Build a simple complementary-bracket-pulse generator

When building push-pull switching power converters or motor controllers, you often need alternating pulses with a small amount of dead time between them to minimize simultaneous conduction in output-switching devices. Switching controller ICs have this feature, but they usually operate within closed loops to minimize IC pin count. When optimizing switching output stages, you may need open-loop control. Figure 1 shows how you can build such a generator with just two common ICs. As a bonus, both the overlapping, P-channel drive and the nonoverlapping, N-channel drive are available simultaneously.

The circuit’s input, Pin 10 of IC₁, comes from clock generator IC_2F. A slightly delayed and inverted version occurs at IC₁’s Pin 9 from IC_2A. IC₁ then decodes the original and delayed inputs to form the desired outputs (Table 1). Because IC₁ is an analog demultiplexer, you can set its outputs either active high or active low with pull-up or pull-down resistors. You determine the high or low inactive state by tying the X or Y pins to either the power-supply voltage or ground. Depending on the state of IC_1A’s A and B inputs, internal switches in IC₁ close between X and X0 to X and X3, as well as from Y and Y0 to Y and Y3. Buffers IC_2B through IC_2E buffer and invert the resulting outputs. You can use the remaining gate as a variable-frequency or variable-duty-cycle generator. You determine the dead time, which is independent of frequency or duty cycle, using the time constant of R₁ and C₁. Depending on output-device characteristics and switching frequency, output buffers may require an additional stage, or you can replace them with MOSFET-gate-driver devices. Supply voltage is not critical but should be high enough to guarantee that output devices fully turn on. In general, a higher supply voltage allows for higher-speed operation. The MC14xxx series of ICs is the same as the CD4xxx series. If you need higher-frequency operation at lower supply voltages, then use the 74HC4xxx-series devices. All of these ICs are available from a number of manufacturers, including Texas Instruments (Reference 1) and On Semiconductor (Reference 2).

Click here for the illustrations:

Figure 1, Table 1

Caption
Figure 1: You can build a simple pulse generator with just two commonly available ICs.
References
1. “CD4051B, CD4052B, CD4053B,” Texas Instruments, October 2003.
2. “Semiconductor and Integrated Circuit Devices,” On Semiconductor.