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IronOS-powered soldering irons use PWM-controlled resistive heating elements. Understanding the power delivery system is essential for optimizing performance and troubleshooting power-related issues.

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Power Fundamentals

Soldering irons function as a resistor connected to your power source through an electronically-controlled switch. The electronics can only turn the heating element on or off - they cannot vary the power directly.
Critical Insight: Power delivered to the tip is 100% controlled by supply voltage. Higher voltage = Higher performance.

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Basic Electrical Equations

When the switch is on: 
P (watts) = V (volts) × I (amps)
I (amps) = V (volts) ÷ R (ohms)

Combining these:
P (watts) = V² ÷ R (ohms)
Key Takeaway: Power is proportional to voltage squared. Doubling voltage quadruples power delivery.

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Tip Resistance Values

Tip resistance is a fixed constant that determines power characteristics:
DeviceTip TypeResistance
PinecilShort tip6.2 Ω
Pinecil / TS100Long tip8.0 Ω
TS80(P)Standard4.5 Ω
Pinecil and TS100 perform poorly on 12V power supplies and may display a Thermal Runaway warning indicating insufficient power delivery.

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Power Output Calculator

Use an Ohm calculator to determine power output for your configuration.

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Power Output Table

Power SourceVoltageTip ΩCurrentPower Output
USB QC3.09V4.5 Ω2.0A18W
USB-C PD12V4.5 Ω3.0A32W
USB-C PD20V8.0 Ω2.5A50W
USB-C PD20V6.2 Ω3.2A64W
DC Barrel24V8.0 Ω3.0A72W
DC Barrel24V6.2 Ω3.8A92W
EPR PD3.128V8.0 Ω3.5A98W
EPR PD3.128V6.2 Ω4.5A126W
Performance Recommendation: For optimal performance, use 20V USB-PD or higher voltage sources. 28V EPR PD3.1 provides maximum power delivery.

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Output Control System

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Hardware Components

  1. P-MOSFET: Switches power to the tip
  2. Transistor circuit: Controls the MOSFET
  3. MCU (STM32): Runs PID control loop and generates PWM signal

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Control Flow

PID Controller → PWM Signal → Transistor Circuit → P-MOSFET → Tip Power
The MCU controls PWM output proportional to the PID control loop output, regulating tip temperature.

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Temperature Measurement Timing

To measure the tiny thermocouple voltage, the output must be turned off temporarily:
  1. FET turns off (heating stops)
  2. Recovery period: Tip capacitance discharges, op-amp exits saturation
  3. ADC samples: 8 rapid samples of op-amp output
  4. PWM resumes: Heating continues
This creates a dead time in the output signal during each measurement.
See Temperature Control for detailed information on measurement complexity.

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Sampling Tradeoff

The firmware balances two competing needs:
  • More frequent sampling: Better temperature stability
  • Less frequent sampling: Higher maximum power delivery

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Soldering Iron Load Characteristics

Soldering irons present a unique challenge for power supplies:
Rapid Load Changes: Unlike laptops or phones that gently ramp power, soldering irons switch rapidly from 0 to full power and back. This can trip protection circuits on some power supplies.

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Load Pattern

Typical Device:  [====== Gradual Ramp ======]
Soldering Iron:  [█████ ON] [   OFF   ] [█████ ON]
This rapid switching can cause issues with:
  • Multi-port chargers at full capacity
  • Budget power supplies with sensitive protection
  • “Smart” chargers with complex protocol implementations

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Power Source Recommendations

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Ideal Power Supplies

Recommended: Normal, boring 60-100W PD supply. Avoid over-marketed multi-port adapters.
  • Single-port dedicated supply
  • 60W minimum for TS100/Pinecil
  • 100W for optimal performance with short tips
  • Clean PD implementation (avoid “smart” chargers)

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Multi-Port Adapter Warning

Watch out for misleading marketing:Example: “65W” adapter with:
  • Port 1: 45W
  • Port 2: 20W
Reality: Cannot deliver 65W to a single port. Maximum per-port delivery is what matters.

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Protocol Compatibility

Smarter chargers implementing multiple protocols may have quirks:
  • Shortcuts in PD implementation
  • Compatibility issues with rapid load changes
  • Protocol switching delays
For supported power standards and protocols, see Power Sources documentation.

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PWM Regulation Details

The P-MOSFET switching is controlled via PWM (Pulse Width Modulation):
  • High duty cycle: More heating power
  • Low duty cycle: Less heating power
  • 0% duty cycle: Temperature measurement period

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PID Control Integration

The PID controller calculates required power based on:
  1. Current temperature (measured)
  2. Target temperature (setpoint)
  3. Rate of change (derivative)
  4. Accumulated error (integral)
Output is translated to PWM duty cycle for the MOSFET.
See Temperature Control for PID tuning philosophy and implementation details.

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Thermal Runaway Protection

IronOS includes thermal runaway detection to protect against:
  • Insufficient power supply capacity
  • Damaged heating elements
  • Thermal coupling issues

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When it Triggers

The firmware monitors:
  • Time to reach target temperature
  • Rate of temperature increase
  • Maximum power delivery vs. measured heating
If heating is insufficient despite full power delivery, thermal runaway protection activates.
Common Cause: Using 12V power supply with 8Ω tip (only ~18W available).

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Optimization Strategies

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Maximum Performance

  1. Use highest voltage available: 28V EPR > 24V DC > 20V PD > 12V
  2. Choose appropriate tip: Lower resistance = higher power (if supply can handle current)
  3. Quality cables: E-marked cables for high-power PD, thick wires for DC
  4. Single-port supply: Dedicated power supply without port sharing

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Battery Operation

When using battery packs:
  • Check sustained discharge rating (not peak)
  • Account for voltage sag under load
  • Monitor battery temperature during use
  • Use batteries rated for high-current discharge

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