LED Strip Control Design
0:34
Below is a concise design outline for driving two LED rails (warm white and cool white) at 24 V, each drawing up to 400 mA:
1. Discrete MOSFET Drive (Low-Side Switching)
-
Power Rail:
- Supply a stable 24 V rail capable of at least 800 mA total (to cover both warm and cool strips at full brightness).
-
MOSFET Selection:
- Use two N-channel MOSFETs with each drain connected to one LED rail’s negative terminal.
- Common anode of the LED strip goes to +24 V.
- Key parameters for each MOSFET:
- Drain–Source Voltage ≥ 30 V.
- Continuous Drain Current ≥ 1 A (for margin over 400 mA).
- Low R_DS(on) to minimize heat dissipation.
-
Gate Drive / PWM Control:
- Connect MOSFET gates to a microcontroller PWM output (possibly through a gate driver if logic-level gating is insufficient).
- PWM frequency in the hundreds of Hz or higher is typical for LED dimming.
- Add a pull-down resistor (e.g., Rxx) on each gate to ground to prevent floating gates when the microcontroller is off.
-
Current Sense (Optional):
- If you need current feedback or fault detection, place a small sense resistor (e.g., 0.1 Ω–0.2 Ω) in series with each MOSFET source.
- Amplify the sense voltage via a low-offset op amp or dedicated current-sense amplifier.
-
Flyback or Snubber (Rarely Needed):
- Because these strips are resistive LED strings rather than inductive loads, a simple snubber is generally not required. However, if you notice voltage spikes or EMI, consider adding small RC snubbers across MOSFET drains and sources.
2. Integrated Dual-Channel LED Driver
-
Driver IC Features:
- A dual-channel driver with two low-side switches or current regulators, each supporting up to 400–500 mA from a 24 V supply.
- Integrated PWM dimming inputs or digital interface (I²C, SPI) for brightness control.
- Built-in thermal shutdown, short-circuit, or over-current protection.
-
Wiring:
- The driver’s two channel outputs each connect to one LED rail negative terminal.
- The LED strip positive terminals go to the +24 V rail.
- Keep an input capacitor near the driver’s supply pin if recommended by its datasheet.
-
Thermal Considerations:
- Drivers with integrated MOSFETs typically have robust thermal protection but may need heat sinking if running at higher power or enclosed in a small space.
Next Step
Measure or estimate the actual current for each strip segment (warm + cool at full brightness) to confirm the <400 mA target. This ensures you select properly rated MOSFETs or drivers. Once confirmed, you can finalize the power supply capacity and any heat dissipation provisions.
0:37
Below are a few logic-level N-channel MOSFET families commonly used to switch ≤1 A at 24 V:
-
- Logic-level gate threshold, low R_DS(on) for higher efficiency.
-
- Small SMD package, suitable for up to ~1 A with proper heat dissipation.
-
- Through-hole “classic” MOSFET, ample current rating with low conduction losses.
-
- Compact package, low gate charge and R_DS(on), good for moderate currents.
Any of these (or similar) logic-level N-channel FETs with a drain–source rating ≥ 30 V and an on-state current ≥1 A will work well for your 24 V, 400 mA LED strip switching application.
Compare MOSFET specs
Find similar MOSFET families
Select a specific MOSFET
Welcome 👋
Flux helps you build PCBs faster with an AI teammate!
Create your account to collaborate, stay updated, fork your own version, and get instant answers from our AI agent.