Mfr Part #:

BUL128-K

Q: What is the DC current gain (hFE)?

The DC current gain is minimum 14 at IC=2A, VCE=5V, with group selections available: Group A 14-25, Group B 28-40.

Q: What are the switching times?

Storage time is 1.5µs typical (3µs max) and fall time is 0.2µs typical (0.4µs max) under resistive load conditions.

The BUL128-K is an NPN power transistor from STMicroelectronics with a VCEO of 400V and collector current rating of 4A. It comes in a TO-220 through-hole package.

✓ Total Stock: 18,500 pcs

$ Price Range: $0.45

BUL128-K Available from 1 distributor

✓ Authorised

✓ Non-Authorised

Distributor		Stock	Pricing	MOQ	PKG	Lead Time	Date Code	On Order Quantity	On Order Delivery
Hybrid Electronics ✓ Non-Authorised Inventory information	18,500 pcs On Request	18500 pcs	On Request	1	On Request	On Request	1134	On Request	On Request

BUL128-K Description

Short technical summary and product information.

The BUL128-K is a high voltage fast-switching NPN power transistor manufactured by STMicroelectronics using multi epitaxial planar technology. It features a cellular emitter structure with planar edge termination to enhance switching speeds while maintaining wide RBSOA. The device is designed for use in lighting applications such as electronic ballasts for fluorescent lighting, as well as low cost switch-mode power supplies.

Key electrical specifications include a collector-emitter sustaining voltage (VCEO(sus)) of 400V, a collector-emitter voltage with base shorted (VCES) of 700V, and a continuous collector current rating of 4A (8A peak). The DC current gain (hFE) is minimum 14 at 2A, 5V, with group selections offering tighter ranges. Saturation voltages are low, with VCE(sat) typically 0.5V at 0.5A collector current. Switching performance is characterized by storage time of 1.5µs typical and fall time of 0.2µs typical under resistive load.

The transistor is housed in a standard TO-220-3 through-hole package, suitable for heatsink mounting. Thermal resistance from junction to case is 1.78°C/W, allowing up to 70W power dissipation at 25°C case temperature. The operating junction temperature range is -65°C to 150°C. Compliance with RoHS3 and REACH is indicated but unverified.

BUL128-K Quick Information

Product Type: Bipolar (BJT) Single Transistor

Canonical Name: BUL128-K NPN Power Transistor

Subcategory: High Voltage Fast-Switching

BUL128-K Compliance

RoHS Status: RoHS Compliant

Moisture Sensitivity Level (MSL): 1 Unlimited

REACH Status: REACH Unaffected

BUL128-K Estimated Pricing

Qty	Low	High
1,750+	$0.45	$0.45

Estimated market price range - modelled values for guidance only, not live distributor offers.

BUL128-K Features

High voltage NPN power transistor.
400V collector-emitter sustaining voltage.
4A continuous collector current rating.
Fast switching with low storage time.
TO-220 through-hole package.

BUL128-K Applications

Ideal for electronic ballasts in lighting.
Used in low cost switch-mode power supplies.
Suitable for high voltage switching circuits.
Designed for reliable operation in power systems.

BUL128-K FAQs

7 frequently asked questions generated from this part’s specifications.

What is the operating voltage of the BUL128-K?

The collector-emitter voltage (VCEO) is 400V maximum, and the collector-emitter voltage with base shorted (VCES) is 700V maximum.

What package does the BUL128-K come in?

The BUL128-K is available in a TO-220-3 through-hole package.

What is the operating temperature range?

The operating junction temperature range is -65°C to 150°C.

Is the BUL128-K RoHS compliant?

The BUL128-K is listed as RoHS3 Compliant, but this information is unverified.

What is the collector current rating?

The maximum continuous collector current is 4A, with a peak current of 8A (tp<5ms).

What is the DC current gain (hFE)?