[better] - Sn51dp Datasheet

According to internal block diagrams from older datasheets, the SN51DP uses a bipolar junction transistor (BJT) as the power switch, not a MOSFET. This explains its higher saturation voltage (0.8V typical) compared to modern MOSFET-based converters.

Exceeding these values will destroy the IC. These are non-recoverable limits. sn51dp datasheet

| Pin Number | Pin Name | Description | | --- | --- | --- | | 1 | VCC | Power supply voltage (5V) | | 2 | GND | Ground | | 3 | DIN | Differential input | | 4 | DOUT | Differential output | | 5 | RIN | Receiver input | | 6 | ROUT | Receiver output | | 7 | RE | Receiver enable | | 8 | DE | Driver enable | According to internal block diagrams from older datasheets,

SN51DP Pin 4 (Output) → Power Triac Gate (via 180–330 Ω resistor) SN51DP Pin 6 (Output) → Power Triac MT2 (or neutral line) Power Triac MT1/MT2 in series with load on AC line. These are non-recoverable limits

: You can find current availability through distributors like IC-Components Thermal Management

| Symptom | Likely Cause | Solution | | :--- | :--- | :--- | | No output, VIN present | Short between pins 1-2 or 2-3 | Replace IC; check D1 and L1 for shorts | | Output voltage low or pulsing | Current limit triggering (overload or inductor saturation) | Reduce load or replace L1 with higher saturation rating | | Excessive ripple voltage | Bad output capacitor (high ESR) | Replace C2 with low-ESR type | | IC hot even at light load | Oscillator dead or catch diode open | Replace D1; check compensation pin | | Output voltage incorrect | Resistor divider damaged or FB pin leakage | Clean PCB; replace R1/R2 |

Constantly "feels" the current flow, ensuring the LEDs don't burn out from over-excitement. Pin 8 (COMP):