendors) is the PNP complement of the S8050 and the standard medium-power PNP transistor for Class-B push-pull output stages, high-side switching and complementary drivers. It is rated -25V collector-emitter, -40V collector-base and -6V emitter-base, with -1.5A continuous collector current and 1W dissipation at TA = 25°C (derate 8mW/°C, RθJA 125°C/W).
DC current gain is 85 to 300 at VCE = -1V and IC = -100mA (typical 160), with a guaranteed minimum of 40 at -800mA, and vendors bin the part into C (120-200) and D (160-300) gain bands. Saturation voltage is -0.5V maximum at IC = -800mA with IB = -80mA, and the gain-bandwidth product is 100MHz typical at VCE = -10V and IC = -50mA, matching the S8050 closely enough for symmetric audio stages.
As with its NPN partner, the S8550 is heavily second-sourced and heavily counterfeited; gain band, breakdown voltage and saturation differ noticeably between genuine Diodes/onsemi stock and no-name bags. For production specify the vendor code and band (for example SS8550DTA) and verify hFE at -100mA plus VCE(sat) at -800mA/-80mA on incoming inspection. Pinout is emitter-base-collector. Shenzhen stock is extremely deep, MOQ 2,000 pcs fan-fold or 10,000 pcs bulk box.
Key Features
- -25V / -1.5A PNP medium-power transistor in TO-92
- hFE 85-300 at IC = -100mA, binned C/D
- 1W dissipation at TA = 25°C
- VCE(sat) -0.5V max at -800mA
- Exact complement of S8050 for push-pull stages
Typical Applications
- Class-B push-pull audio output stages (with S8050)
- High-side switching of ground-referenced loads
- Complementary driver and level-shift stages
- Voltage regulators and constant-current sinks
- Portable radio and toy audio amplifiers
- H-bridge P-side helper switches
Specifications
- Polarity / Channel Type
- PNP
- Collector-Emitter Voltage (VCEO)
- -25 V
- Collector-Base Voltage (VCBO)
- -40 V
- Continuous Collector Current (IC)
- -1.5 A
- DC Current Gain hFE (VCE = -1 V, IC = -100 mA)
- 85 to 300
- VCE(sat) max (IC = -800 mA, IB = -80 mA)
- -0.5 V
- Gain-Bandwidth Product (fT)
- 100 MHz
- Power Dissipation (PD, TA = 25 °C)
- 1 W
- Pins
- 3
- RoHS
- Compliant
Procurement Tips
Buy S8050 and S8550 together from one vendor and one gain band per lot, and require hFE and VCE(sat) sample data; mismatched complementary pairs are the leading cause of crossover distortion and thermal drift in low-cost audio assemblies.
Frequently Asked Questions
S8550 vs SS8550 - same part?
Same device family. SS8550 is the vendor ordering prefix used by Diodes Incorporated and onsemi (for example SS8550DTA); S8550 is the generic Asian marking. Ratings are identical (-25V, -1.5A, 1W). Lock the vendor code and gain band on your BOM for repeatable gain matching.
S8550 vs 2N3906 - when do I need the bigger part?
Above about 200mA of continuous collector current. 2N3906 is a -200mA small-signal part; S8550 handles -1.5A with 1W dissipation and keeps hFE above 40 at -800mA. For relay coils, small speakers and motor loads in the 0.3-1.5A range, S8550 is the right choice.
How do I match S8550 with S8050 in a push-pull stage?
Order both from the same vendor and the same gain band (for example S8050 C-band with S8550 C-band), measure hFE on a sample of each lot, and keep the emitter resistors symmetric. Matched bands keep crossover distortion and quiescent current stable over temperature.
Can the S8550 switch a 12V relay coil at 400mA?
Yes comfortably: -25V VCEO covers 12V plus inductive kickback if you add a flyback diode, and -400mA is well inside the -1.5A rating. Drive the base with about -40mA (forced beta 10) for saturation, and add a base-emitter resistor to guarantee turn-off.
Why is the S8550 counterfeit-prone and how do I verify?
Its volume in audio and charger products makes remarked and no-name dies common. Curve-trace hFE at IC = -100mA (genuine: 85-300 in the stated band), verify VCE(sat) under -0.5V at -800mA/-80mA, and check breakdown beyond -25V. Clones typically show low gain and high saturation voltage.
What is the MOQ and lead time?
MOQ is 2,000 pcs fan-fold (CTA/DTA) or 10,000 pcs bulk box (CBU/DBU) for Diodes Inc SS8550; 100 pcs loose for prototypes. Shenzhen stock ships same day to 2 days; authorized replenishment is 6-10 weeks.
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