The TL494 is a common integrated circuit used for switching power supply control. It provides a stable method of regulating the output voltage and current of a power supply to the desired specifications. The chip has a wide range of applications, including transformer drivers, power adapters, and AC to DC converters.
The TL494 typically operates in switching mode. In this mode, the power supply is switched at a very high frequency, such as a few tens of kHz or more, converting the power flow into pulses, which are then passed through a filter circuit to provide a stable DC output. This approach is more efficient than a conventional linear regulator because it reduces wasted energy. The operating principle of the TL494 switching power supply is described in detail below.
Reference Voltage Source: The TL494 chip has an internal reference voltage source which generates an accurate reference voltage. This voltage is usually 5V and is used to compare with the feedback circuit to regulate the output voltage. The reference voltage can be adapted to different power supply requirements by choosing the right external components.
Error Amplifier: The TL494 also contains an error amplifier, which is the core component that enables closed-loop feedback control. It works by comparing the reference voltage to the feedback signal and amplifying the difference to an appropriate level. The output of this amplifier is connected to a PWM (Pulse Width Modulation) controller.
PWM Controller: The PWM controller receives the output of the error amplifier and generates a PWM signal based on it.The frequency of the PWM signal is determined by an external component, while the modulation ratio is adjusted according to the output of the error amplifier. The modulation ratio represents the proportion of time between high and low levels in the PWM signal. This ratio controls the on-off time of the switching tubes, and thus the stability of the power supply output.
Switching Driver: The PWM signal is passed through the switching driver to the switching tube. The switching tube acts as a switching power supply, conducting at high levels and truncating at low levels. In this way, the power supply in switching mode starts to operate, converting the current into a pulsed signal.
TRANSFORMER: The switching tube is connected to the main coil of the transformer, which converts the input voltage into a suitable output voltage through the transforming action. The auxiliary coil in the transformer generates a negative feedback signal to control the accuracy of the output voltage. This feedback signal is sent back to the error amplifier to form a closed loop feedback system.
OUTPUT FILTER: The output filter circuit is used to extract the desired stable DC output from the pulsed signal. It includes components such as inductors, capacitors, and resistors to smooth out and filter the pulsed signal. In this way, the output power supply can provide stable voltage and current for various electrical devices.
With the TL494 chip, the switching power supply can provide stable output voltage and current according to different input voltages and load demands. It can dynamically adjust the modulation ratio according to the difference between the reference voltage and the feedback signal to control the on-off time of the switching tubes. Due to the efficient switching mode operation principle, the TL494 switching power supply offers higher efficiency and more flexible applications than traditional linear regulators.
To summarize, the operating principle of the TL494 switching power supply can be briefly summarized as follows: a reference voltage source generates a reference voltage, an error amplifier compares the reference voltage with the feedback signal, a PWM controller generates a PWM signal, a switching driver passes the PWM signal to the switching tubes, a transformer converts the input voltage to an appropriate output voltage, and an output filter circuit extracts and smoothes the output voltage. This principle of operation allows the TL494 to achieve efficient and stable switching power supply control.
