Cmos circuit is automatically switched on when applying power

Thread Starter

Holz1

Joined Jan 21, 2020
30
Hello friends
When I apply power to a cmos circuit f.i. the IC 40106 Hex inverter, the circuits starts. It is more ore less logical that the circuits starts because the power is + 5 volts (signal high) and because the inverter inverts the power into -5 Volts (signal low).
I have tried to connect pull-up and pull-down resistors but that didnot function.
Is there a simple solution to prevent starting circuits automatically when applying power.
 

Thread Starter

Holz1

Joined Jan 21, 2020
30
I have read something about an mosfet that can prevent switching on, but I don't know if this is correct. Massive info but I am not able to see the solution for the problem
 

eetech00

Joined Jun 8, 2013
3,823
Hello friends
When I apply power to a cmos circuit f.i. the IC 40106 Hex inverter, the circuits starts. It is more ore less logical that the circuits starts because the power is + 5 volts (signal high) and because the inverter inverts the power into -5 Volts (signal low).
I have tried to connect pull-up and pull-down resistors but that didnot function.
Is there a simple solution to prevent starting circuits automatically when applying power.
Post the schematic circuit that shows use of the hex inverter.
 

LesJones

Joined Jan 8, 2017
4,172
You are confusing the quesion by saying thet the problem is with a 40106 IC.
Are you saying that the first schematic in post #4 always powers on in the on condition even when the auto action is set to the off position ?

Les.
 

Thread Starter

Holz1

Joined Jan 21, 2020
30
I said " take for instance (f.i) the cd40106". I use a transformer 20 V DC and output 5 volt dc.
I like to prevent that my circuits starts automatically when the power to the circuit is switched on.
I think this is not a problem to solve for an electrician, which I am not!
when I connect cd 40106 : When the power supply connected this gives a high signal (+5 volts) and inverted gives a low signal.
(https://www.allaboutcircuits.com/textbook/digital/chpt-3/digital-signals-gates/ )
( I think this is for everybody clear what I mean!)
My request: connect powersupply to circuit-> circuit remains off.
I found a possible solution (see the pdf attached in which is specified the use of MOSFETS .
 

Papabravo

Joined Feb 24, 2006
21,003
Can a buffer-gate stop the power-on when I connect the power to the circuit?

https://www.allaboutcircuits.com/textbook/digital/chpt-3/buffer-gate/
No. Do not confuse the output state of a given gate with the power being on or off. Just because the output of a gate is at or near ground does not mean that the power is blocked. When you connect power to a circuit there will be a set of transient behaviors which are not characterized or guaranteed. Once the power rails reach a stable value, circuits will then behave according to their specifications listed in the datasheet. In most complex systems there is, by design, a reset procedure which ensures that all devices begin operation in a known state. It is also common to include circuitry that detects undesirable states and transitions to a known state.
 
Last edited:

crutschow

Joined Mar 14, 2008
34,047
Your problem, as stated, is unclear.
What do you want the circuit to do when the power is applied, and when do you want the circuit start to operate normally?
 

eetech00

Joined Jun 8, 2013
3,823
I like to prevent that my circuits starts automatically when the power to the circuit is switched on.
Until you show the circuit you want to modify, you may be over complicating the circuit.
It may only need a simple POR circuit, and the circuit you've attached may not even be needed.
 

AnalogKid

Joined Aug 1, 2013
10,944
I like to prevent that my circuits starts automatically when the power to the circuit is switched on.
Then what will "make it start"?

It sounds like you want the output of a logic gate to be inhibited on power-up, but then function normally later on. If this is what you are asking about, then, as has been said, the answer depends on the specific details of the logic circuit. There is no single solution for all circuits.

If you are talking about applying power to a system, but power is not sent out to all parts of the system until a button is pressed, like an ON button, that is a very different question. In that case, an "On/Standby" switch could do what you want. Again, depending on the system there are many ways to do this. Most of them are variations of a toggle flipflop, with one component beefed up to handle the power. The circuits you attached will do this. As above, the details of the circuit must be adjusted to fit the operating parameters of your system.

ak
 

drjohsmith

Joined Dec 13, 2021
850
You could meet the requirement of the circuit not powering on when power is applied,
by fitting a zero ohm resistor between the power supplies and ground
might not be what you want but it fits the requirements as given so far,
please mark this as liked if you agree this meets your requirements ,
 

MisterBill2

Joined Jan 23, 2018
17,814
I have read something about an mosfet that can prevent switching on, but I don't know if this is correct. Massive info but I am not able to see the solution for the problem
Hello friends
When I apply power to a cmos circuit f.i. the IC 40106 Hex inverter, the circuits starts. It is more ore less logical that the circuits starts because the power is + 5 volts (signal high) and because the inverter inverts the power into -5 Volts (signal low).
I have tried to connect pull-up and pull-down resistors but that didnot function.
Is there a simple solution to prevent starting circuits automatically when applying power.
The CD40106 inverter must have an input to deliver an output that is predictable. It is totally useless to power the IC if there will not be an input. To have it output +5 volts reliably when it is powered there must be applied ZERO volts at each input. No other way to do it.
AND, by itself, the CD40106 hex inverter is rather useless except as a spare part. Combined with other parts in a circuit, it van be very useful and quite handy.
So we need a description of a circuit, or an actual circuit schematic drawing, to offer any useful advice.
 

Thread Starter

Holz1

Joined Jan 21, 2020
30
The POR (power on reset) is the solution.
Oké let me explain: I have 2 separate infrared gates along my modelrailway track: the first IR gate triggers the circuit in ON and when passing the 2nd IR gate the circuit will be switch OFF.

the IRgates give the output LOW when paasing the IR gate. (I could build the IR gates also as HIGH but this is my choice).
By using the CD40106, the inputsignal LOW is inverted into HIGH and is further passed to another IC.
Now when applying power to the circuit there shouldnot be sent a pulse which triggers the IC in the rest of the application which it does now. So the POR is I think i will investigate
 

LesJones

Joined Jan 8, 2017
4,172
You are making it very difficult for people to help with your problem as you will not supply a schematic. From the very limitied information you have just supplied it seems that you need to hold the "trigger IC" (Which I guess may be a 4013.) in a reset condition for a few mS when power is applied. Without a schematic we can't suggest how to do that.

Les.
 

BobTPH

Joined Jun 5, 2013
8,664
What you have described is a circuit that has bo power switch, so when you power it up it starts operating, right?

So the solution is to add a power switch between the power supply + and the circuit +.
 
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