This circuit is designed to simultaneously test up to three LEDs connected in series. By employing a higher supply voltage, it’s easy to expand the number of LEDs tested. This uncomplicated LED TV Backlight Tester incorporates a current source equipped with a potentiometer for current adjustment. The current source utilizes a TL081 opamp. The opamp’s output current passes through the diode and R2. The voltage drop across R2 is looped back to the inverting input and compared with a reference voltage set by R1, which is then applied to the non-inverting input.
The adjustment range covers approximately 0–30 mA, making it suitable for testing regular LEDs. If desired, you can attach a multimeter to the LED to measure the voltage on the LED TV Backlight Tester. For the power source, a practical choice is a small laboratory power supply set to 5 V output. It’s convenient to have a potentiometer with a scale for direct monitoring of the LED current flow. To calibrate the scale, you can temporarily substitute an ammeter for the LED.
The TL081 is an affordable high-speed JFET input operational amplifier with an internally trimmed input offset voltage (BI-FET IITM technology). This device requires minimal supply current while maintaining a significant gain bandwidth product and fast slew rate. Additionally, precisely matched high voltage JFET input components ensure extremely low input bias and offset currents. Pin compatibility with the standard LM741 and the use of the same offset voltage adjustment circuitry make the TL081 a suitable choice. This feature enables designers to enhance the overall performance of existing LM741 designs immediately.
TL081 features and specifications:
- Supply Voltage: 7V to 36 V
- GBP – Gain Bandwidth Product: 3 MHz
- SR – Slew Rate: 13 V/us
- CMRR – Common Mode Rejection Ratio: 70 dB to 86 dB
- Operating Supply Current: 1.4 mA
- Input Bias Current: 200pA
- Power Dissipation:670mW
- Available in 8-Pin PDIP, SOIC Packages