B
[email protected]
- Jan 1, 1970
- 0
I want to use LEDs in a motor vehicle, but they must be dimmed to
about 10% of their daytime brightness at night to avoid blinding the
driver. I need a simple, cheap circuit to do this.
My thinking was to use a light dependent resistor (ldr) to switch a
transistor (tr) that then added a resistor (R2) in parallel with the
LED. This resistor would reduce the current in the existing resistor
R1 (as it is in series with it) thereby dropping the current available
to the LED. But would it also change the voltage substantially at the
resistor/LED junction so that the LED no longer lights?
+V--\-----------------\
| |
ldr R1
| |
| --R2--+
| / |
+---Tr\ LED
| \ |
| | |
0V---/-------/--------/
Remember this is in a motor vehicle so there is plenty of spare power
and heat sinking available.
thanx, bye.
about 10% of their daytime brightness at night to avoid blinding the
driver. I need a simple, cheap circuit to do this.
My thinking was to use a light dependent resistor (ldr) to switch a
transistor (tr) that then added a resistor (R2) in parallel with the
LED. This resistor would reduce the current in the existing resistor
R1 (as it is in series with it) thereby dropping the current available
to the LED. But would it also change the voltage substantially at the
resistor/LED junction so that the LED no longer lights?
+V--\-----------------\
| |
ldr R1
| |
| --R2--+
| / |
+---Tr\ LED
| \ |
| | |
0V---/-------/--------/
Remember this is in a motor vehicle so there is plenty of spare power
and heat sinking available.
thanx, bye.