TDA16846 is a key component in switching power supplies, and its pin functions are crucial for proper operation. Here's an overview of each pin: Pin 1: This pin connects to an RC network that determines the loop turn-off time and standby frequency. It plays a vital role in setting the timing parameters of the power supply. Pin 2: A capacitor is connected here, and it’s linked to the primary winding of the transformer and the drain of the switching transistor through a resistor. The resistor value affects the maximum output power of the system. Pin 3: This is the input pin for the error voltage amplifier and also serves as a zero-crossing detection point. When the input voltage exceeds 5V, it triggers a reduction in the control voltage on pin 4. Pin 4: This is the control voltage pin, connected to ground via a capacitor. The capacitor’s value determines the soft start duration and the speed of control response. Pin 5: If using a photodiode sampling circuit for error amplification and voltage regulation, this pin receives the output from the optocoupler, which helps maintain stable output voltage. Pin 6: This pin acts as a fault comparator input. If the voltage on this pin exceeds 1.2V, the power supply will shut down to protect against faults. If not used, it can be grounded. Pin 7: This pin is used to select the operating mode of the power supply. An RC network or sync signal can be connected here to set either fixed frequency or synchronized operation. Pin 8: This is an unused pin and should remain unconnected. Pin 9: This pin provides a 5V reference voltage and current, essential for internal regulation and stability. Pin 10: If the voltage on this pin exceeds 1.2V, the power supply enters protection mode, stopping operation to prevent damage. Pin 11: This is the primary voltage detection pin, where the divided voltage from the primary winding is applied. If the voltage drops below 1V, the power supply turns off. Pin 12: Grounded pin, used as a reference point for other signals. Pin 13: This is the drive output terminal, connected to the gate of the switching transistor through a series resistor. It controls the switching action of the transistor. Pin 14: This pin connects to the power supply voltage and the start-up capacitor. During startup, the voltage is generated by the control winding of the transformer and then filtered and supplied back to the IC. Below is a summary of the DC voltages at each pin: 1: 2.8V – Ringing suppression and standby frequency 2: 1.6V – Primary winding current limit 3: 2.4V – Error adjustment and zero-crossing input 4: 3.0V – Soft start time and control speed 5: 3.7V – Optocoupler input 6: 0V – Fault comparator (V6 > 1.2V = stop) 7: 5.2V – RC oscillator or sync input 8: 0V – Unused 9: 5.2V – Reference voltage and current 10: 0V – Fault comparator (V10 > 1V = stop) 11: 3.2V – Primary voltage detection (V11 > 1V = stop) 12: 0V – Ground 13: 2.0V – Drive output 14: 12.0V – Supply voltage The TDA16846 is commonly used in TCL color TVs for switching power supplies. It features an independent oscillating circuit with options for fixed frequency, adjustable frequency, or synchronization. It also includes overcurrent and overvoltage protection, along with two voltage regulator inputs and two fault detection terminals. Starting Oscillation Principle: After the power switch is turned on, the AC voltage is rectified and filtered to produce around 300V DC. This voltage passes through the primary winding of the transformer and powers the internal circuit of the IC. A capacitor charges through a resistor, and once it reaches 16V, the IC starts oscillating, generating pulses to drive the switching transistor. The secondary winding provides feedback to maintain the IC’s power supply, while the 2-pin voltage is controlled to stay below 2.0V. Soft Start Circuit: To prevent damage during startup, the IC has a soft start circuit. The capacitor on pin 4 charges gradually, controlling the pulse width of the drive signal. This allows the switching transistor to turn on slowly, preventing sudden surges that could damage components. Troubleshooting Examples: [Example 1] A burnt smell and slight click sound were reported. Upon inspection, the +300V filter capacitor C809 was found cracked and replaced, resolving the issue. [Example 2] No power and no image were observed. After replacing the fuse and switch tube, the problem was traced to a faulty starting resistor, which was replaced, restoring normal function. [Example 3] A burned BUZ91 transistor was caused by an increased starting resistor value, leading to longer conduction time and excessive current. Replacing the resistor resolved the issue. [Example 4] A low voltage on pin 14 was due to a leaking capacitor, which was replaced, fixing the problem. [Example 5] A lack of line excitation was due to a faulty feedback capacitor, which was replaced to restore normal operation. [Example 6] Remote control issues were caused by a faulty capacitor on the CPU board, which was replaced to fix the problem. [Example 7] A black band on the screen was resolved by replacing diodes in the phase output stage. [Example 8] Grating size changes were due to a failed capacitor and diode, both of which were replaced to stabilize the display. [Example 9] Automatic standby failure was caused by a loose solder joint on a diode, which was re-soldered to resolve the issue. [Example 10] Intermittent power issues were due to a cold-state open circuit in a diode, which was repaired to restore functionality. [Example 11] Repeated triode failures were traced to a faulty diode, which was replaced to prevent further damage. [Example 12] Rear projection failures were caused by open resistors and a faulty IC, both of which were replaced to restore normal operation. [Example 13] No grating on startup was due to a damaged resistor on the CRT board, which was replaced to restore display. [Example 14] No startup was due to a broken CPU board, which was replaced to restore functionality. [Example 15] Boot issues were caused by a faulty DUY board, which was replaced to fix the problem. [Example 16] No grating was due to an open inductor, which was replaced to restore normal operation. [Example 17] No grating was caused by a faulty resistor, which was replaced to restore the sawtooth waveform and correct display. [Example 18] No color was due to a faulty crystal, which was replaced to restore normal video output. [Example 19] Button malfunction was due to a broken CPU board, which was replaced to restore control functionality. [Example 20] Grating compression was due to a faulty resistor affecting the sawtooth wave, which was replaced to restore normal display. [Example 21] No character display was due to a faulty capacitor, which was replaced to restore normal operation. [Example 22] No characters and vertical bars were caused by a faulty capacitor, which was replaced to restore normal display. [Example 23] Three-no issue was due to a faulty IC in the secondary boot circuit, which was replaced to restore power. [Example 24] No startup was due to a faulty diode, which was replaced to restore power and functionality. [Example 25] Burnt tube was due to a faulty capacitor, which was replaced to prevent further damage. [Example 26] Three-no issue was due to a saturated transistor, which was replaced to restore normal operation. [Example 27] Black screen was due to a faulty IC, which was replaced to restore display. [Example 28] Three-no issue was due to an open protection resistor, which was replaced to restore power. [Example 29] Line synchronization issues were due to a faulty capacitor, which was replaced to restore normal operation. [Example 30] Pincushion distortion and line jitter were due to a faulty component, which was replaced to restore normal display. [Example 31] Field compression was due to a faulty resistor, which was replaced to restore normal field operation. [Example 32] Black screen was due to a faulty resistor, which was replaced to restore normal operation. [Example 33] Black screen was due to a shorted IC, which was replaced to restore display. [Example 34] Pincushion distortion was due to an open resistor, which was replaced to restore normal display. [Example 35] AV/TV no picture was due to an open base bias resistor, which was replaced to restore signal processing. [Example 36] Repeated triode burning was due to a faulty diode, which was replaced to prevent further damage. [Example 37] Light flash and no power were due to a shorted load, which was replaced to restore normal operation. Zgar International (M) SDN BHD , https://www.zgarvape.com