# Creating 1.12v ac at 22.5khz

#### BGT

Oct 22, 2020
15
1.12 volts AC
22.5 khz
45ma

This is the voltage needed to light up a string of 100 LED lights, and I would like to take that power from a small DC supply. (any thing from 1.5v to 18v DC)

Where do I even start ?

could there be a one off component that I could buy ?

#### Audioguru

Sep 24, 2016
3,650
LEDs do not work from 1.12VAC at 22.5kHz. Also, LEDs do not create 1.12VAC at 22.5kHz.
If the LEDs are blue or white and are in series then you need to power them from about 320VDC at about 10mA.

The color of an LED tells you what voltage it needs. The size of an LED and how bright you want it tells you how much current it needs. The way the 100 LEDs are wired tells you all about it.

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,476
Where do I even start ?
- type of LED
- proposed wiring
- etc.

Why do you think the parameters you have given are suitable for driving 100 LEDs?
Why would you want to drive LEDs with AC anyway?
Why at 22.5 kHz?
LEDs are driven by DC and can be damaged when AC is applied.

#### BGT

Oct 22, 2020
15
- type of LED
- proposed wiring
- etc.

Why do you think the parameters you have given are suitable for driving 100 LEDs?
Why would you want to drive LEDs with AC anyway?
Why at 22.5 kHz?
LEDs are driven by DC and can be damaged when AC is applied.
OK, will try and explain.

I have a couple of sets of solar coloured LED lights that for whatever reason are no longer working properly. It is a string of 50 lights made up of 4 colours Yellow Red Blue and Green.

Not sure if they are in series or parallel but they are all on the same pair of wires.

If I apply 4v DC to these wires the yellow and Red light up. If I then reverse the polarity the yellow and Red go out and the Blue and green come on.

The lights seem to come on at about 2.4 V and reach full brightness at 3.5 Volts DC.

When I test a set of these lights that is working correctly I have found that when all the lights are on steady, then the current is 1.12 VAC and my multimeter tells me the Hz s 22.5 kHz (not really sure how to use this function on my multimeter)

I am presuming the alternating current is lighting each pair of colours in turn and the rapid speed gives the impression that they are on constantly.

I was thinking if I could create a 1.12 VAC of a fastish Hz then I could use these lights instead of sending them off to landfill - I'm also just curious in how all this sort of stuff works, and at the moment have a fair bit of spare time.

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,476
1.12v AC and
This makes no sense.
Current is measured in amperes (A), voltage is measured in volts (V). There is no such thing as a current in xxx volts.
What exactly do you measure: current into the LEDs or voltage across the LEDs?
We need both voltage (between the two wires) and current (in series with one of the wires) to help with a suitable driver replacement.

my multimeter tells me the HZ s 22.5k (not really sure how to use this function on my multimeter)
It may be so that the original controller operates at 22.5 kHz. However, for non-flickering LEDs a frequency of 100 Hz or more will suffice to make the flickering unnoticeable for the human eye.
You are right in assuming that AC will be required to drive all colors - according to your measurements and explanation.

So far the likely setup will consist of:
1) A power supply that delivers enough power (voltage , current) to drive the LEDs. Do you have such a power supply (possibly from the original controller)?
2) An oscillator that generates an control signal at 100 Hz or more. A simple circuit can be built from a 555 timer IC.
3) an H-bridge driver that will be controlled by said control signal and will deliver the AC power to the LEDs .

Once we have the missing information, we can start to put the puzzle pieces together.

#### kpatz

Feb 24, 2014
334
1.12V isn't really accurate. The controller is generating AC pulses that your meter is probably misreading due to the duty cycle and pulse shape. More likely it's 3.5-ish volts to get the LEDs to light at all. It's alternating the polarity (generating highish frequency AC) to make all the colors light. When it's in a flashing mode (assuming it has one) it's changing the relative times or duty cycle of the pulses to make the LEDs of each color light differently.

Judging from the voltage, the LEDs are in parallel.

If you want them to all light, you could use something simple like a 555 timer circuit or an oscillator made from a couple of NAND gates, or op amps. The controller box it came with likely has a microcontroller to control the lights and make them fade and flash.

#### BGT

Oct 22, 2020
15
below is an image of the controller, the 1.12 VAC was measured between the two wires coming out of the left hand side, these are the wires connected to the LEDs

As to current, I have only measured this from the input. (the two black wires) and at 1.5 V DC I measured 45mA when all the lights are on steady.

The problem/fault with this controller is it now forgets what mode it is in and reverts to flashing (need to press the mode button 7 times to get back to steady) Obviously the easy option is just to buy a whole new set (£5 ish) including lights. But I would love to know how to modify or build a new controller that would just keep all lights on steady.

Last edited by a moderator:

#### Audioguru

Sep 24, 2016
3,650
You show the circuit (4 pins IC) from a cheap low power solar garden light that takes the 1.2V from a single Ni-MH battery cell and steps it up to a few volts with the inductor (it looks like a resistor) and Schottky diode at 250kHz to 500kHz. Then the diode and capacitor on the right side filter the high frequency pulses to drive one or a few LEDs. The larger IC shown might have 7 LED patterns built into it.

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,476
Sounds all logical but doesn't explain the behavior of the different colors lighting with reversed voltage. The step-up alone would create a unipolar voltage, especially with the diode and the capacitor we see.

The IC is possibly a dedicated controller. A typical microcontroller wouldn't be able to drive 50 LEDs.

@BGT : can you show us close-up photos of the 2 chips (4 pin and 8 pin) such that we can read what's printed on them? Alternatively copy the labels down if they are not well readable on a photo.

#### Audioguru

Sep 24, 2016
3,650
AliExpress sells a new version of this circuit but they do not ay much about it.

#### Attachments

• solar light controller.png
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#### BGT

Oct 22, 2020
15
if only I could default it to the 'Steady' mode, but unfortunately when they start to go wrong hey like to go to the horrible flashing on and of mode.

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