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Solid States Devices => solid state devices => Topic started by: nix85 on February 18, 2021, 05:56:33 PM

Title: How this LED board works on range of voltage
Post by: nix85 on February 18, 2021, 05:56:33 PM
https://www.aliexpress.com/item/32974073528.html?spm=a2g0o.productlist.0.0.38564776VFItij&algo_pvid=334057b3-ec45-4bc9-b8e4-cee8bf777d47&algo_expid=334057b3-ec45-4bc9-b8e4-cee8bf777d47-4&btsid=0b0a555e16135992174055930eef8e&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_

So input voltage is AC or DC 10-30V.

We can see it rectifies AC and has a cap to smooth it.

There are 12 LEDs. LEDs need 2-3V.

If they are in series and input is 30V voltage would be 2.5V per LED, just right.

But what if it's 10V, then voltage across each diode is only 0.8V.

Is it somehow detecting voltage below 30V and using that inductor as boost converter?

Or maybe LEDs are in parallel with a zener to keep the voltage around 3V?

If that's the case most energy would be dissipated across the resistors, not the LEDs. (unless resistors are perfectly chosen for that particular voltage).

What you think?

Title: Re: How this LED board works on range of voltage
Post by: nix85 on February 18, 2021, 10:31:00 PM
This might be the answer https://en.wikipedia.org/wiki/Voltage_regulator#Switching_regulators

Switching regulators rapidly switch a series device on and off. The duty cycle of the switch sets how much charge is transferred to the load. This is controlled by a similar feedback mechanism as in a linear regulator. Because the series element is either fully conducting, or switched off, it dissipates almost no power; this is what gives the switching design its efficiency. Switching regulators are also able to generate output voltages which are higher than the input, or of opposite polarity — something not possible with a linear design. In switched regulators, the pass transistor is used as a "controlled switch" and is operated at either cutoff or saturated state. Hence the power transmitted across the pass device is in discrete pulses rather than a steady current flow. Greater efficiency is achieved since the pass device is operated as a low impedance switch. When the pass device is at cutoff, there is no current and dissipates no power. Again when the pass device is in saturation, a negligible voltage drop appears across it and thus dissipates only a small amount of average power, providing maximum current to the load. In either case, the power wasted in the pass device is very little and almost all the power is transmitted to the load. Thus the efficiency of a switched-mode power supply is remarkably high-in the range of 70-90%.

Switched mode regulators rely on pulse width modulation to control the average value of the output voltage. The average value of a repetitive pulse waveform depends on the area under the waveform. If the duty cycle is varied, the average value of the voltage changes proportionally.

Like linear regulators, nearly complete switching regulators are also available as integrated circuits. Unlike linear regulators, these usually require an inductor that acts as the energy storage element.[2][3]The IC regulators combine the reference voltage source, error op-amp, pass transistor with short circuit current limiting and thermal overload protection.
Title: Re: How this LED board works on range of voltage
Post by: gyulasun on February 18, 2021, 11:21:43 PM
Yes, the better LED lamps include switching regulators.
Here is a tear down video on the circuit included in a 5W, 12V AC/DC type lamp:
https://www.youtube.com/watch?v=i-Roc5TLdnw     
Title: Re: How this LED board works on range of voltage
Post by: nix85 on February 19, 2021, 12:40:13 AM
Tnx