# How simple circuits are connected together to form complex circuit, without changing their own funct

#### xxxyyyba

Joined Aug 7, 2012
289
Here is one quote:"The basic process used to make all electronic circuits breaks down into a sequence of combinations. First, the individual components (resistors, capacitors, diodes, and so on) combine to form simple circuits. Then, simple circuits combine to make more complex circuits. After that, complex circuits combine to form complete devices".
There is also example of one complex circuit, which consists of few simpler circuits connected in cascade.
Although this concept of combining simple circuits to get some complex circuit sounds very logical, there is one problem. Every simple circuit which would be used (combined with other simple circuits) to form complex circuit has some function: how can we know that after connecting simple circuits together, function of these simple circuits would not change? Are there some conditions that must be met in order for this strategy (look at quote) to work? It looks to me that in general this strategy would not work. I used google to find answer and I think that my question has something with "Loading effect" but I'm not sure.

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#### SLK001

Joined Nov 29, 2011
1,548
You design the individual simple circuits with the "loading effects" taken into account. When done properly, cookie cutter complex systems are fairly easy.

#### wayneh

Joined Sep 9, 2010
17,262
Right, it comes down to the specifications, in and out. It can be very modular as long as the pieces are chosen to perform within the specifications.

One thing that adds huge complexity is when all the various modules are placed under control of a central processor. I'm thinking a of a TV I worked on a while back. The CPU ran and monitored the power supplies, managed the start-up sequence and on and on. But individual functions like power supply, audio amplifier, and so on looked a lot like you find anywhere else.

#### #12

Joined Nov 30, 2010
18,224
The primary concern is that each simple circuit has the voltage and current capability to drive the next module. If you need a milliamp of current, that's what you design your simple circuit to do. If you need an amp to drive the next stage, that's what you design it to do. Most analog design work starts at the output and works backwards. Fifty watts to drive the speakers? Fine. Design a 50 watt output stage. Now, what does it need for a driver? Five volts peak to peak at 100 milliamps? Fine design one of those. Connecting them together doesn't turn a moose into a mouse.

#### hobbyist

Joined Aug 10, 2008
892
Hi, I just did a video series consisting of 4 videos on my utube channel, called "design steps torque conv. circuit" .

I like sharing how transistor circuits can be designed simple or complex, at a hobby level,

I did this video series mainly to show, other hobbyists in this field, how to design a complex circuit, by building one stage at a time to accomplish a certain task. Then combining each stage together to get a completed functioning circuit.

In the video series I was experimenting with using all transistors, to design a crude motor control, that would have the ability to sense a change in motor voltage due to loading, and feedback a current to ramp up the voltage applied to the motor. Hence my version of torque controle.

In the series I start out with making a simple classic transistor , series feedback voltage regulator, to drive a toy DC motor, then I explain how I need to make changes to it by adding different stages to combine with it, so I can eventually have a change in motor current be detected, and fedback to the regulator, and the regulator would increase power output to the motor via, other circuit stages. I explain in detail what components to choose, as well as values for biasing resistors, all this was designed using the very basics of circuit analysis.

you can find this video series at this link:

yes I know that realworld electronic motor controls are PWM, I'm now doing a video series on that as I learn through experimenting, so as to upgrade my homemade motor control for my minilathe to PWM, with feedback.
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#### BobaMosfet

Joined Jul 1, 2009
2,073