Is this PCB OK for GC?

[samsagaz]

Hi guys, i was all the night trying to make an PCB for my new GC.

you think that this it good enough?

[pacificblue]

Did you calculate the power dissipation for all resistors correctly?

P=(U^2)/R for the bleeders and P=U*I for the LEDs resistor.

[samsagaz]

Originally posted by pacificblue
Did you calculate the power dissipation for all resistors correctly?

P=(U^2)/R for the bleeders and P=U*I for the LEDs resistor.

i didnt calculate it thanks for the Tip/Fix

Let me try to do it.....

Bleeders
-----------
P=(U^2)/R
P=(37^37)/2000
P=1369/2000 = 0.685W

So i think that needs to use like 2Watts resistors bleeders, right?

Led
-----
P=U*I
P=37*0.02=0.740W

To calculate the resistor value i need to use R = 37V / I right? An resistor like 1,9K will be OK?


Looks like needs to use an 2Watts resistor too

[AndrewT]

Originally posted by samsagaz
Bleeders
-----------
P=(U^2)/R
P=(37^37)/2000
P=1369/2000 = 0.685W

Led
-----
P=U*I
P=37*0.02=0.740W

To calculate the resistor value i need to use R = 37V / I right? An resistor like 1,9K will be OK?

make the resistor values larger.
Try 4k7 for the bleeder, if you think you need them.
Try 2mA to 5mA for the LED, not 20mA, i.e. 18k to 7k5.

[ratza]

I use 2.2k bleeders rated at 2W and they're stone cold at 30V. My LED is connected between the positive and the neagative rail and it has a 22k / 0.6W resistor which is also cold. The current through the LED is only 3mA, but the light is very visible. At 15mA it was very annoying.

[AndrewT]

Originally posted by ratza
I use 2.2k bleeders rated at 2W and they're stone cold at 30V.

we would all expect a 2W resistor to be cool when dissipating 400mW!!!

Originally posted by ratza
My LED is connected between the positive and the negative rail and it has a 22k / 0.6W resistor which is also cold. The current through the LED is only 3mA, but the light is very visible. At 15mA it was very annoying.

200mW through a 600mW will run warm.

Now he needs to calculate for his chosen values. Guessing is not permitted.

[samsagaz]

Originally posted by AndrewT

make the resistor values larger.
Try 4k7 for the bleeder, if you think you need them.
Try 2mA to 5mA for the LED, not 20mA, i.e. 18k to 7k5.

If i use 4k7 instead 2k, the diference will be that the cap will be discharged at half of time, right? (Will use 4k7)

ok, will change Led Resistor too... 10K is an easy value to find.

[samsagaz]

Someone know the Pin space of the 2Watts Resistors? im using altium, for 1/4 i was using Axial 0.3, now dont know wich to choice for 2Watts i dont have any 2Watts resistor in stock to check the space, i can choice Axial 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0....

[AndrewT]

calculate the dissipation in the resistors.
Adjust the resistor value to ensure the dissipation is <50% of rated maximum.
Then you don't need any 2W resistors.

[samsagaz]

Originally posted by AndrewT calculate the dissipation in the resistors.Adjust the resistor value to ensure the dissipation is <50% of rated maximum.Then you don't need any 2W resistors.

oh, nice, so for example

if i use 12k for Bleeders, i can use 1/4W resistor. and can use 10K for led and can use 1/4W too, right?