| Symbol | Part | Typical Value | Function | |--------|------|---------------|----------| | C1 | Input Decoupling Capacitor (X7R ceramic) | 10 µF – 22 µF, 10 V | Smooths out supply ripples, provides a local energy reservoir for transient load spikes. | | R1 | Series Input Resistor | 0.1 Ω – 0.33 Ω (1 % tolerance) | Limits inrush current when the device powers up, helps protect the LAD402P’s internal MOSFET from stress. | | D1 | Reverse‑Polarity Protection Diode (Schottky) | 1 N5819 or similar | Prevents catastrophic damage if Vin is accidentally connected reversed. Schottky is used for its low forward voltage (≈0.3 V) to minimize loss. | | C3 (optional) | High‑Frequency Bypass (0.1 µF) | 0.1 µF, 6 V | Placed close to the regulator pins to shunt HF noise to ground. |
Design tip: If you’re running from a noisy source (e.g., a switching buck converter), increase C1 to 47 µF and add a Ferrite bead (L1) of 600 Ω at 100 kHz in series with Vin. This suppresses high‑frequency interference that could otherwise modulate the output.
| Desired Change | What to Modify | Why | |----------------|----------------|-----| | Higher Output Voltage (up to 6 V) | Increase R2 or decrease R3 while keeping the ratio (1+R2/R3 = Vout/Vref). | The LAD402P’s Vin must stay at least 0.5 V above Vout; ensure Vin ≥ Vout + 0.5 V. | | Lower Output Current (e.g., 500 mA) | Insert a larger sense resistor (R5 = 1 Ω) to bring the internal current‑limit down. | Protect delicate downstream loads. | | Battery‑Powered Design | Choose low‑ESR, high‑temperature capacitors, and add a reverse‑polarity MOSFET (P‑channel) instead of a diode to reduce loss. | Batteries are sensitive to voltage drop; MOSFET offers < 0.1 V loss. | | Ultra‑Low Noise Audio Amplifier | Add an LC filter after Vout (e.g., 10 µH + 4.7 µF) and use NP0/C0G capacitors for C2. | Improves PSRR and reduces audible hiss. |
Use one NO contact to energize a pilot light when the contactor pulls in. lad402p schematic top
This is a break-before-make action, identical to a standard relay but optimized for motor inrush currents.
To appreciate the LAD402P schematic top, compare it to similar models:
| Model | Contact Config | Top Schematic Difference | |-------|----------------|--------------------------| | LAD402P | 2 NO + 2 NC | Standard simultaneous action | | LAD4P2 | 1 NO + 1 NC (early make) | NO closes 2ms before NC opens | | LAD4P3 | 1 NO + 1 NC (late break) | NC opens 2ms before NO closes | | LAD401P | 1 NO + 1 NC | Only one set of contacts physically smaller | | LAD4P4 | 4 NO | All contacts NO — used for purely sealing circuits | | Symbol | Part | Typical Value |
If your top schematic requires sequential behavior, the LAD402P is not the correct choice. Use LAD4P2 or LAD4P3.
The LAD402P is a voltage‑adjustable regulator; the output voltage is set by a simple resistor divider.
| Symbol | Part | Typical Value | Function | |--------|------|---------------|----------| | R2 | Upper Divider Resistor | 2.2 kΩ – 5 kΩ | Works with R3 to set Vout = Vref × (1 + R2/R3). Vref for LAD402P ≈ 1.2 V. | | R3 | Lower Divider Resistor | 1 kΩ – 2.2 kΩ | Together with R2 defines the output voltage. | | C2 | Compensation Capacitor | 0.1 µF – 1 µF | Placed from the feedback node (junction of R2/R3) to ground; adds phase margin and reduces output ripple. | | R4 (optional) | Load‑Adjust Resistor | 10 Ω – 100 Ω | Small resistor in series with the load to improve transient response; not required in the reference design. | | Desired Change | What to Modify |
How to calculate Vout:
[ V_out = V_ref \times \left(1 + \fracR2R3\right) ]
For a 5 V output, you could pick R2 = 3.3 kΩ, R3 = 1 kΩ:
[ 5 V = 1.2 V \times (1 + 3.3k/1k) ≈ 5.04 V ]
Stability note: The LAD402P is internally compensated for loads > 200 mA. If you anticipate lighter loads (< 200 mA), increase C2 (e.g., to 2 µF) or add a small series output resistor (R5, 0.1 Ω) to guarantee sufficient ESR for stability.