Why is the power of the resistor R10 chosen to be 0.5 and not 0.125 W? Also, what can be done to apply a 0.125 resistor instead of 0.5 watts?

Question

Electronics

Answer 1

Why is the power of the resistor R10 chosen to be 0.5 and not 0.125 W?

so that the resistor doesn't burn out. When 8 LEDs are lit, 8 times more current flows through them than through one LED (assuming the same brightness). 8 times more current through a resistor results in 8 times more heat. The rated power of the resistor is the maximum power dissipated (in the form of heat) at which the resistor will not burn out, but can work for a long time (years).

what can be done to apply a 0.125 resistor instead of 0.5 watts?

put one resistor 0.125 W after each of the LEDs HL6..HL13. According to the diagram, it is easy to assume that the resistance of each of these eight resistors should be 330 ohms (look at R1..R5). But for good, we need a calculation, which Victor is talking about .

Answer 2

Calculate the circuit parameters. You know the voltage of the power supply. You know the voltage drop across the LED (it is always indicated in the datasheet of the LED). Accordingly, you calculate the voltage drop across the resistor and can calculate the power that this voltage creates on a resistance known from the parameters of the circuit.
To reduce the power dissipated, you must either use a voltage that is not much greater than the voltage drop across the LED, or reduce the current through the LED by increasing the value of the resistor.

Answer 3

You provided almost all the information I asked for, except for the supply voltage. In further estimates, I will proceed from the fact that Upit \u003d 5 volts, the diodes are yellow (Upr ~ 2 volts) and glow all at once, except for one. It turns out the total current is about 60 mA, the power on R10 is about 170 mW. This is indeed over 0.125 watts, but there is no reason to use a half-watt resistor, 0.25 watts is enough.
Nevertheless, a resistor of 0.125 can be used if you use modern super-bright LEDs as LEDs - they glow perfectly from a current ten times less than the old ones that you have (the fact that they are exactly there can be seen from the excessively high current).
So, here's my advice - put super-bright diodes in the circuit, and this will allow you to use R10 with a power of 125 mW and a resistance of 330 ... 680 Ohms.