The TL594 oscillator frequency is controlled by connecting an external timing circuit consisting of a capacitor and resistor to pins 5 and 6. The oscillator is set to operate at 20 kHz using the component values calculated by the following equations.
The error amplifier compares a sample of the 5 V output to a reference and adjusts the pulse-width modulator to maintain a constant output as shown in Figure 6-21.
The TL594’s internal 5 V reference (pin 14) is divided to 2.5 V by R3 and R4. The output voltage error signal is also divided to 2.5 V by R8 and R9. If the output must be regulated to exactly 5.0 V, a 10 kΩ potentiometer may be used in place of R8 to provide an adjustment control.
To increase the stability of the error amplifier circuit, the output of the error amplifier is fed back to the inverting input through R7, reducing the gain to 100.