12v circuit doubt with switching

Thread Starter

matrixpt

Joined May 24, 2021
7
Hello,

this is my first design and i would like to have if possible some help.

The feed is 12v, but i wish to limit minimum of 8v and maximum of 13.5v.... (1A max)

i know that myght have some other faults...

Can anyone help me.

amp_controler.jpg
thanks
 

AnalogKid

Joined Aug 1, 2013
9,494
It will take two comparators, a voltage reference (like a zener diode), plus some resistors to create a window comparator, but it is not a complex circuit. But first, let's clarify your question ...

1. Please repost the schematic with reference designators for the two switches.

2. Are you saying you want to limit the voltage going to the LEDs to a max of 13.5 V and a min of 8.5 V?

3. Do the LEDs have built-in current limiting?

4. To assure clean and fast turn-off of Q1 and Q2, add a 10K resistor from the base of each transistor to GND.

5. What is the purpose of C1?

ak
 

Thread Starter

matrixpt

Joined May 24, 2021
7
1. Please repost the schematic with reference designators for the two switches.
the switches are only to choose between if i want one or another, regular on/off ones.

2. Are you saying you want to limit the voltage going to the LEDs to a max of 13.5 V and a min of 8.5 V?
yes

3. Do the LEDs have built-in current limiting?
yes,


5. What is the purpose of C1?
i need a small delay...

df
 

dl324

Joined Mar 30, 2015
13,527
What is the purpose of D1-3?

If you want to limit the voltage to both LEDs to be 8.5-13V, what will do that for D22?

Why are you using a power transistor for Q1 and rectifier diodes for D1-D3?

Your schematic drawn more conventionally:
1634401853681.png
What do you think is limiting the LED voltage to your desired range?
 

AnalogKid

Joined Aug 1, 2013
9,494
Is it possible for V1 to go above 13.5 V? If so, this complicates the circuit because now it has to turn off the LED(s) even when switches are preased.

Also ...
1. Please repost the schematic with reference designators for the two switches.
the switches are only to choose between if i want one or another, regular on/off ones.
I'm not asking for the switch type or part number. You should assign a unique reference designator to each switch (SW1, SW2, etc.) so they can be discussed without errors. If I say "When you press the switch ...", how do you know which switch I am referring to?

ak
 

Thread Starter

matrixpt

Joined May 24, 2021
7
If you want to limit the voltage to both LEDs to be 8.5-13V, what will do that for D22?
the idea is to have that safety for both D17 And D22 individualy!

Why are you using a power transistor for Q1 and rectifier diodes for D1-D3?
My first schemmatic, so trying to learn..

What do you think is limiting the LED voltage to your desired range?
both D17 and D22 if i feed them with more than 13.5v they blown.

Is it possible for V1 to go above 13.5 V? If so, this complicates the circuit because now it has to turn off the LED(s) even when switches are preased.
yes

I'm not asking for the switch type or part number. You should assign a unique reference designator to each switch (SW1, SW2, etc.) so they can be discussed without errors. If I say "When you press the switch ...", how do you know which switch I am referring to?
v2.jpg
 

dl324

Joined Mar 30, 2015
13,527
My first schemmatic, so trying to learn..
Schematics should flow primarily from left to right and top to bottom. We avoid unnecessary wire jogs and try to align components.
both D17 and D22 if i feed them with more than 13.5v they blown.
What are the LED specifications?

Why is the meter on D22 reading 0.66V when SW2 is opened? Do the blue squares denote nets at 0V?

Since you want to limit the voltage to the LEDs, that implies that the input voltage can change. Why don't you just regulate the input voltage?
 

Thread Starter

matrixpt

Joined May 24, 2021
7
What are the LED specifications?
Led Specs-

D17 - 720mA
D22 - 450mA

Why is the meter on D22 reading 0.66V when SW2 is opened? Do the blue squares denote nets at 0V?
I have no idea why is showing 0.66....

Since you want to limit the voltage to the LEDs, that implies that the input voltage can change. Why don't you just regulate the input voltage?
The voltage on my car is not always 12v.

df
 

dl324

Joined Mar 30, 2015
13,527
The voltage on my car is not always 12v.
LED lights intended for autos will operate from the full range of voltages that could be present. The peak voltage from an alternator can be higher than 13.5V and it shouldn't harm the LEDs. If the voltage is below 12V, you could add a low voltage cutout if you're forget to turn the LEDs off.

D1-3 aren't required.
 

BobTPH

Joined Jun 5, 2013
4,046
I see no reason that you need anything other than two switches and two LEDs. But add two fuses if you want protection for the LEDs.

Bob
 

AnalogKid

Joined Aug 1, 2013
9,494
Probably a leakage current artifact of the simulation program. Add a 1K resistor in parallel with D22 to give the current an alternate path to GND.

ak
 

AnalogKid

Joined Aug 1, 2013
9,494
Rethinking ...

While my previous post was correct technically, there is a more simple way to add UVLO (under-voltage lock out) to this circuit, with one zener diode, one transistor, and two resistors.

ak
 

Thread Starter

matrixpt

Joined May 24, 2021
7
Probably a leakage current artifact of the simulation program. Add a 1K resistor in parallel with D22 to give the current an alternate path to GND.
Problem solved.

Probably a leakage current artifact of the simulation program. Add a 1K resistor in parallel with D22 to give the current an alternate path to GND.
according with my idea, i should use a 10k 3w resistor there right? or can i use a smaller w one?
 

AnalogKid

Joined Aug 1, 2013
9,494
Why so large? There is almost zero zener current. Also, you have a 1 K resistor in series with the battery and the LED, so there will be less than 12 mA of LED current.

ak
 
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