Function of the TEC Controller

Operating Principle

The TEC controller regulates the output current depending on:

The value of the connected NTC (actual temperature)
The setting of the TEMP potentiometer (target temperature)

Temperature Control vs. Monitoring

Temperature Relationship

Nominal Temperature (TEC Target)
        ↓
    TEC regulates to this value
        ↓
        ↓
    Threshold Temperature
        ↓
    Safety shutdown at this value

Example for 25°C setting:

Nominal (TEC target): 25°C
Threshold (Shutdown): 35°C
Hysteresis (Re-enable): 31°C

TEC Activation Logic

When TEC Activates

The TEC driver output is active when:

The set nominal temperature is about to be exceeded
Temperature is rising toward the nominal setpoint
Active cooling is required

TEC Behavior During Shutdown

If the threshold temperature is reached:

✅ Laser is disabled (safety shutdown)
✅ TEC controller output remains active
✅ TEC continues cooling
✅ Cooling until temperature equals nominal temperature
✅ Then TEC may turn off or regulate

Operating States

State 1: Temperature Below Nominal

Actual Temperature < Nominal Temperature
        ↓
    TEC Output: OFF
    TEC LED: OFF
    Laser: ENABLED (if other conditions met)

Example:

Nominal: 25°C
Actual: 20°C
TEC: OFF (no cooling needed)

State 2: Temperature Approaching Nominal

Actual Temperature ≈ Nominal Temperature
        ↓
    TEC Output: ACTIVE (proportional)
    TEC LED: ON
    Laser: ENABLED

Example:

Nominal: 25°C
Actual: 24-26°C
TEC: Active regulation

State 3: Temperature Above Nominal (Below Threshold)

Nominal < Actual Temperature < Threshold
        ↓
    TEC Output: ACTIVE (full cooling)
    TEC LED: ON
    Laser: ENABLED

Example:

Nominal: 25°C
Threshold: 35°C
Actual: 30°C
TEC: Full cooling power
Laser: Still enabled

State 4: Temperature Exceeds Threshold

Actual Temperature ≥ Threshold
        ↓
    Laser: DISABLED (safety shutdown)
    TEC Output: REMAINS ACTIVE
    TEC LED: ON
    TEMP LED: FLASHING
        ↓
    TEC cools until Actual = Nominal
        ↓
    TEC may turn off or regulate at nominal

Example:

Nominal: 25°C
Threshold: 35°C
Actual: 36°C (exceeded threshold)
Laser: OFF
TEC: Continues cooling
Target: Cool back to 25°C

Control Characteristics

Temperature Dependencies

Relationship:

Set Nominal Temperature
        ↓
    Automatically determines:
    ├─ Threshold Temperature
    └─ Hysteresis Temperature

Control Loop

NTC measures temperature
        ↓
    Compare to Nominal Setting
        ↓
    Calculate Error
        ↓
    Adjust TEC Current
        ↓
    TEC Cools (or off if below nominal)
        ↓
    Temperature Changes
        ↓
    Loop repeats (continuous)

TEC Current Control

Output Current Behavior

The TEC output current is proportional to the temperature error:

TEC_Current ∝ (Actual_Temp - Nominal_Temp)

When:

Temp slightly above nominal → Low TEC current
Temp significantly above nominal → High TEC current (up to 2A max)
Temp at or below nominal → TEC off

TEC LED Indication

TEC State	TEC LED	Meaning
Not cooling	OFF	Temperature at or below nominal
Cooling active	ON	Temperature above nominal, TEC regulating

Practical Operation Examples

Example 1: Startup from Room Temperature

Initial Conditions:

Room temperature: 22°C
Nominal setting: 25°C
Threshold: 35°C

Sequence:

Power on
Temp = 22°C (below nominal)
TEC: OFF
Enable laser
Laser generates heat
Temp rises toward 25°C
At ~24°C: TEC starts activating
Temp reaches 25°C: TEC regulates to maintain
TEC LED: ON (active regulation)

Example 2: High Ambient Temperature

Initial Conditions:

Ambient: 30°C
Nominal: 25°C
Threshold: 35°C

Sequence:

Power on
Temp = 30°C (above nominal, below threshold)
TEC: Immediately active (full cooling)
TEC LED: ON
Temperature drops toward 25°C
Reaches 25°C: TEC continues regulating
Laser can be enabled safely

Example 3: Overtemperature Event

Conditions:

Nominal: 25°C
Threshold: 35°C
Inadequate heat sinking

Sequence:

Operating at 25°C
High laser power generates excess heat
Temp rises despite TEC cooling
Temp reaches 35°C (threshold)
Laser DISABLED immediately
TEMP LED: FLASHING
TEC: Remains active, full cooling
Temp drops
Reaches ~31°C (hysteresis)
Can re-enable (depends on operating mode)
TEC continues cooling to 25°C
Stabilizes at 25°C

Thermal Dynamics

Response Time

Factors affecting response:

TEC size and power
Thermal mass of laser assembly
Heat sink capacity
Ambient temperature
Laser power dissipation

Typical settling time: 30 seconds to several minutes

Stability Considerations

For stable temperature control:

Requirements:

✅ NTC close to laser (minimal thermal lag)
✅ TEC in good thermal contact with laser
✅ Adequate heat sink on TEC hot side
✅ Proper thermal paste/interface
✅ Minimal air gaps

Thermal Oscillation

Symptoms:

Temperature cycling above/below setpoint
TEC LED flashing on/off
Unstable laser output

Causes:

NTC too far from laser
Excessive thermal lag
Poor thermal coupling
Undersized heat sink

Solutions:

Reposition NTC closer
Improve thermal contact
Add thermal mass
Upgrade heat sink
Reduce thermal resistance

Power Consumption

TEC Power Dissipation

Maximum TEC power:

P_TEC_max = V_IN × 2A

Example:

V_IN = 12V
I_TEC_max = 2A
P_TEC_max = 24W

Total System Power

P_TOTAL = P_LASER + P_DRIVER + P_TEC

Example calculation:

Laser: 5W
Driver: 2W
TEC (max): 24W
Total: 31W

Optimization Tips

For Best Temperature Control

Thermal Design:
- Minimize thermal resistance
- Use thermal paste
- Ensure good contact
NTC Placement:
- As close to laser as possible
- Good thermal contact
- Protected from damage
TEC Selection:
- Match TEC capacity to heat load
- Consider ambient conditions
- Verify voltage compatibility
Heat Sinking:
- Adequate size for TEC hot side
- Good airflow if needed
- Monitor heat sink temperature

For Stable Operation

✅ Allow sufficient warm-up time
✅ Maintain stable ambient temperature
✅ Ensure adequate power supply capacity
✅ Monitor TEC current draw
✅ Check for thermal runaway conditions

Monitoring TEC Performance

Indicators of Proper Operation

✅ TEC LED behavior matches temperature
✅ Temperature stabilizes at setpoint
✅ No temperature oscillation
✅ Adequate cooling capacity
✅ Threshold never reached during normal operation

Signs of Problems

❌ TEC always ON at maximum
❌ Cannot reach nominal temperature
❌ Frequent threshold shutdowns
❌ Temperature oscillation
❌ TEC LED behavior erratic

Safety Considerations

TEC Polarity

Always verify:

TEC+ to TEC positive terminal
TEC- to TEC negative terminal
Check TEC datasheet for wire colors

Thermal Runaway Protection

The threshold temperature provides protection against:

TEC failure
Inadequate heat sinking
Reversed TEC polarity
Excessive ambient temperature

The laser will be disabled before damage occurs.