TIP35C NPN Power Transistor (100V-25A )

Description

The TIP35C is a high-power, high-current NPN bipolar junction transistor. Similar to the TIP41C mentioned previously, the TIP35C is NOT a Darlington transistor.

It is a high-performance, single-stage power BJT built to handle substantial currents. Because it is a single-stage device, it offers a much lower saturation voltage than an equivalent Darlington, which is essential for managing the heat generated at high current levels.

Key Specifications

Critical Design Differences: TIP35C vs. Darlington

Since the TIP35C lacks the internal “Darlington” stages, its behavior is distinct:

• Efficiency: Because $V_{CE(sat)}$ is relatively low (1.8V at 15A), the transistor is significantly more efficient than a Darlington. For example, at 15A, a Darlington might drop 2.5V–3V, dissipating 37W–45W. The TIP35C drops only 1.8V, dissipating 27W. That 10W–18W difference is the difference between a cool device and one that requires an massive, expensive heatsink.

• Complex Drive Requirements: This is the most important trade-off. With an $h_{FE}$ as low as 15 at high currents, you cannot drive this directly from a microcontroller. To switch 20A, you would need roughly $20A / 15 \approx 1.33A$ of base current. A standard Arduino pin only outputs 20–40mA. You must use a “driver” stage (a smaller transistor) to amplify the control signal first.

Implementation Recommendations

1. Thermal Management: With a 125W power rating, this device is capable of handling serious power, but it is effectively useless without a heavy-duty heatsink. When dealing with 25A, you must use thermal grease and a high-surface-area heatsink, likely with active fan cooling.

2. Driver Stage (The “Darlington” Substitute): To control a TIP35C from a microcontroller, use a standard NPN signal transistor (like a 2N2222 or TIP41C) to drive the base of the TIP35C. This creates a “discrete” Darlington pair, which gives you the high gain of a Darlington with the high efficiency of a single-stage power transistor.

3. High-Current Path: At 25A, standard breadboards and thin jumper wires will melt. You must use heavy-gauge wire, solid PCB traces with added solder reinforcement, and high-current screw terminals for all connections.

Common Applications

• High-Power Linear Power Supplies: Used as the pass element to regulate large amounts of current.

• Audio Power Amplifiers: Found in the output stages of high-wattage amplifiers where low distortion and high current are needed.

• Inverters and Motor Controllers: Used in high-current switching applications where efficiency is paramount.