TL431 reference
TL431 adjustable shunt regulator · sinks whatever current (1–100 mA) keeps REF at 2.495 V above the anode · V_KA up to 36 V · set V_out = 2.495 × (1 + R1/R2)
Try it on the benchThe lab drops it on an empty bench and opens its datasheet card.
Typical part: TL431 shunt regulator
Pins
- REF
- A (anode)
- K (cathode)
Ratings and limits
| V_REF | 2.495 V ± 1 % |
|---|---|
| I_KA | 1–100 mA |
| V_KA | up to 36 V |
How to use it
An adjustable zener: R1 from cathode to REF, R2 from REF to anode sets V = 2.495 (1 + R1/R2). Also the feedback reference in almost every switch-mode charger.
Lessons and builds that use it
- ADC front end: reference and anti-alias filter
- 18650 battery level indicator (build)
- 12 V low-voltage battery cutoff (build)
- 65 W USB-C PD charger from scratch: mains flyback (UC3844, 800 V MOSFET, PQ2625 transformer), TL431 + PC817 feedback, PD controller (build)
- Single 18650 charger with a 3-LED charge indicator (green 80–100 %, yellow 40–79 %, red below 40 %) (build)
- Real device: phone charger, 220 V AC wall to 5 V USB (build)
- Real device: laptop charger, 220 V AC wall to 20 V with PFC (build)