Generating two independent pulse triggers separated by a certain time delay can be handy in half-bridge drivers and thyristor-commutated lamp flashers. Time delay is set to avoid overlapping of the power switches' ON states or to minimize the stress on the thyristor's gate. A simple implementation is shown in Figure 1.

Augmenting an earlier published design,^{1} the circuit for CMP1 is a free-running multivibrator whose period is found by T = 1.39R1C. Voltage across C (V_{C}) alternately charges and discharges between V_{CC}/3 and 2V_{CC}/3. Whenever V_{C} exceeds R3V_{CC}/(R2 + R3), CMP2's output (Q1) goes low while CMP3's output (Q2) is high. Similarly, whenever V_{C} falls below R4V_{CC}/(R4 + R5), Q2 goes low while Q1 is high. Then when V_{C} is found between these two trip points, both Q1 and Q2 are low.

Figure 2 shows the circuit's timing signals. Letting k = R3/(R2 + R3) and m = R4/(R4 + R5), where 2/3 > k > m >1 /3, it can be shown by using the RC charge-discharge equations^{2} that the pulse widths and time delays are:

t_{W1 }= R1C_{LN}\[2(1 − k)/k\]

t_{D1} = R1C_{LN}(k/m)

t_{W2} = R1C_{LN}\[2m/(1 − m)\]

t_{D2} = R1C_{LN}\[(1 − m)/(1 − k)\]

T = t_{W1 }+ t_{D1} + t_{W2} + t_{D2}

You will observe that V_{CC}, which in this case could be anywhere between 2 and 28 V, doesn't affect the timing characteristics. The three 1-kΩ resistors are for pull-ups.

References:

- Edang, Arthur E., "Independently Vary A Multivibrator's Duty Cycle and Frequency," electronic design, Oct. 28, 2002, p. 74.
- Franco, Sergio,
*Design with Operational Amplifiers and Analog Integrated Circuits 3e*. McGraw-Hill, 2002, p. 450.