Question: [![enter image description here](https://i.stack.imgur.com/Hio4d.png)](https://i.stack.imgur.com/Hio4d.png)

Hi Guys .. I am designing a few panels using LEDs for backlighting. Some of these panels have over 20 leds, using a 5v power source. So only one of these panels can draw around 500mA alone. I am planning on using the same PSU to power them all, but need a dimmer circuit to dim them all at once, but most of the dimmer circuits I have seen can only really do lower current draw, i.e. 2N2222 can only handle 800mA.

Any idea if this is possible with one high current dimmer, or do I have to build multiple dimmers ?

Answer: 
Pulse width modulation (PWM) is the most efficient way to do this. The basic principle is that you cycle the LEDs on and off at a speed fast enough that the eye can't detect a flicker - say 50 times a second. By varying the % on-time from 0 to 100% the LEDs can go from 0 to 100% brightness. The advantages are:

* The power circuit is very simple.
* No power is used while their off.

We need to know what is going to control the dimmer if we are to provide further information.
As others have mentioned, PWM is the most efficient method to drive the LED's.

I am just including this to expand on the concept, especially if there is any harness involve.

The use of an inductor ensure a constant current to the LED's as oppose to a pulsed current. 

By including a sense resistor you could include a simple control loop to maintain current as the load characteristics change (increased V due to temp)

Two sets of "freewheel" diodes are shown. The 1st is the diode that is used to commutate the current from the FET (to maintain current flow through the inductor). The second as part of a Zener+diode stack is for safety if the load goes open-circuit. 

NOTE: the zener/TVS needs to be sized to dissipate the energy within the inductor. It would only conduct during a failure situation and thus it does not need to be sized for continuous operation. 

![schematic](https://i.stack.imgur.com/rR9u7.png)

[simulate this circuit](/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2frR9u7.png) – Schematic created using [CircuitLab](https://www.circuitlab.com/)