The switching regulator in Figure 1, which converts 5V to 12V, is a simple and low-cost alternative to special-purpose, power regulator ICs. The circuit uses a TTL hex inverter in an unusual manner to provide all the functions necessary for a dc/dc converter. These functions include the oscillator, power switch, and error amplifier.

The circuit relies on TTL-switching thresholds to regulate the output voltage. Even though this circuit doesn't provide the best reference voltage, the circuit produces surprisingly good results. The measured line and load regulation are better than 1%, and temperature testing from 0 to 508C increases output voltage variation only by 7%. Applications that don't require extreme accuracy for an auxiliary voltage would benefit from this simple and very cost-effective solution. The total circuit costs <$0.30, including a 10-cent "switching-regulator controller." Applications include auxiliary bias voltage for powering op amps, comparators, and MOSFET high-side drivers.

IC_1A and IC_1B form an easy to recognize oscillator circuit; the design sets the switching frequency to <1 MHz. The output of the oscillator drives the parallel inverters IC_1C, IC_1D, and IC_1E. Paralleling the outputs allows higher switching currents and, thus, more output power. Internal output transistors serve as a main power switch, which forms a standard boost converter with L₁ and D₁. During the output low state, the bottom side of L₁ effectively connects to ground, and the current ramps up in the inductor. When the output switches high, energy stored in the inductor forces the voltage at D₁'s anode to fly high, and D₁ starts conducting, charging output capacitor C₁.

The voltage across C₁ rises to 12V, and IC_1F performs the regulation. The input of IC_1F monitors the output voltage using feedback resistors R₁ and R₂. When the output increase forces IC_1F's input above the TTL-logic threshold (around 1.2V), IC_1F's output switches low, disabling the output stage. When the output voltage drops below 12V, IC_1F switches off, allowing the oscillator to drive the power switch.

The 12V-output requirement mandates the use of the 7406, which is an open-collector hex inverter with a 30V output-breakdown voltage. This inverter safely produces produce voltages as high as 24V. Output collector current is recommended not to exceed 40 mA, so with three buffers in parallel, 120 mA of switching current is available.

The circuit's high frequency of operation allows the use of a tiny chip inductor; multiple manufacturers offer chip inductors in a variety of surface-mount sizes. Ceramic capacitors, which provide the input and output filtering, are more available than tantalum and more reliable than their aluminum electrolytic counterparts. Input current is approximately 120 mA. (DI #1870)