schottky diode help (12VDC)

Thread Starter

itolond

Joined Feb 27, 2010
23
Hi Forum,

looking for help with rectifier (schottky) diode setup for a 12-14VDC automotive setup.

scenario
4 door with earth trigger switch. have a passenger side and drivers side courtesy light which should operate independently (e.g. when either passenger door opens the light is triggered (ground side of 12vdc LED light completes the circuit) as the same for the Driver side (all good so far). The challenge is all doors need to be connected to the input trigger for an alarm system which when open and armed will set off the siren. This requires both of the 'set' of door triggers to be combined to one single wire to the alarm and by doing so will have all courtesy lights illuminate regardless of door open.

Question:
will 2 x rectifier (schottky) diode isolate and allow the lights to work as well as the alarm trigger?
And if so what orientation is needed (see diagram)
 

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ericgibbs

Joined Jan 29, 2010
9,320
hi ito,
Please add the switches to your diagram.
What you are trying to do sounds feasible, but we need to see the rest of the circuit layout.
E
 

crutschow

Joined Mar 14, 2008
24,077
The diodes need to be reversed with a resistor in series going to the +12V.
The resistor-diode junction will then go to near ground when a door opens.

If you need a high voltage when a door opens, then you could add a transistor inverter.
 

Thread Starter

itolond

Joined Feb 27, 2010
23
hi ito,
Please add the switches to your diagram.
What you are trying to do sounds feasible, but we need to see the rest of the circuit layout.
E
The door tiggers are simple on/off switches - when the door opens a spring tensioned plunger creates a circuit to chassis ground. no other switches are involved as the alarm simply looks for the trigger (to ground)
 

Thread Starter

itolond

Joined Feb 27, 2010
23
The diodes need to be reversed with a resistor in series going to the +12V.
The resistor-diode junction will then go to near ground when a door opens.

If you need a high voltage when a door opens, then you could add a transistor inverter.
A. both diodes should face the opposite of what they show on the diagram now?
B. where exactly should the resistor be installed - wouldn't the LED light provide some level of resistance (soory I am not sure I follow the resistor purpose
 

crutschow

Joined Mar 14, 2008
24,077
our circuit looks OK to me.
You added a switch.
The TS stated there are no other switches.
He wants to detect when any door switch is closed.
A. both diodes should face the opposite of what they show on the diagram now?
Yes.
B. where exactly should the resistor be installed
From the bottom junction (now the anodes) of the diodes to +12V.
wouldn't the LED light provide some level of resistance (soory I am not sure I follow the resistor purpose
Yes, the LEDs provide resistance but not where you need it.
The resistor is to provide 12V at the diode-resistor junction (for your alarm) when all switches are open, and near ground voltage (1 diode drop) when a switch is closed.
 

ericgibbs

Joined Jan 29, 2010
9,320
This requires both of the 'set' of door triggers to be combined to one single wire to the alarm and by doing so will have all courtesy lights illuminate regardless of door open.
The door tiggers are simple on/off switches - when the door opens a spring tensioned plunger creates a circuit to chassis ground. no other switches are involved as the alarm simply looks for the trigger (to ground)
hi,
The way I read the post is that he wishes to combine all the lights to be ON when then the Alarm is activated.?? ie:

Perhaps the TS will clarify.

E
 

Thread Starter

itolond

Joined Feb 27, 2010
23
"The way I read the post is that he wishes to combine all the lights to be ON when then the Alarm is activated"

No - the Alarm simply 'looks' for a trigger, in that when a Door is opened and the vehicle is armed (authorized entry) it will set off the alarm.

The LED lights (passenger or driver) should illuminate when the doors are open by completing the circuit to ground for the LED
 

ericgibbs

Joined Jan 29, 2010
9,320
"The way I read the post is that he wishes to combine all the lights to be ON when then the Alarm is activated"
No - the Alarm simply 'looks' for a trigger, in that when a Door is opened and the vehicle is armed (authorized entry) it will set off the alarm.
hi,
That makes a difference.
So is the Alarm expecting a Low going trigger.??

If Yes, then the circuit is incorrect.
E


Update:

Check this option.
 

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