Determine the function of the LED circuit shown In Fig P5135

Determine the function of the LED circuit shown In Fig P5.135. LED D_2 has a V_f of 1.3 V and requires a minimum of 1 mA of current before it\'s light becomes visible to the naked eye. Consider the LED circuit of Fig. P5.136. Both LEDs have a V_f of 0.8 V and can safely conduct no more than 15 mA of current when energized. Determine the function of the circuit and choose appropriate values for R_1 and R_2.

Solution

5.135) The function of the LED circuit is that when the input voltage of the circuit reaches 5V the LED lights up.

This is an indication that the circuit has a output of exactly 3.7V,

Because 3.7+1.3=5V

5.136) The function of the circuit is to produce blinking LED\'s alternatively. During positive half cycle D1 lights UP and during negative half cycle D2 lights UP.

So R1=R2=1K can be chosen assuming current for each LED as 20mA.