LED flicker

[aptsys]

For a modulated carrier at 100% modulation 2/3 of the power is in the carrier and 1/3 in the modulation. If the LEDs only see the 50Hz (which I doubt is actually the case) what happens to the carrier power? Well I believe it goes to heating the LEDs which would explain what I found in my experiments above, post 33.

No, the lamps will either have a simple current limiting resistor or a switching regulator in the case of 12V modules, but neither methods care about the input waveform - once rectified and filtered by the main input capacitor, the LEDs or the driver see plain DC. The input waveform is integrated in its entirety less losses of the rectifier diodes and heating due to the ESR of the capacitor.

 

[hard-work]

Feeding an LED driver with 40,000 Hz may work, it may not, it may make the LED driver so unstable in operation that damage to driver and/or LED elements occurs.

When the light cord is pulled the LED lights flicker as the transformer/LED lamps adjusts, then constantly staying on with no flicker. When the lights have been on for a while and the they are switched off and soon after on, they flicker.

 

[bernardgreen]

I've never seen a 12V LED lamp without a bridge rectifier and reasonably sized capacitor after it

This was found in a LED lamp bought in Spain. Changing mains frequency altered the brighteness as the series capacitor was the current control.

Resistors did not have markings indicating their value.

 

[aptsys]

This was found in a LED lamp bought in Spain. Changing mains frequency altered the brighteness as the series capacitor was the current control.

View attachment 118208

Resistors did not have markings indicating their value.

Note, I mentioned a 12V lamp - they operate on both DC and AC so a series capacitor current limiter is not a possible topology.

 

[aptsys]

When the light cord is pulled the LED lights flicker as the transformer/LED lamps adjusts, then constantly staying on with no flicker. When the lights have been on for a while and the they are switched off and soon after on, they flicker.

The electronic transformers designed for halogen lamps are very simple devices. They simply contain a self-exciting oscillator which form the high frequency carrier and a transformer - the driver rides the mains AC waveform but the output transformer operates at the frequency set by the oscillator. At low loads, there isn't enough current through the primary of the transformer to keep the oscillator stable - all you're seeing is the unstable behaviour of the circuit as it attempts to run as intended.

The standard electronic transformers contain no timing IC or SMPSU chip (the only semiconductors are the pair of switching transistors and a few diodes and a diac), so struggle with loads not exceeding their minimum.

 

[bernardgreen]

Note, I mentioned a 12V lamp.

The same circuit with different values will work on 12 volts AC, ( maybe I should have removed the reference to mains )

 

[aptsys]

The same circuit with different values will work on 12 volts AC, ( maybe I should have removed the reference to mains )

True, but 12V lamps are designed to work on both AC and DC so that they can be used with constant voltage drivers.

 

[winston1]

No, the lamps will either have a simple current limiting resistor or a switching regulator in the case of 12V modules, but neither methods care about the input waveform - once rectified and filtered by the main input capacitor, the LEDs or the driver see plain DC. The input waveform is integrated in its entirety less losses of the rectifier diodes and heating due to the ESR of the capacitor.

If this is the case why do the manufacturers stipulate DC or 50/60Hz AC?

 

[aptsys]

If this is the case why do the manufacturers stipulate DC or 50/60Hz AC?

So as not to confuse the customer. They will work at any frequency although at low frequencies, flicker will be evident, and higher frequency you may get greater losses in the rectifier (although longer life overall).

 

[winston1]

So as not to confuse the customer. They will work at any frequency although at low frequencies, flicker will be evident, and higher frequency you may get greater losses in the rectifier (although longer life overall).

Sorry I don't buy that. The ones I tried doubled their power draw at 30kHz and got very hot. I don't believe that was due to the rectifier. High speed rectifiers have been available for many years.

 

[bernardgreen]

High speed rectifiers have been available for many years.

but unlikely to be found in a bridge rectifier intended for 50/60 Hz AC.

At high frequency the parasitic capacitance of the diodes comes into the equation. The capacitance is a bi-directional low impedance path shorting out the diode. Significant current flows from AC1 to AC2 through the parasitic capacitors even when the + and - outputs are not connected. This current heats the internals of the bridge rectifier.

 

[rules&rulers]

Just tell your neighbour to call in a registered experienced electrician to check the installation and fit the correct lighting.

Remember that bargain priced fittings are cheap for a reason.

 

[hard-work]

Just tell your neighbour to call in a registered experienced electrician to check the installation and fit the correct lighting.

Remember that bargain priced fittings are cheap for a reason.

We do not need an electrician. It points to the transformer as this thread will tell you.

 

[rules&rulers]

We do not need an electrician.

FFS you aint got a clue. the clue is asking on a diy site. sorry not going to comment on this post again.

 

[hard-work]

not going to comment on this post again.

Wise.