Opamp power supply

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Hello All,
When designing a power supply for an opamp that requires + / - 15V at 5mA. Obviously the voltage doesn’t alter however would I be correct in saying for one opamp you would require just 5mA for two 10mA for three 15mA and so on… or does it operated the same way as voltage rails, (e.g.: remains the same)

I apologize if this seems very basic however I am new to electronics and any help would be appreciated

Thanks…
 
You must also add some for all passive parts like resistors which act like different kinds of loads and of course the real load. Don't forget that 78xx regulators themselves consumes power, see datasheet for this but it is a couple of milliamps. Notice also that 78xx and especially 79xx must have a minimum load in order to work. Too small load you will get more voltage out!
 
Hi,
opamps are usually ClassAB. The current quoted is nearly always the operating current for zero output current.
You should add at least 100% of output current +5mA.
Remember to allow for current in the feedback loop and an allowance for peak current into non resistive loads.
Your requirement for a single could now be 40ma and a dual 75ma.
Add in local decoupling.
 
The opamp itself regulates its own current, so there is no need to worry about too much current. As mentioned you must give it access to more - given by the power supply. So make your power supply to give around 10 times as much as you think it will use, then you are safe. Because the opamp will use more power, if the output of the opamp is connected to a low impedance/resistance and the signal swing is high. Calculations via Ohms law: U=R*I and P=U*I.
 
sivan_and said:
:WRONG
For Linear regulators no min load is required!!!

For a 317 the setting resistors usually supply adequate load, but if you use high values for some reason you may need to ensure a minimum load for optimum regulation. See NS datasheet p2.
Since the regulator is floating, all the quiescent current must be absorbed by the load. With too light of a load, regulation is impaired. Usually, a 5 mA programming current is sufficient; however, worst case minimum load for commercial grade parts requires a minimum load of 10 mA. The minimum load current can be compared to the quiescent current of standard regulators.

edit: woops - missed the answers on p2 pf the thread... :eek:
 
Used 78XX/79XX decades ago..w/o refering data sheets:D
Only thing known at that time was max o/p current and max input voltage..Was a school student then...explaned the need for voltage stablising to a salesman shop selling components..he gave me a small circuit with a couple of capacitors and said to limit load current to less than 1 amp....
 
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