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Audio Description – Course 4, Load Matching for LED Drivers

– Clip 1 Introduction – Clip 2 Course Description – Clip 3 Test Parameters – Clip 4 Test Equipment – Clip 5 Overview – Clip 6 Transformer Ratio – Clip 7 Single LED 10 mm – Clip 8 Single LED 5 mm – Clip 9 matching load with resistor – Clip 10 3 Small LED’s in series – Clip 11 Flood Light SMD – Clip 12 40 LED’s Array – Clip 13 Calculations 1 – Clip 14 Summary – Clip 15 End of Part 8

Clip 1

Clip 1

The subject is related to impedance matching. However here we do not need to worry about transmission line calculations. The load is a diode and can only pass current in one direction. I will give some guidance of what you have to look out for. We use as example my LED driver I did build for a high resistive load. We then try to run a low resistive load and have to look out for the conditions required not to destroy this load. We compare standard led’s with SMD’s. At the end you should be in the position to decide what load you want to drive and how you have to construct your transformer.

Clip 2

Clip2

Course Description

Load matching options to drive LED’s

– Highlight impact of using low voltage LEDs in a high Voltage circuit
– Compare standard LED’s with high power SMD LED chips
– Show options to drive LED’s with voltages below 300 mV

Clip 3

 Clip 3

Test Parameters

1. High Voltage LED driver
2. Single standard LED
3. Flood light SMD chip
3. Array with 40 LED’s

Clip 4

 

Clip 4

Test Equipment
Tools

– EA, PS 2000 B, 84 V 5 A, Power supply
– Agilent/Keysight InfiniVision 3000 Series oscilloscope DSOX3014A
– External 19 Inch Monitor for Oscilloscope

Clip 45

 

Clip 5

Here is an overview of the components I display, inclusive my high resistive led driver. I will use some of the components in this videos but will go into details why batteries and direct current is mainly used. Let’s just say for now it is a cost question.

 

Clip 6

 

Clip 6

We start with 300 mV and measure around 60 volt peaks on the scope. this value would already be too high to drive an led. Let us see.

 

Clip 7

Clip 7

I have now selected the 10 mm LED and reduced the voltage to let us say almost nothing. The voltage on the scope with the load connected to the current does not exceed 13 Volt. We have light on the led. IMportant to note is that the current delivered plays a factor for the voltage drop. If there is no current delivered the voltage would drop to zero. In our example that is not the case. The power supply cannot show values below 300 mV and below 5 mA. To get the reading I would need to connect my precision DMM for both values.

Clip 8

 

Clip 8

I replaced now the 10 mm dled with the 5 mm led. They are both based on the same type with the same power ratings. I suspect it will work at this level as well. Important to note the power zero value is around 10-11 volt. The reason for this is the mains power radiation which is picked up from the high efficient Metglas core. Wee energized the load we read around 13 Volt. this is the surplus of voltage the led needs to emit light.Clip 9

 

Clip 9

To match now the load to the voltage of the led driver we add resistance as a high resistive load. We can so compensate for the low resistive load as one led. However that is not ideal because the resistor will get hot and losses energy. I connect in series high resistive potentiometers and can watch how the spikes on the scope disappear when more and more current is absorbed by the load, dropping from the original 51 Volt. You will notice that the brightness is much higher compared to before when the led was connected without a resistor. the reason is it did shunt the current to ground and was not able to transform it into light. the resistor does change that.

 

Clip 10

Clip 10

We connect now three small led’s in series. The would require 9 Volt and this has to be shown as an voltage increases on the scope to over 21 Volt. At 400 mV the scope measures 121 Volt. I can adjust the brightness very easy to full brightness. The scope is connected direct on the source terminal. In order to get the correct reading you need to connect the probe after the resistor to the load. Please look up Kirchoff’s Law. I explain in detail how to do it.

 

Clip 11

Clip 11

As comparison I use now a high power low resistive load. The SMD chips are high current consumers and drop the voltage very easy on any transformer. The Metglas core can easy deal with it but only in my overdrive mode where I remove resistance from the circuit to allow free oscillation. But as you can see it draw over 1 Amp of power at 3 Volt. that is half the power rating for this chip. This drive is build for such loads and has therefore no advantage in saving energy.

 

Clip 12

Clip 12

At last I connect now the high resistive load, the 40 LED’s in series. This driver is build for this kind of load. I have set it to over 2 Volt but go down now to 1.5 Volt. That is the reference voltage I want to use. The flicker of the light comes from the shutter of the camera. There is no visible flicker, however the frequency is low below 100 Hz. I will add now a formula and some details to consider on the board for you to help you with your calculations.

 

Clip 13

Clip 13

We integrate our measurements into the formula

Example for matching LED load

1 LED, Rating, 3 Volt and 20 mA

Measure transformer secondary voltage as 60 Volt

R= E/I = 60/0.02 = 3KOhm. This resistance is required to drive the load save for this output voltage

Measure between the resitor and the load. Voltage drop will not be visible when resistance is high on the source. Or to use 20 LEDs in Series.

Power delivery depends on transformer coil ratio and the wire thickness.
My secondary coil has 23 Ohm. In order to drive the load higher at the same applied voltage
I have to use a thicker wire. Instead of SWG26 I have to use SWG 20 to get it down to 10 Ohm.

Voltage drop depends on the available current. If almost no current is avialable the voltage
will go down to zero

Clip 14

 

Clip 14

Summary

Independent of the LED driver capability, load matching is very important and the
Consideration for what you need the driver. The system I did build can drive over
100 LEDs.
It can virtually drive LEDs direct from the earth, a potato and so on. Consider to develop
A driver for charging a battery. Your input voltage should not be higher than 1.5 Volt and
you like to Charge a 12 Volt battery in a Bedini fashion. I will develop new coil transformer
windings and wait until the Metglas C-cores arrive to combine it with the delayed Lenz
effect. If you compare this transformer with the first one in the first LED driver test where
I needed 11 Volt to drive a load then you can see where this should lead us. Transforming
energy from the environment and replenished from the environment to achieve a
COP > 1

Clip 15

Clip 15

The End Part 8
Load Matching for LED Drivers

 

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Clip 16