Hi! Simple dumb question that I can not scratch my brain right now.
I have built this simple momentary switch latch circuit, intentions are to use it with a relay and turn on / off an amp with a push button. Works as intended, only problem is , when the circuit is powered, it starts in the on position. How can I modify it so when power is applied it stays off until I press the button.
- Bruno.
I have built this simple momentary switch latch circuit, intentions are to use it with a relay and turn on / off an amp with a push button. Works as intended, only problem is , when the circuit is powered, it starts in the on position. How can I modify it so when power is applied it stays off until I press the button.
- Bruno.
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All you need is two momentary switches, and a latching type relay that has a coil for your AC line voltage,
and contacts rated for the amplifier input current.
You push the momentary switch #1 to turn the amp on, and push #2 switch to turn it off.
https://www.electrical4u.com/latching-relay/
and contacts rated for the amplifier input current.
You push the momentary switch #1 to turn the amp on, and push #2 switch to turn it off.
https://www.electrical4u.com/latching-relay/
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Yes. Observe electrolytic capacitor polarity. I have not simulated this so there may be complications, but it should be fine. I see that the circuit depends on a load for pull-down. Perhaps if the capacitor was on the other side of the latch, a ground reference would also work, ie switch to the P-channel gate. I would avoid exotic parts like the dual MOSFET and use common parts like FPQ27P06 and 2n7002.
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@MarcelvdG Load was A led with a 330ohm resistor at about 30mA , maybe that was the problem. ( using the 10k resistor as I mentioned yesterday made it work only that if the load was bigger it would " die " and stay off until I would press the button again, that wouldn't happen when using the first schematic. I should test with the relay coil as load, Also with the cap in the position @steveu mentioned.
Attached are some "high voltage" versions. These will not work with 5 Volts. Note that using a P-channel MOSFET as the switch is not a great idea because they always have a higher on resistance, so included is an inverted version using a N-channel MOSFET and a PNP instead of a P-channel MOSFET because they are more common and cheap. The voltage losses of the N-channel MOSFET here are about 0.01V for 2 Amps instead of 0.1V for the P-channel switch. Note that the raw DC has to be floating, ie not grounded.
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The circuit only works with a suitably heavy load - you could try changing the 100k to 1M, and reducing the 1µF cap to 100nF, that should make it less likely to trigger on power up.
Note that simulating these in LT Spice requires the option to start external voltages at 0V, in the transient dialog, otherwise it pre-charges caps and you don't get the correct results.