Knowing the division of labor of each pin of TL494 will definitely not be difficult for you in practical application

TL494 is a voltage-driven pulse width modulator produced by TI. It can be used as a switching power supply circuit in monitors, computers and other systems. The output transistor of TL494 can be connected in two ways: emitter and emitter follower. You can choose double-ended push-pull output or single-ended output. If used in push-pull output, the two drive pulses differ by 180 degrees, while in single-ended output, the two drive pulses are of the same frequency and phase.

Functions and features of TL494

The TL494 functional block diagram is shown in Figure 1, and the pin functions are as follows:

Pin 1 is the non-inverting input of the error comparator amplifier.

Pin 2 is the inverting input of the error comparator amplifier.

Pin 3 is the common output terminal of the control comparator amplifier and the error comparator amplifier. When outputting, it shows the output control characteristic, that is, in the two amplifiers, the one with the larger output amplitude works. When the level of pin 3 becomes high, the width of the driving pulse sent by TL494 becomes narrower, and when the level of pin 3 is low, the width of the driving pulse becomes wider.

Pin 4 is the dead zone level control terminal. Adding the dead zone control voltage from pin 4 can control the maximum width of the drive pulse so that it does not exceed 180 degrees, thereby protecting the transistors in the switching power supply circuit.

Pin 5 is used to connect an external oscillator resistor .

Pin 6 is used to connect an external oscillation capacitor .

Pin 7 is the ground terminal.

Pins 8 and 9 are the collectors of the two output transistors at the final stage of TL494.

Pins 11 and 10 are the emitters of the two output transistors at the final stage of TL494.

Pin 12 is the power supply terminal.

Pin 13 is the function control terminal.

Pin 14 is the internal 5V reference voltage output terminal.

Pin 15 is the inverting input terminal of the control comparator amplifier.

Pin 16 is the in-phase input terminal of the control comparator amplifier. Application of TL494 in the circuit

Figure 2 is a computer switching power supply circuit composed of TL494 (only the pulse width control oscillation circuit is drawn). The TL494 in the figure works in push-pull output mode and is connected in common emitter form. The pulse signal T2 output from pins 8 and 11 is coupled to the main switch transistors VT1 and VT2, which can put them in an oscillating state.

As can be seen from Figure 3, the emitter follower form adopts the push-pull output method. The pulse output from pins 9 and 10 is first input to pins 12, 8 and 2, 6 of the NE556 circuit, and finally the pulse signal is output from pins 5 and 9 of the NE556 circuit to drive the two C MOS field effect transistors VT1 and VT2, so that the entire circuit can proceed smoothly.