This article documents a compact, mirrored, dual‑channel high‑side driver designed for 12 V pallet magnets using the IRF9520 P‑channel MOSFET. Each channel includes a gate network, flyback protection, indicator LED, and a manual test button. The design is optimized for clarity, repairability, and modularity.

Overview

Each channel uses an IRF9520 P‑channel MOSFET as a high‑side switch, meaning the MOSFET sits between the +12 V supply and the magnet. Pulling the gate low turns the magnet on; releasing the gate allows the pull‑up resistor to turn the MOSFET off.

The circuit includes:

• A 10 kΩ gate pull‑up (default OFF)
• A 100 Ω gate series resistor (clean switching)
• A 1N4001 flyback diode across the magnet
• A channel‑colored LED + resistor for visual indication
• A momentary test button that fires the magnet without external control
• Mirrored Blue and Green channels for easy layout and troubleshooting

This driver is suitable for 12 V pallet magnets up to ~2 A.

Parts List (per channel)

Semiconductors

• 1 × IRF9520 P‑channel MOSFET (TO‑220)
• 1 × 1N4001 flyback diode
• 1 × LED (Blue or Green)
• 1 × LED resistor (1 kΩ for Blue, 1.5 kΩ for Green)

Gate Network

• 1 × 10 kΩ gate pull‑up resistor
• 1 × 100 Ω gate series resistor

User Interface

• 1 × Momentary test button (normally open)

Connectors / Wiring

• 2‑pin terminal for magnet (+ and −)
• 2‑pin terminal for control input (signal and ground)
• +12 V and GND rails on the board

How the Circuit Works

High‑Side Switching

The IRF9520 is wired with:

• Source → +12 V
• Drain → Magnet +
• Magnet − → Ground

When the gate is pulled low, the MOSFET turns on and supplies +12 V to the magnet.

Gate Network

• A 10 kΩ pull‑up keeps the MOSFET off by default.
• A 100 Ω series resistor protects the gate and reduces switching noise.
• The control input or test button pulls the gate low to activate the magnet.

Flyback Protection

A 1N4001 diode is placed directly across the magnet:

• Cathode → Magnet + (MOSFET drain)
• Anode → Magnet − (ground)

This clamps the inductive kick when the magnet turns off.

Indicator LED

The LED and its resistor connect from +12 V to the MOSFET drain.
When the MOSFET turns on and the drain drops toward ground, the LED lights.

Assembly Instructions

1. Prepare the Power Rails

• Establish a +12 V rail and a ground rail on the board.
• Keep these rails clean and well‑defined for both channels.

2. Install the IRF9520 MOSFETs

For each channel:

• Pin 1 (Gate) → Gate network
• Pin 2 (Drain) → Magnet + and diode cathode
• Pin 3 (Source) → +12 V rail

Ensure the MOSFETs face the same direction for mirrored layout.

3. Build the Gate Network

For each channel:

1. Solder a 10 kΩ resistor from Gate → +12 V (pull‑up).
2. Solder a 100 Ω resistor from Gate → Control Input.
3. Connect the test button between Gate → Ground.

4. Add the Flyback Diode

Across the magnet terminals:

• Banded end (cathode) → MOSFET drain / magnet +
• Non‑banded end (anode) → Ground / magnet −

5. Install the Indicator LED

• LED anode → +12 V
• LED cathode → LED resistor → MOSFET drain

Use:

• 1 kΩ for Blue LED
• 1.5 kΩ for Green LED

6. Connect the Magnet Terminals

Each channel gets a 2‑pin terminal:

• Pin 1 → MOSFET drain (magnet +)
• Pin 2 → Ground (magnet −)

7. Connect the Control Inputs

Each channel gets a 2‑pin control header:

• Signal → 100 Ω gate resistor
• Ground → Board ground

8. Final Checks

• Verify MOSFET orientation
• Confirm diode polarity
• Ensure gate pull‑ups are connected to +12 V
• Press test buttons to confirm each magnet fires
• Check LEDs light during activation

Diagram

here's an ASCII representation of this circuit: 

                   +12V RAIL                      |        -------------------------------------        |                                   |   [IRF9520]                             [IRF9520]   Blue MOSFET                           Green MOSFET   (P‑channel)                           (P‑channel)        |                                   |   Source (S)                           Source (S)        |                                   |        +-------------+12V------------------+        |   Drain (D) ---------------------.     Drain (D) ---------------------.        |                         |          |                         |        |                     [MAGNET]       |                     [MAGNET]        |                     Blue +         |                     Green +        |                         |          |                         |        |                    (to GND)        |                    (to GND)        |                         |          |                         |        |                     [DIODE]        |                     [DIODE]        |                 1N4001 (across)    |                 1N4001 (across)        |   Gate (G) <---100Ω--- Control In      Gate (G) <---100Ω--- Control In        |                                   |       10kΩ                                 10kΩ        |                                   |       +12V                                 +12V        |                                   |   [TEST BUTTON]                        [TEST BUTTON]        |                                   |       GND                                 GND   LED + Resistor                      LED + Resistor   (Blue channel)                      (Green channel)   +12V ---[LED]---[1kΩ]--- Drain      +12V ---[LED]---[1.5kΩ]--- Drain

Performance Notes

• The IRF9520 is not a logic‑level MOSFET, but at 12 V it fully turns on when the gate is pulled to ground.
• At 2 A magnet current, the MOSFET dissipates roughly 1–2 W, which is acceptable for short organ note durations.
• The mirrored layout makes troubleshooting straightforward: if one channel works, the other should match it exactly.