Design Considerations of An Switching Regulator

An oscilloscope is required when building a switching regulator. When checking the oscillator ramp on pin 3 the oscilloscope may be difficult to synchronize. This is a normal operating characteristic of this regulator and is

Figure 6-33. Inverting Applications

caused by the asynchronous operation of the error amplifier to that of the oscillator. The oscilloscope may be synchronized by varying the input voltage or load current slightly from design nominals.

High frequency circuit layout techniques are imperative. Keep leads as short as possible and use a single ground point. Resistors Rl and R2 should be as close as possible to Pin 1 to eliminate noise pick-up in the feedback loop. The TL497 A type of circuits do not need “hi-Q” inductors. They are, in fact, not desirable due to the broad frequency range of operation. If the “Q” is too high, ringing will occur. If this happens a shunt resistor (about 1 kΩ) may be placed across the coil to damp the oscillation.

While not necessary, it is highly desirable to use a toroidal inductor as opposed to a cylindrically wound coil. The toroidal type of winding helps to contain the flux closer to the core and in turn minimize radiation from the supply. All high current loops should be kept to a minimum length using copper connections that are as large as possible.