## Posts Tagged ‘demand for current’

### Transistors – Voltage Regulation Part IV

Sunday, August 12th, 2012
We’ve all popped a circuit breaker sometime in our lives, often the result of making too heavy of an electrical demand in a single area of the house to which that circuit is dedicated.  Like when you’re making dinner and operating the microwave, toaster, mixer, blender, food processor, and television simultaneously.  The demand for current on a single circuit can be taxed to the max, causing it to pop the circuit breaker and requiring that trip to the electrical box to flip the switch back on.

Last time we began our discussion on unregulated power supplies and how they’re affected by power demands within their circuits.  Our schematic shows there are two basic aspects to the circuit, namely, its direct current source, or VDC,  and its internal resistance, RInternal.  Now let’s connect the power supply output terminals to an external supply circuit through which electrical current will be provided to peripheral devices, much like all the kitchen gadgets mentioned above.

## Figure 1

The external supply circuit shown in Figure 1 contains various electronic components, including electric relays, lights, and buzzers, and each of these has its own internal resistance.  Combined, their total resistance is RTotal, as shown in our schematic.

Current, notated as I, circulates through the power supply, through the external supply circuit, and then returns back to the power supply.  The current circulates because the voltage, VDC, pushes it through the circuit like pressure from a pump causes water to flow through a pipe.

RTotal and I can change, that is, increase or decrease, depending on how many components the microprocessor has turned on or off within the external supply circuit at any given time.  When RTotal increases, electrical current, I, decreases.  When RTotal decreases, electrical current I increases.

Next time we’ll continue our discussion on Ohm’s Law, introduced last week, to show how the static effect of RInternal  interacts with the changing resistance present in RTotal to adversely affect an unregulated power supply’s output voltage.

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