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PWM the Secondary Side of a 30W LED Driver Closed

2022-04-28

Green Earth

Secondary side PWM is no good .Bimpelrekkie has stated some reasons why.You could discard the cheap chip but it does have a low parts count even if EMC and inrush current issues are addressed.If you want to keep the chip you could experimentally change R sense to a larger value and note the lower LED string current giving a dimmer result.You should be able to get a reasonable control range .

If the control range is enough for you then hook up a mosfet and an optocoupler to get things safely isolated from the mains .The mosfet will be cheap because the voltages and currents it sees are low .The opio can be a cheap 4N38 because speed is not important here.

The mosfet does not waste any more power because it is acting as the current sense resistor

Closed. This question needs details or clarity. It is not currently accepting answers. Want to improve this question? Add details and clarify the problem by editing this post. Closed 2 years ago. Improve this question

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EDIT:

I have replaced the FL7732 circuit with the circuit I actually have ("D29B 6L15"). In addition I've added another question.

Please also note that I've accepted that using the 30W driver is not the way to go. I am asking, because I want to understand SMPSs and how they behave.

Where do I find reasonably priced LED-driver, which I can modify for variable currents?

...................

This is a follow up question to modify 30W led driver

Here is the schematic of the led driver:

I have added a FET on the secondary side and PWM the LEDs.

As expected the voltage of the capacitor rises and the brightness of the LEDs changes only very little until 20% PWM at which point the LED driver apparently can't rise the voltage any longer.

The LEDs are rated twice the power I use them. Receiving a little bit more current while the PWM turns them on should IMO not hurt them.

However I don't know if this could hurt the driver itself.

So my questions:

is controlling the brightness using a FET and PWM safe for this circuit?

what could happen / what should I pay attention to?

is there a cheap / easy way to use existing LED drivers (flyback) to change the brightness of the LEDs.

The FL7322 circuit has a diode, resistor and capacitor across the primary winding. How important are those.

Â·OTHER ANSWER:

...................

EDIT:

I have replaced the FL7732 circuit with the circuit I actually have ("D29B 6L15"). In addition I've added another question.

Please also note that I've accepted that using the 30W driver is not the way to go. I am asking, because I want to understand SMPSs and how they behave.

Where do I find reasonably priced LED-driver, which I can modify for variable currents?

...................

This is a follow up question to modify 30W led driver

Here is the schematic of the led driver:

I have added a FET on the secondary side and PWM the LEDs.

As expected the voltage of the capacitor rises and the brightness of the LEDs changes only very little until 20% PWM at which point the LED driver apparently can't rise the voltage any longer.

The LEDs are rated twice the power I use them. Receiving a little bit more current while the PWM turns them on should IMO not hurt them.

However I don't know if this could hurt the driver itself.

So my questions:

is controlling the brightness using a FET and PWM safe for this circuit?

what could happen / what should I pay attention to?

is there a cheap / easy way to use existing LED drivers (flyback) to change the brightness of the LEDs.

The FL7322 circuit has a diode, resistor and capacitor across the primary winding. How important are those.

PWM the Secondary Side of a 30W LED Driver Closed 1

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