This small circuit for Simple 3V LED Driver using IC LT1937 helps to power LED.
It takes big battery power and make it 3V for LED.
Chip LT1937 does good job by keeping power steady.
LED gets enough power to shine bright all time.
Block Diagram:
To understand how it works look at block diagram above:
LT1937 uses special control way to keep power steady.
Each cycle for a switch Q1 turns ON.
It measures current and adds ramp signal and sends to part A2.
When signal gets too big then A2 turns switches OFF.
A2 checks this using help from A1 which compares feedback with 95mV reference.
This helps A1 control how much current goes out.
If A1 output goes up then more current goes to output.
If A1 output goes down then less current goes to output.
Circuit Description:
Parts List:
| Category | Item | Quantity |
|---|---|---|
| Resistors(All resistors are 1/4 watt unless specified) | 4.7Ω 1% | 1 |
| 100k | 1 | |
| Capacitors | Ceramic 0.47µF | 1 |
| Electrolytic 2.2µF 25V | 1 | |
| Semiconductors | IC LT1937 | 1 |
| Diode BAT85 | 1 | |
| Straw hat white LEDs 5mm | 4 | |
| Coil inductor 20uH | 1 | |
| Push on switch | 1 |
LT1937 can run 4 LEDs in series at low current like 4mA from a 4.2V battery.
At 4mA no pulse is skipping then if using parts meant for 15mA.
If current goes lower then it starts skipping pulses and causing small ripple.
Still average current stays stable which is even down to 0.
Use 22µH inductor which works well at 1.2MHz and has low resistance.
Use ceramic capacitors for X5R or X7R types are best.
Use 2.2µF for input C1 and 0.47µF for output C2.
Use Schottky diode with fast and low voltage drop so less power losses
But higher diode capacitance causes more switching loss at 1.2MHz.
Best to use Schottky rated 100 to 200mA.
LED current is set by resistor R2.
Current = 95mV / R1.
Use 1% resistor for best LED current.
Formulas and Calculations:
This formula helps set LED current using LT1937 chip.
Main formula:
R2 = 95mV / ILED
This means:
The chip uses a 95mV reference voltage at the ISET pin.
By choosing resistor R2 we can decide how much current flows through LED.
Rearranged formula:
ILED = 95mV / R2
Example:
We want 20mA LED current:
R2 = 0.095V / 0.02A = 4.75Ω
Pick nearby resistor: 4.7Ω or 5.1Ω
Important:
Check resistor power rating:
P = I² × R2
Ensure resistor can handle the heat with 1/4 watt is good for most cases.
Summary:
Use R2 = 95mV / ILED
This sets LED current based on internal 95mV reference of LT1937.
How to Build:
To build a Simple 3V LED Driver Circuit using IC LT1937 follow the below mentioned steps for connection purpose:
- Give stable power in range with IC LT1937 needs and check datasheet for exact voltage.
Connect Parts:
- Wire LT1937 like in datasheet circuit.
- Connect inductor, capacitors, Schottky diode and resistor R2.
- Check diode and capacitor have correct direction.
Inductor:
- Use 22µH inductor for low loss at 1.2MHz and low wire resistance for DCR.
Capacitors:
- Use 2.2µF for input and 0.47µF for output.
- Use ceramic type X5R or X7R.
Diode:
- Use Schottky diode rated 100 to 200mA.
- Check forward voltage and capacitance.
- Turn ON the power and check output voltage and LED current.
- Try with different loads and ensure it stays stable.
Adjustments:
- If result are not good then change resistor or other parts to fix the output.
Conclusion:
Simple 3V LED Driver Circuit using IC LT1937 is small and is good for powering 3V LEDs from bigger voltage.
This circuit keeps LED bright and steady and is good for many LED projects.