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I am working on to build a dimmer for led lamp. Led driver AC input is about 220V and output of the driver is 70V under load. I placed a npn transistor (mje13007) between led ground and led driver output ground. I am driving this transistor with a PWM source.When duty cycle gets bigger, it starts to flicker. What is this problem and how to overcome?

Circuit

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  • \$\begingroup\$ What are the CV or CC specs vs load V vs I? The flicker implies inadequate supply or excess load current. Should we guess? \$\endgroup\$ Commented Mar 26, 2017 at 16:18
  • \$\begingroup\$ The answer of Ignacio Vazquez-Abrams makes sense.Circuit fault and is shutting down \$\endgroup\$ Commented Mar 26, 2017 at 16:31
  • \$\begingroup\$ sorry for suggesting "usage fault" not circuit fault for not telling parameters above, but similar idea. \$\endgroup\$ Commented Mar 26, 2017 at 17:37

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The problem is that the driver is detecting the naive PWM mechanism as a circuit fault and is shutting down. The fix is to use a driver that supports PWM natively.

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  • \$\begingroup\$ If I remove the PWM source and drive the transistor with a potentiometer,still have the same problem? \$\endgroup\$ Commented Mar 26, 2017 at 16:11
  • \$\begingroup\$ My point is that you cannot make this modification to the circuit at all. The output must only be connected to LEDs. \$\endgroup\$ Commented Mar 26, 2017 at 16:11
  • \$\begingroup\$ How does the circuit sense the modification? \$\endgroup\$ Commented Mar 26, 2017 at 16:12
  • \$\begingroup\$ It's comparing the current through the LEDs with what it should be. If they're not the same then it shuts down for safety reasons. \$\endgroup\$ Commented Mar 26, 2017 at 16:13
  • \$\begingroup\$ All led driver ICs have that kind of protection? \$\endgroup\$ Commented Mar 26, 2017 at 16:14

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