Switching regulator circuit diagram based on uA78S40

The uA78S40 is a switching regulator IC that can be used in a variety of applications. The uA78S40 is an integrated switching regulator circuit with a built-in reference voltage source circuit with temperature compensation, an oscillator with duty cycle control, a high-capacity switching element, an independent operational amplifier, and an independent diode. When a voltage exceeding 40V or an output current exceeding 1.5A is required, an external switching transistor must be used. Features of the uA78S40 include a wide temperature range, adjustable output voltage (from 1.5V to 40V), a peak output current of 1.5A, 80dB load regulation, 80dB line regulation, a wide supply voltage range (from 2.5V to 40V), very low standby current, etc. Applications of this IC include boost converters, buck converters, inverting converters, etc. The uA78S40 is packaged in a 16-pin DIP plastic package.

Buck converter circuit based on uA78S40

The circuit shown in the figure above is a switching buck converter using uA78S40. The input voltage can be 25VDC and the output voltage can be 5V@500mA. Ct is the timing capacitor of the internal oscillator, while C3 is the input filter capacitor. The rated voltage of C3 must be higher than 25V, while the rated voltage of C2 must be higher than 10V. The instantaneous output voltage (i.e., the voltage across the output capacitor Cc) is fed back to the inverting input of the internal operational amplifier using a resistor network composed of R1 and R2. R2 and R1 can be used to set the output voltage. Using an external rectifier diode D1 can improve the overall efficiency of the circuit. If it is necessary to use the internal diode of the IC instead of D1, omit D1 and restore the track shown by the dotted line.

Inverting converter circuit based on uA78S40

An inverting converter is a circuit that reverses the polarity of a given input voltage. For example, if 5VDC is applied at the input of the inverting converter, the output voltage will be -5VDC. As shown above, a 40V inverting converter circuit using the uA15S78 is shown. Ct (in circuit C1) is the timing capacitor for the IC's internal oscillator, C3 is the input filter capacitor, and C2 is the output filter capacitor. The voltage rating of C2 and C3 must be at least 25V. Resistors R1 and R2 form a feedback network that feeds back part of the output voltage to the non-inverting input of the Ics internal comparator. R2 and R1 can be used to set the output voltage. Transistor Q1 is the external switching transistor. The collector terminals of the internal driver and switching transistors are shorted and connected to the base of the external switching transistor through resistor R3.