I have this circuit, where i wish to turn lower one to ON after a delay, so that at one time only one of them is ON. The input wave is a PWM Square Wave. Can anyone suggest how i can do so?
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\$\begingroup\$ I'm guessing here but don't you also want to delay the time the top MOSFET starts conducting too. Circuit would solve this and an application description. \$\endgroup\$– Andy akaCommented Sep 15, 2013 at 10:10
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1 Answer
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Use a simple AND gate and an RC delay.
When the input edge goes from 0 to 1 the capacitor input B goes HIGH immediately but C1 holds the A input LOW and starts to charge through R1. With B HIGH and A LOW the output, Q, is LOW. As the capacitor charges through R1 it eventually reaches a voltage level (50%) when the A input is seen as HIGH and the gate out switches HIGH. This takes Td = 0.7C1R1 (C in Farads, R1 in Ohms, Td in Seconds) approx. and produces a TURN ON delay at the leading edge.
When the input goes LOW the output of the gate follows it (after a small gate delay time) and goes LOW, even though the capacitor is now charged and holding the A input HIGH. The LOW input allows the capacitor to discharge through R1 and it eventually goes LOW ready to start again.
If a faster discharge time is required a diode could be connected across R1 but this would not change the logic.
