Driving 12-30V Enable Signal to Flashing Lantern from Logic Level

Thread Starter

peckett

Joined May 9, 2021
9
Hello,

I am trying to build a flasher unit that is powered from 9-30V.
The lanterns are also powered from the same 9-30V and are turned on by an enable signal that must be 11V+.
I have opted to use a 12V buck boost converter to provide a steady 12V to drive the enable output.
I have also added an alternative circuit using a 5V LDO which then powers a 12V boost converter (not sure if this is a normal way of doing things).
I have been looking at ways to drive the enable pin with MOSFETS and optocouplers and all the circuits I see have resistors involved on the outputs so when I add the load (the lantern) it drops the voltage below 11V and the lantern will no longer turn on.
I am using a 555 timer that has a frequency range between 0.5 and 2Hz.
The circuit must also drive two lanterns alternatively.
I had a few ideas on how to drive the enable pin but not sure which one to go for and if they are best practices.

1) Power the 555 timer from 12V and drive the lantern enable pin directly from the timer and use a P channel MOSFETas an analog switch to invert the signal and driver the alternate lantern.
2) Power the 555 timer from 5V and use an optocoupler that switched 12V. I have built a circuit this way and it works but I am unsure of its best design practice as the collector is tied to 12V and the emitter is going directly to the output? if I add a pull up resistor and the enable output to the collector and tie the emitter to ground then the lantern loads the output and drops the voltage below 11V.

Any other thoughts or recommendations on best way to do this would be amazing.

I have attached my schematic to this thread.

Thanks
 

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crutschow

Joined Mar 14, 2008
27,395
Since the current required by the enable pin is low, you could likely use a 555 capacitive pump circuit to generate the higher voltage.

What is the maximum voltage the enable pin can tolerate, and what is its input impedance.?

Below is the LTspice simulation of a simple 555 voltage (near) doubler circuit.
The LM317 regulates the circuit voltage to about 7V from the 9V-30V input.
This gives an output of approximately 12V.

1620628350037.png
 

Thread Starter

peckett

Joined May 9, 2021
9
Hi crutschow, thanks for the reply
the input impedance of the lantern is 1k5 and can tolerate a voltage between 11-30V
Ah yes, I think I saw this somewhere before that could be perfect and save a lot of cost on components.
I just replicated your circuit there and it seems that the output is a stiff 12V and not alternating with the output of the 555.
I also need a 50% duty cycle so have used the LMC555 with cmos transistors and built the circuit with the charge pump circuit added but still not getting the desired switching voltage between 12 and 0V.
This may be down to component values but so will keep trying things out.
It looks like the voltage is switching at 12v after D1 but not at the out?

Thanks
 

Thread Starter

peckett

Joined May 9, 2021
9
OK so I am now switching 12V using a P MOSFET as an analog switch connected to the stiff output voltage from the capacitor charge pump.
I am switching at a very low frequency though so the capacitors discharge very quickly, there could also be up to 4 lanterns on the load as well so I am not sure if this way is possible unless I have huge capacitors on the pump circuit.
 

LowQCab

Joined Nov 6, 2012
732
It would seem that you are really making this far more complex than it needs to be.
It is not clear in your Schematics, or your explanation,
what your Power-Supply consists of, and how much Current your Flashing Lights draw.
Do you have an adequate ~25-Volt Supply ?
Is this Battery, or AC Powered ?
Do you have a single Flashing-Light, or 2-Alternating-Lights ?
.
.
.
LED Flasher FLAT .png
 

Thread Starter

peckett

Joined May 9, 2021
9
Sorry, the power could be coming from a 12V battery charged through a solar panel or a 24VDC PSU which is why it needs to work between 9-24V if the battery is low.
There will be 2-4 alternating flashing lights that draw about 150mA each when turned on.
The schematic I just threw together with a few ideas adding a buck boost converter to generate 12V regardless the source of the power.
The trigger input of the lantern could work with the change of a resistor value but unfortunately we have some already out in the field and they only turn on at about 11V annoyingly or could just use the battery voltage for the whole circuit.
I added a microchip to the schematic as further down the line may want to communicate with another controller to control the lanterns remotely but that isn't my concern for now was planning to have a basic build with the 555 timer or possibly using an op amp like you have done, then an advanced build.

Thanks for your help :)
 
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