TL494 PWM Controller - Circuit Design TL494 micro chip is a PWN controller used in pulse power supply unit. The controller includes an error amplifier, comparer, control trigger, regulator, output stage control circuit and built-in adjustable generator. The micro chip operates at the fixed frequency determined by the internal generator. Autonomous output drivers ensure the output stage operation according to the common emitter circuit design or emitter follower circuit design. TL494 output operates in a single shot or multi shot modes. You can switch the mode using a special input. The controller's output stage is a transistor with an opened emitter and collector. That's why you can connect this transistor according to two connection options -- common emitter connection or common collector connection. If the reference voltage is applied to the mode switch input, the trigger directly controls two output resistors in phase opposition. The output frequency will be equal to the half-frequency of the generator. The single shot mode requires high current, output transistors can support parallel operation. For this purpose, you need to ground the mode switch input. This will block the output signal from the trigger. PWN controller regulator performance depends on the amplitude frequency characteristic of its error amplifier. The error amplifier outputs have a high active voltage level. They have a common OR function at the PWN comparer input. The discharge of a capacitor at the comparer's output generates a positive impulse that clocks the trigger and blocks output transistors. TL494 has a built-in reference voltage source of 5 Volts. This ensures drain current of up to 10 mA used to shift external circuit components.