Ok to the issue I have been plagued with for some time now. The circuit is powered by a 4s Battery Pack (max VBAT = 16.8V, well below the CD4017 max V of 20V) After the Power-ON stage it is branched out to Voltage Regulators, see below.
I have designed (copied) a circuit using the (in)famous CD4017 decade counter as a pushbutton ON/OFF circuit.
- Hold pushbutton 3-4s decade counter switches from Q0 to Q1. This will power the MOSFET stage providing power to everything
- Hold pushbutton 3-4s decade counter switches from Q1 to Q2, which is tied into the Reset, which will reset it.
With the initial design I encountered some problems.
- Floating GND issue
- The reason I'm here. The CD4017 just resets itself, after just a very short ON pulse on Q1
Now you may wonder why n-channel to p-channel? I found the Voltage regulators tend to dislike a "floating" GND, which is the case, when switched by n-channel MOSFET. In the case of floating ground, these silly voltage regulators switch INCOMING directly to OUTPUT. (Yeah, don't ask me how I found out. Let's just say smoke was involved) <\For background information only>
Problem 2 (Actual reason I'm here) Now while the first problem also dealt with Power-ON issues, it was ultimately the floating ground prompting a re-design.
With Load attached (any one, or all Voltage regulators at same time) the CD4017 briefly switches Q1 HIGH, then resets itself. I have done the testing with only a single Voltage regulator connected and also with all three connected. Further downstream from the Voltage Regulators, there are no other loads during the testing, except of the status LEDs for each voltage.
Without any of the Voltage Regulators connected, the CD4017 switches happily between Q0 -> Q1 and then from Q1 -> Q2 (reset)
What have I tried so far?
- Due to inductive load, I have tried to add a freewheeling diode in multiple places, no luck
- disconnected capacitor C101 from the reset line, as I thought maybe the RST-spike comes from here. But later found the forum below explaining it is to deal with uncertain state on power-up, so I reconnected it.
- removed the load, powered on and then connected the load. Same issue.
I have searched the internet before posting and spend a good amount behind the oscilloscope to get an idea what is wrong, but seemingly I have hit my limits. More on the oscilloscope can be found below
This is one of the other posts I found, describing a similar problem, however in the end it did not help me. Power-on Reset for CD4017 gives unexpected results
Below are now some images, hopefully these will help. First is the schematic, followed by some oscilloscope traces.
Please, somebody with more in-depth understanding guide me into the right direction here. Been dealing with this for a month now :-/