I made a circuit I'm going to use in my car which is supplied through a 7805. The input voltage is as high as 14V sometimes and the current it has to deliver goes near 250-300mA. The heatsink reaches 60°C and it is in a closed and tight environment.
Is this safe for the circuit, including the board the heatsink is fixed to and all the wires around it (considering that this temperature could climb when in practical use)?
I think it's not an optimal design.
Most of your system power will be consumed by the 7805.
You have 14 V at the input? The 7805 will consume (14 - 5) * 300 = 2700 mW.
The output will be 5V / 300 mA, so you will get only 1500 mW. It will result in
about 30 % power efficiency.
You should use a DC/DC converter chip in which case you can easily have
a power efficiency of 90 ~ 95%. Among the other advantages: you need a
smaller transformer because you will not consume the difference, but transform
the difference.
It will never get hot.
It's better for the planet.
Dora
velson said:
Hi,
I made a circuit I'm going to use in my car which is supplied through a 7805. The input voltage is as high as 14V sometimes and the current it has to deliver goes near 250-300mA. The heatsink reaches 60°C and it is in a closed and tight environment.
Is this safe for the circuit, including the board the heatsink is fixed to and all the wires around it (considering that this temperature could climb when in practical use)?
I'm not very sure that switching power supply would do good in circuits with microcontrollers in them. Isn't there too much noise or interference in such supplies?
don't worry , use the 7805 with a little heatsink , 2x2 centimeters aluminum 2 mm thick will be enough.
I have in the car a 7805 working with a PC cd recorder that is rated 5 volts 0,55 amp. and works very well for hours.
Switching power supplies are used in ALL today's portable devices. The frequency
range of the switing is a few hundreds of kHz ~ 1++ MHz. If you add a serial
coil and a parallel cap at the output, you get basically no noise. Or in other
words, the noise (on the power line) generated by the microcontroller itself
is a lot higher than the one of the power supply -> Separate analog and digital
power and that should do it.
Dora
velson said:
Thanks for the reply.
I'm not very sure that switching power supply would do good in circuits with microcontrollers in them. Isn't there too much noise or interference in such supplies?
its not just very quick to get an smps supply..either you need to go in search for a suitable one or u need to deisgn onde yourself,but again you will need to run for finding the IC,s transformers etc etc.
whereas 7805 is just a plug and use type.
dropping 9V across is not a critical issue as the part istelf is designed for max 40V input ,provided adequate heat sink is provided.so as someone said above,use the heat sink and try to create some ventilation on board for air circulation.. and go ahead..it just works !!!
Hi
few years ago same situation with me. the circuit was ok in lab testing on even 14-15 Volts but heat up in car.
this due to the high voltage spikes produced by the car generator.
this heat is greatly reduced by using LC filter, normally used with car radio to filter out the spikes.
Use of SMPS and C to DC converters are also good options but i think this one is easier.
its not just very quick to get an smps supply..either you need to go in search for a suitable one or u need to deisgn onde yourself,but again you will need to run for finding the IC,s transformers etc etc.
whereas 7805 is just a plug and use type.
-cheers
LM2575 is also a plug and use type... you use 7805 because you never used a smps ic..
today you only have to add a diode and an inductor to the circuit and it works.
far better less heat problems, less heat means very more reliable along time
you have to design a complex smps if you plan to go from 110 or 220v ac to 12vdc for example. this one is complex. but really not one from 12v to 5v dc
and I repeat myself : very more reliable !
just have a try, dont affirm something without knowing because you didnt even try it !