| Re: LED dimmers [message #303717 is a reply to message #303706] |
Sun, 17 July 2016 16:50   |
Keith V
Messages: 2337
Registered: March 2008
Location: Mounds View,MN
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not into drawing pictures, but yours are basically backwards.
I'd like to know how you are powering these circuit on the top, looks like magic to me since the PWM is on LEDs will be dropping all the voltage and the PWM will be at zero V. When the PWM is off it does have 12v but it cant draw any power since those Light emitting diodes aren't conducting
The bottom circuit is also pretty magical, you have a circuit that can run on zero power. When the PWM is ON, there is ( hopefully ) very little voltage drop across the device, and when the PWM is on, there is ( again hopefully ) 100% voltage drop across the device.
Both these scenarios leave no power to run the PWM
The problem with your drawing is it doesn't show the control circuit or where it gets it's power.
The dimmer has 2 inputs and 2 outputs, 1 positive, one negative.
I opened the box and the positive line goes straight through, while the ground side has the PWM driver in the way.
So the controller absolutely does know where it is in the circuit, it is switching the ground side.
The pwm driver is on the low side, meaning on the ground wire, I'm sure there are many reasons to do it this way, but Id bet it's mostly cost as you don't need a boost circuit to turn on the high side switch.
( FETs need the gate to be 2-5 volts above the source voltage to turn on, transistors need less, like .6-.7v )
Keith Vasilakes
Mounds View. MN
75 ex Royale GMC
ask me about MicroLevel
Cell, 763-732-3419
My427v8@hotmail.com
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