designing a power supply for a electronic ciruit

Amperage.

Physically an amp is a flow of a few trillion negative particles of the atom called electrons on a light speed scale. The standard metric system prefix mill lee ( mili- ) for a thousandth denotes milliamps. 250mA is a quarter amp, 500 is a half and 750 is three quarters of the latter.

The huge rechargeable torch cells ( or batteries if you like ) have a current supply of up to 5A supply for about an hour called an amp hour ratting in this case a 5Ah. Any more drain the voltage will drop loosing power.

Throw away smaller ones are 50mAh ratings lasting 50 hours at a current drain of a mA. At their amp hour ratting should last an hour. Over the ratting the voltage drops loosing power.

Voltage.

It doesn't flow, only a live electrical energy each end of every source. One end is marked with a red cross for the positive terminal and the other not marked ( or with a dash ) the negative terminal. You can feel the voltage when you bring together the terminals of two torch batteries less than a millimeter gap slightly moving side to side.

Never try this with powerful automotive batteries. They are far to powerful for that sort of thing. There is a potential accidental shorting. The current supply can spark like fireworks with as much amperage as several tens of amps. A fully charged battery is so powerful they can weld but discharged low in a few minutes.

In physics voltage is a store of excess electrons making a battery terminal some what domineeringly negative. The other end is an equal lack of electrons making that terminal some what domineeringly positive.

When a load ( Any electronic device or circuit ) is connected is always in parallel ( across the two opposing voltages ) the negative electrons repelled by the negative voltage and attracted by the positive voltage where current flows. This is known as the electron current flow direction in one steady direct stream called direct current.

Wattage.

Taking a 1.5V torch battery if we muiltiply the amp hour ratting by the voltage gives the power ratting. For example 1.5V multiplied by a 50mA ratting pans out to 750mW source. The power drain is similar to the current drain. It will supply 1.5V at a current drain of 50mA supplying a power of 750mW in an hour or 50 hours at a current of 1mA respectively. The same voltage low power consumption is low current drain and high power supply high current.

Ohms. 

When a load is loaded ( always in parallel ) across any DC source draws a current resulting in the power drain on the source. The conductance is in the resistance of the load in Ohms. A 1.5 ohms resistance will draw up to 1.5A from a powerful touch battery but will be a dead short for budge smaller ones.

A big rechargeable 1.5 torch cell with a load of 1.5 Ohms circuit will draw it's amp hour rating in terms of it's wattage. Knowing the amp hour rating multiplied by the voltage gives the equivalent of ohms in parallel with the battery. It applies knowing the total current drain of any voltage too.

Electrical engineers designing electronic circuits start with the power output requirements working out the power drain of the required power output that determines the power supply ratting of the circuit or device required. For audio circuits the total power drain from the source under the load  maximum volume.

The voltage is not critical chosen mainly based on economy and convince. It is the in power output choice under the maximum load conditions of the circuit or device in mind in ohms using ohms law formulae though an equivalent resistance in parallel with the source. Knowing the maximum power out of the load required we can deduce the maximum current drain requirements from any convenient voltage in mind.

For example a maximum of 5w required from a robot will require a DC power supply arrangement choosing say four 1.5V touch batteries for economy sake is 6 divide 5 giving a maximum current supply of 1.2A the amp hour ratting of the source. The robot should drain the batteries flat in an hour at that current drain. 

If we double the touch battery arrangement using the highest Ah ratting possible ( about 5A ) we have a DC power supply arrangement of 12 times 5 giving a wattage supply for 60W robot for an hour.

Four 1.5v 100mAh ratting torch batteries arranged in series makes a 6V 100mA source is a minimal power supply for building effective electric toy electric cranes for the little ones. There is enough power to teach them the basics of electricity and magnetism relationship.

The same four batteries arranged in parallel make one 1.5v 600mA source because the circuit is shearing the same voltage of all the batteries shearing the current drain between them. The expensive big 1.5V rechargeable batteries in series makes a powerful 6V, 5Ah ratting. The source will last an hour at a power supply of 30W. A 20W audio amplifier design at full volume is capable of up to a loud rock band volume for an hour.

The power drain of audio amplifiers depends on the volume. At minimal volume of about an amp or so should last 20 hours. The wattages pans out to 20W of power drain at minimum volume and 40W at full volume. The audio amplifier power supply specifications is drawn upon the full volume loudness aimed for.

Thus in choosing a power supply arrangement depends on the maximum power drain demand of the load in mind in the required lasting time of the battery. We work from the maximum wattage required at any voltage arrangement calculating the equivalent power drain of the load at full power drain of maximum power out of a device like a robot.

The current drain drawn from any source is relatively unstable. The device, or robot will perform erratically and unpredictable. The power output will wax and wan terribly.

A solution is an electronic circuit that stabilizes the voltage. The current supply is still a bit unstable so it's common both the current and voltage is stabilized in the same circuit. When the voltage is stabilized with a voltage stabilizer circuit another circuit a the output is designed as a current stabilizer is added.

When both voltage and current is stabilized the circuit, device, robot video or audio amplifiers will perform admirably. The stabilized circuitry is aimed to stabiles the constant lowering of power drain from the battery source.