LEDs are used in most of our lighting requirements. Traditional filament lamp or more modern mercury lamp or CFL lamps are being rapidly replaced by the LED lamps due to high light intensity to power ratio and easy to use control methods. Although our home LED lights are powered by AC mains voltage actual LEDs are DC devices, the driver inside the bulb converts AC mains voltage to DC voltage required to power the LED. Today we are going to see how to build a high powered 18V LED driver circuit using minimal components. We are going to use A3120 optocoupler as the key component.
What is A3120?
A3120 is an optical isolator IC, simply said A3120 is a optocoupler. But A3120 is different from normal optocoupler which as input LED and a output open collector transistor. A3120 also has a LED tied to it’s input but as output it has an inbuilt gate driver circuit that can drive a MOSFET or an IGBT without any additional components. You can see the physical appearance of the A3120 optocoupler in below image.
Pinout of A3120:
A3120 gate driver optocoupler comes in a 8 pin DIP package with both THT and SMD options. Lets identify the pinout of the A3120 optocoupler using image given below.
Let’s see more details on the pin functions of the A3120 gate driver optocoupler. Functions of each pin are listed out below.
· Pin 1 — N/C — Not connected to anything
· Pin 2 — Anode — This is the positive pin of the input LED
· Pin 3 — Cathode — This is the negative or cathode of the input LED
· Pin 4 — N/C — Not connected to anything
· Pin 5 — VEE — This is the negative or ground (GND) connection of the gate driver circuit. Usually this is connected to the GND of the power side or the transistor voltage.
· Pin 6 — V0 — This is the actual gate driving pin. This should be connected to the gate of the MOSFET or the IGBT. A series resistor can be used
· Pin 7 — V0 — Same as the pin 6
· Pin 8 — VCC — This is the positive supply voltage of the gate driver circuit. Usually this is connected to the positive voltage of the load voltage.
Features of MHL21336:
Lets identify some of the main features of A3120 gate driver optocoupler as mentioned in it’s datasheet.
· 2.0A minimum and 2.5A maximum peak output current
· 1500V isolation voltage
· Under voltage locked out protection
· Wide operating voltage of 15V to 30V DC
· 500ns switching speed / time
· Wide operational temperature range
Basic Circuit Diagram:
Basic circuit diagram of high power 18V LED driver circuit using A3120 gate driver optocoupler is given in the below image.
Key Components :
We will need several other components with A3120 in order to successfully complete the circuit. All the components are given with their corresponding order links from https://www.utsource.net/ So, you can order the components easily.
1. A3120 Gate driver optocoupler
2. 270Ω resistor
3. 10kΩ resistor
4. 0.1uf capacitor
5. IRG4BC30KD IGBT
Tools Needed:
1. Soldering Iron
2. Iron Stand
3. Flux
4. Nose pliers
Step By Step Guide:
Step 1: Arrange the components.
Step 2: Solder the 270 ohm resistor or to the input anode signal pin of the A3120 optocoupler.
Step 3: connect pin 3 of A3120 which is negative pin of the input LED to the signal ground pin.
Step 4: Solder the power connections as shown in the circuit diagram.
Step 5: Connect load power pins to the A3120 gate driver power pins as shown in the circuit diagram.
Step 6: Connect both pin 6 and 7 to the gate of the IGBT through a 10k resistor.
Step 7: Connect the rest of the power connections and LED to the circuit as shown in the circuit diagram.
Step 8: Connect 18V supply to the load supply. This should be DC power.
Step 9: Supply +5V to the input pin to turn on the LED.
How It Works:
When an input signal is given in to the positive input pin of the A3120 optocoupler’s input LED it will set the gate voltage of the driver IGBT according to the input voltage. This will cause the LED to turn on.
Conclusion:
This circuit is very useful in high power portable flashlight or a food light. You can use a pwm signal generator or a variable resistor to vary the input voltage provided to the input LED of the A3120. By doing so you can control the brightness of the LED light proportionally to the input signal’s duty cycle or the voltage.
