Various Electronic Analysis Questions

[BradtheRad]

What makes it go below the zero point into a negative cycle? is it because the resistance sets up a DC offset at the NODE point?

I think I see what you're getting at. Yes, if there were a plain wire between the cap and ground, the node would naturally be at ground (0 V).

However because the resistor is present, it allows the polarity on the capacitor to dominate. Notice the cap acts like a battery as it discharges. Its positive end being electrically closer to ground (0V), therefore the negative end creates a negative volt level.

Another way of seeing it, is that current flowing through the resistor creates a voltage on it. It is negative in this case because the current is flowing AWAY FROM ground (0V).

This should be very easy to see if you watched the animated simulation (linked in my post #19).

And if the resistor were not present, the capacitor's negative end would create several volts of negative polarity at the next device's input, which risks damage to the device.

 

[danny davis]

Thanks for your info.

The purpose might be to time-align one signal with another elsewhere, or eliminate jittery pulses, or to create a time-window of a certain length

Can you talk more detail about how the RC network time aligns signals, eliminate jittery pulses or create a time window? for what and how used?

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When I'm troubleshooting a short , there is components that will measure a short, making the DVM meter BEEP, but when I take out the component out of circuit it will measure FINE

In circuit the component will measure a short and make my DVM meter BEEP

So What is this called? a false short? or ghost short? a false continuity or ghost continuity

And why does the GOOD component make my DVM meter BEEP and have a shorted Continuity? is it because the GOOD component is in parallel or in series with the short?

 

[danny davis]

At work we had to changed out 12 volt regulators with another 12 volt regulator because of a IN RUSH current problem

I don't understand what's the difference between IN RUSH current and a LOAD , because the current goes up and the voltage goes down

If you load the regulator to much the current goes up and the voltage goes down

If the IN RUSH current it high on the output of the regulator the voltage goes down

So the IN RUSH current is loading the regulator? but how is it different than a LOAD?

It's a 12 volt regulator at 1 amp, they switched it with a different company that is the same 12 volt at 1 amp, my manager said that the internally the regulator must of had a bad feedback loop internally because the regulator was current limiting and not the new one which is rated the same voltage and current output

What is it internally in the regulator that can cause current limiting? both regulators have the same voltage and current output but one current limits and drops the voltage in half

It goes from 12 volts to 6 volts as more current is draw by the regulator

 

[BradtheRad]

Can you talk more detail about how the RC network time aligns signals, eliminate jittery pulses or create a time window? for what and how used?

These are quick and general descriptions of a few of the ways capacitors (and coils) can be used in circuits. They are an easy way to introduce time-related behavior.

Someone ought to produce a book of 1,000 circuits, showing the various roles for capacitors. What they can do, by themselves and in combination with simple components (for instance, your schematics posted in this thread).

Til then, however, it appears we must compile our own encyclopedia in our mind.

The diode-capacitor-resistor combinations can be arranged every which way. They can delay a pulse, extend a pulse, shorten a pulse, etc.

A bit of experimentation will repay your efforts.

 

[danny davis]

They can delay a pulse, extend a pulse, shorten a pulse

Yes I have seen these in logic circuits

They wave shape the pulse

 

[BradtheRad]

At work we had to changed out 12 volt regulators with another 12 volt regulator because of a IN RUSH current problem

I don't understand what's the difference between IN RUSH current and a LOAD , because the current goes up and the voltage goes down

If you load the regulator to much the current goes up and the voltage goes down

If the IN RUSH current it high on the output of the regulator the voltage goes down

So the IN RUSH current is loading the regulator? but how is it different than a LOAD?

It's a 12 volt regulator at 1 amp, they switched it with a different company that is the same 12 volt at 1 amp, my manager said that the internally the regulator must of had a bad feedback loop internally because the regulator was current limiting and not the new one which is rated the same voltage and current output

What is it internally in the regulator that can cause current limiting? both regulators have the same voltage and current output but one current limits and drops the voltage in half

It goes from 12 volts to 6 volts as more current is draw by the regulator

Inrush current happens at power up. Generally it is due to capacitors charging from 0V. This makes them look like a very low ohm resistance, at first.

The startup surge can weaken or destroy components if they are not able to handle the current..

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When I'm troubleshooting a short , there is components that will measure a short, making the DVM meter BEEP, but when I take out the component out of circuit it will measure FINE

In circuit the component will measure a short and make my DVM meter BEEP

So What is this called? a false short? or ghost short? a false continuity or ghost continuity

And why does the GOOD component make my DVM meter BEEP and have a shorted Continuity? is it because the GOOD component is in parallel or in series with the short?

When you hook up your meter leads to a component in circuit, you are testing the other components too.

That is why you must often test a component 'out of circuit'. You must clip one lead to disconnect it.

 

[danny davis]

When you hook up your meter leads to a component in circuit, you are testing the other components too.

Yes RIGHT

What I'm saying is that if one of the components is SHORTED , it will make the other components measure a SHORT also in circuit, so you have to Disconnect a LEG from each component in the area unit you find which component is the real short

That's what I have been doing lately

 

[danny davis]

Today at work I have noticed that when One Decoupling cap is backwards it will pull down the Rail voltage, why does it pull down the DC buss rail voltage

They have multiple Decoupling Caps from Vcc to Ground, if one of the Electrolytic Capacitor is put in Backwards it will pull down the VCC to a lower voltage

12vdc VCC, if one of the decoupling caps is put in backwards it will pull it down to 10 volts or lower , but why?

When an Electrolytic capacitor is in backwards it acts like a short or open?