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Step 5Power Increase
The other requirement to increase the brightness is to increase the current flowing through the LED. This is relatively straight forward. Assuming a 5v logic supply to the LED, and from the data sheet the standard voltage of the LED is 3.6v. The protection resistor can be calculated by subtracting the LED voltage from the supply voltage, and then dividing this by the current.
R = (VS - VLED) / (iMAX)
R = (5 - 3.6) / 0.15
R = 1.4 / 0.15
R = 9.3 = 10R
It is however likely that the LED supply source may not be able to provide a sufficient current of 100mA, even if it is for a very short time. It may be necessary to power the LED through the transistor, possibly controlled by another transistor in series also capable of carrying the current.
In this circuit, the supply voltage of the op-amp should be used, as the 5v logic supply will be too small. There is a 0.7v drop over both transistors, and 3.6v over the LED, totalling 5v, and leaving nothing for a protection resistor. However, for the torch, the control can be placed over the power supply for the circuit.
VR = 9 - (3.6 + 0.7)
VR = 4.7v
R = 4.7 / 0.15
R = 31 = 33R
R = (VS - VLED) / (iMAX)
R = (5 - 3.6) / 0.15
R = 1.4 / 0.15
R = 9.3 = 10R
It is however likely that the LED supply source may not be able to provide a sufficient current of 100mA, even if it is for a very short time. It may be necessary to power the LED through the transistor, possibly controlled by another transistor in series also capable of carrying the current.
In this circuit, the supply voltage of the op-amp should be used, as the 5v logic supply will be too small. There is a 0.7v drop over both transistors, and 3.6v over the LED, totalling 5v, and leaving nothing for a protection resistor. However, for the torch, the control can be placed over the power supply for the circuit.
VR = 9 - (3.6 + 0.7)
VR = 4.7v
R = 4.7 / 0.15
R = 31 = 33R
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