Power up delay

154

02:03:02

Start the circuit by pressing the switch on the left.
The transistor next to the capacitor causes a fast discharge of the capacitor when power is switched off, so the circuit is ready again very fast.

published 9 years ago

DWLF

9 years ago

Add another relay and this circuit can be of great use. One example would be to add a relay that as soon as the switch is on, it powers a heater to warm up a device that will then power on after it's a little warmed up. Adjust the capacitor to choose the delay before power on. Or maybe have this circuit that when switched on it will activate a heater to dry a moist circuit or motor before power on such as from condensation outside.

ManuelPeh

9 years ago

An easy way to get it work like that: building the circuit two times. The second one receives its power from the relais of the first one. It starts to load the cap when the first stage has switched on.

cue108

9 years ago

Why would one need a power up delay like this? The op-amp makes sure that the switch on moment is very short over the relais driver transistor. Power up delay in conjunction with inductive loads I only know with a controlled ampere increase time to reduce the stress on the power supply for example.

ManuelPeh

9 years ago

This kind of circuit is used in audio amps. It delays the connection from the last amp stage to the speakers. The amp needs some seconds to regulate its output to 0V. The delayed connection provides that the speakers wont be harmed.

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