How to find the right Darlington Transistors AI guide
Written by an AI model from its trained knowledge.
What the AI looks for in Darlington Transistors
- Saturation voltage
- Expect Vce(sat) of roughly 1 to 2 V, and check the datasheet value at your load current. A Darlington can never fully saturate, so it dissipates noticeably more power than a MOSFET at the same current.
- Base-emitter turn-on voltage
- Expect about two diode drops at the base (roughly 1.2 V or more). Low-voltage logic drive and base-resistor sizing must account for this higher turn-on voltage.
- Voltage and current ratings
- Vceo should sit above the supply plus inductive spikes. Size continuous current from the package's thermal limits. Darlingtons are often used on motors and solenoids, where flyback spikes are common.
- Integrated protection
- Check whether the part includes an internal flyback diode and base-emitter resistors. These parts simplify driving inductive loads, but you should never assume they are present.
- Switching speed
- Use Darlingtons only for slow switching or low-frequency PWM. Their turn-off is slow, which raises losses at higher frequencies.
- Arrays vs discrete
- For several relays, solenoids or LEDs, consider a multi-channel Darlington driver array instead of discrete parts. Arrays integrate clamp diodes and save board space.
Brands that matter
- STMicroelectronics: Power Darlingtons and Darlington driver arrays.
- onsemi: Classic TO-220 Darlingtons and complementary pairs.
- Texas Instruments: Darlington transistor array driver ICs.
- Toshiba: Darlington driver arrays.
What to avoid
- Using a Darlington where a logic-level MOSFET would switch the same load with far less heat
- Driving inductive loads without confirming a flyback diode is present
- Fast PWM duty
Questions
Why does my Darlington run hot even well under its rated current?
Its saturation voltage of a volt or more times the load current is dissipated as heat. A logic-level MOSFET often removes the problem.