Leftyretro
New Member
Hi
sorry to dig up an old thread, but i just have a quick question and this is very relevent - I am building a relay box/power supply/square wave generator.
I plan on having 230v IEC mains plug on the back, through a fuse, transformer to 15v, bridge rectifier (with the filter caps earlier in the thread).
Now on to the question, I want to have a 7805 drawing 200mA, a 7805 capable of drawing 1A, and a 7812 capable of drawing 1A.
What size of capacitor would be suitable to use as the storage cap (the one that goes after the rectifier before the regulator. I have a few 2200uF and a few 4700uF. would any of these (or a combination) be suitable for this, if not what would?
The load on 1 of the 7805's and the 7812 may be switched on and off regularly.
I have all the smaller caps for use with the regulators.
Thanks
a single 2200uF should work fine, but a single 4700uF would be OK also, any more would be over kill and just take up more space. All the input filter needs to do is to keep the lowest peak of the input ripple voltage above the minimum input DC voltage specification for the regulators.
Your biggest problem will be the size of heat sink you will need, certainly for the 7805 that will be supplying 1 amp. That one has to dissipate 10 watts of heat which is a whole lot of heat. You might want to put a series power resistor in front of that 7805 such that the input voltage is closer to the 9-10volt range when supplying a one amp load.
Lefty
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