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🌡️ Over Temperature Sensor Circuit – Smart Solar Inverter Protection ☀️

In modern solar inverter systems, protecting the power electronics from overheating is essential for reliability and long life. This over-temperature sensor circuit is designed to automatically detect high temperature conditions and trigger protective actions such as fan activation or system shutdown.

The circuit is built around an NTC thermistor and an LM393 comparator:

The NTC thermistor (TH1) continuously senses the inverter’s temperature. As the temperature increases, its resistance decreases, changing the voltage across it.

The LM393 comparator compares this voltage with a fixed reference voltage generated by a resistor divider network.

When the sensed voltage drops below the reference level (indicating an overheat condition), the comparator output switches LOW.

This output is then sent to the microcontroller, which can turn ON the cooling fan or shut down the inverter to prevent damage.

To improve stability and noise immunity, filter capacitors (C18 & C19) are used at both the sensing and output stages. The pull-up resistor (R21) ensures a clean logic-level output compatible with microcontroller input pins.

✅ Features:

Accurate and fast temperature response

Automatic fan ON/OFF or shutdown control

Compact and reliable circuit design

Ideal for solar inverters, battery chargers, and power control systems

This simple yet effective design helps protect your inverter from overheating and enhances system safety and lifespan.

📞 Contact: 03214799117

🔋 Understanding the TLP250 Gate Driver – Complete Explanation

The TLP250 is an optically isolated gate driver IC widely used in solar inverters, motor drives, and power electronics. Its main purpose is to isolate and amplify control signals from a microcontroller (like the dsPIC30F2010) to safely and efficiently drive high-power MOSFETs or IGBTs.

Let’s break down how it works 👇

⚙️ 1. Why We Need a Gate Driver

Microcontrollers generate low-voltage logic signals (usually 3.3V or 5V), which are not strong enough to drive the gate of power switches directly.
MOSFETs and IGBTs need 10–15V gate voltage and higher current to switch quickly and efficiently.

The TLP250 acts as a bridge between the low-voltage control circuit and the high-voltage power circuit — providing both signal isolation and amplification.

💡 2. How Optical Isolation Works

Inside the TLP250, there’s a tiny infrared LED on the input side and a photodiode transistor array on the output side.
When the LED turns ON, light is transmitted to the output side — but there’s no electrical connection between them.

This light-based communication provides complete galvanic isolation, protecting the sensitive MCU from the high-voltage power stage of the inverter.

🔌 3. Input Side (Pins 2 & 3)

The MCU output pin (for example, PWM signal) is connected to the input pin (Pin 2) of the TLP250 through a 270Ω resistor (R40).

This resistor limits the current flowing through the internal LED to around 10–15mA.

When the MCU output goes HIGH → LED inside TLP250 turns ON → Output transistor is activated.

⚡ 4. Output Side (Pins 5, 6, 7, 😎

The output section is powered by VCC (typically +15V).

When the LED is ON, the TLP250 output goes HIGH (~15V) — turning the MOSFET/IGBT ON.

When the LED is OFF, the output goes LOW (~0V) — turning the switch OFF.

The output can source or sink up to ±1.5A, which ensures the power transistor gate charges and discharges quickly for efficient switching.

Crystal Oscillator circuit diagram in Solar Inverter

The circuit provide stable clock signal to MCU(dsPIC30f2010) to generate PWM/MPPT.

Main Components:
Y1 - Crystal (7.3728 MHz)
This quartz crystal sets the oscillation frequency for the MCU.
The dsPIC30F2010 uses this as its primary clock source.
7.3728 MHz is a common frequency because it divides cleanly into standard baud rates (useful for UART communication).

C4 and C5 - Load Capacitors (27 pF each):
These two capacitors, connected from each crystal pin to ground, form a parallel resonant circuit.
They stabilize the oscillation and ensure the crystal runs at its rated frequency.
Their value (22-33 pF typical) depends on the crystal's specified load capacitance (CL), and the PCB stray capacitance.
The Approximate formula is
C_{load}=(C4 x C5)/(C4+C5) +C_{stray}
Example: if crystal CL = 18 pF and stray ≈ 3 pF, then 27 pF caps are suitable.

Working Principle:
When the dsPIC30F2010's oscillator pins (OSC1 and OSC2) are connected to this circuit:
The MCU's internal oscillator amplifier drives the crystal.
The crystal resonates at its natural frequency (7.3728 MHz here).
The output is a stable sinusoidal or square wave clock.
The MCU divides this clock internally to derive system and instruction clocks.

In Solar Inverter Use:
The accurate clock is essential for PWM timing for inverter switching.
Precise ADC sampling.
Stable communication (UART, SPI, etc.).
Any drift in frequency could cause phase or timing errors in the inverter control algorithm.

Description:
>C1,C2,C3 capacitor makes RC low pass filter to clean mechanical noises and provide clean signal to MCU
Debounce time constant:
T=R X C= 10k*0.1uF=1m sec
So the input takes around 1 ms to settle, effectively removing short glitches caused by contact bounce.

>R2,R3,R4 makes pull up logic (1 continusely to mcu) when pressed button than provide 0 to MCU

Description:
This Circuit Is designed such that it will Calculate the Voltages of PV .
(R37+R38+R39)||R36 => 300k||2.9k
=> As we know that Voltage Devider Formula

V_{mcu}=(2.9k/302.9k)*PV
Suppose PV=180V DC => 0.009574*180=1.7233V this will appear at MCU

Maximum Rating:
5/0.009574=522.3V maximum PV we can calulate is 522.3V

Zenor Diode :
To limit the value maximum to 5V to protect MCU.

C28 Capacitor:
bypass / filter capacitor from the measurement node to ground. It smooths high-frequency noise and stabilizes the node when the ADC samples.

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📞 Contact: 0321-4799117