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LDO gets hot when using a relay module?
- Thread starter BucketOfFish
- Start date
Sorry, I didn't catch that at first.
So we know coil needs 85ma to operate.
Say for instance a 9v source was used directly, would we use a 36 ohm dropping resistor?
36r+70r (coil)=106ohms X .085=9v
Or would it be 59 ohms calculated for the coil, making it a 47 ohm resistor?
Sorry, I don't want to hijack the conversation.
Please answer op first.
So we know coil needs 85ma to operate.
Say for instance a 9v source was used directly, would we use a 36 ohm dropping resistor?
36r+70r (coil)=106ohms X .085=9v
Or would it be 59 ohms calculated for the coil, making it a 47 ohm resistor?
Sorry, I don't want to hijack the conversation.
Please answer op first.
davenn
Moderator
of course that still isn't going to work, as there is no voltage to the S pin to turn on the transistor
you still need to take a probe wire from the 4.5V to the S pin that can be tapped on and off to activate the relay
cheers
Dave
of course that still isn't going to work, as there is no voltage to the S pin to turn on the transistor
you still need to take a probe wire from the 4.5V to the S pin that can be tapped on and off to activate the relay
View attachment 23396
cheers
Dave
Dave you are correct.
I did write in post # 21: "Switch" S as before
The op did that already in post #1 (that isn't the problem he faced):
"When the signal (S) pin is low, the module and LED are off.
When S is high, the module and LED are both on."
So,How "hot" does the LDO get?
to answer this we need to know which part is it.
Pd(LDO)=4*85mA=0.34W
Thermal resistance of a TO-220 packages case-to-ambient is about 50°C/W to 60°C/W.
Tcase over ambient temp. =0.34*60=20°C
so for a 25°C room we get 25+20= 45°C case temp.
this can't be related to as truly "hot".
it doesn't pose any problem to the LDO and no heat-sink is actually required.
to answer this we need to know which part is it.
Pd(LDO)=4*85mA=0.34W
Thermal resistance of a TO-220 packages case-to-ambient is about 50°C/W to 60°C/W.
Tcase over ambient temp. =0.34*60=20°C
so for a 25°C room we get 25+20= 45°C case temp.
this can't be related to as truly "hot".
it doesn't pose any problem to the LDO and no heat-sink is actually required.
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