Darlington transistor led driver

The internal logic for each channel is shown to the right. It is well suited for driving higher powered 7-Segment displays, solenoids, relays, fans, small motors and many other low to moderate power devices. The driver is used on the low side of the load which means it is connected between the load and ground and are used to sink current to ground. Since the two transistors are used in this configuration therefore the base voltage must be greater than 1.

Similarly, the current gain of next transistor,. But the base current of the second transistor,. Substituting in the above equation,. In the above relation individual gains are neglected and the total equation is approximated as.

Consider the following circuit where Darlington pair is used to switch the load that is rated at 12V and 80W. The current gains of first and second transistors are given as 50 and 60 respectively.

So, the base current required to make the lamp fully ON is calculated as follows. From the above calculation, it is clear that with small base current we can switch the larger lamp loads. This small base input voltage can be applied from any microcontroller output or any digital logic circuits.

Darlington transistors are mainly used in switching and amplification applications for delivering a very high DC current gain.

Some of the key applications are high and low side switches, sensor amplifiers and audio amplifiers. For light-sensitive applications photodarlingtons are used. Let us look at the operation of a Darlington transistor for a specific application.

The below figure shows driving of an LED using the Darlington transistor. A switch at the base terminal can also be replaced with a touch sensor so that for a touch sensing LED turns ON. A k ohm resistor acts as a protective resistor for the pair of transistors. In case of power or voltage amplifiers the load resistance at the output is very low to have high current flow. The Darlington transistor circuit lends itself to use in small driver chips for LEDs and other small devices. The high current gain of the Darlington circuit means that these small driver chips can be used to interface LEDs and other devices to logic chips.

Darlington pair circuit in linear power regulator The Darlington pair circuit finds many applications as the series pass element in a linear regulator.

Circuit using Darlington as PSU series pass transistor In power supply applications, the series pass element is required to pass high levels of current. Darlington transistor in audio output circuit Another Darlington circuit application is within audio power amplifiers. Photo-darlington circuit The Darlington configuration is used in many photo applications.

Led drivers The Darlington transistor circuit lends itself to use in small driver chips for LEDs and other small devices. Connection Point 4. Calculations 5. Loop 6. Input 7. Decision 8. LCD 9. Keypad Software Macro External Interrupt Timer Interrupt. Transistor Power handling Current gain BC