Misc Electronic Questions

[Billy Mayo]

I thought it was ringing also , but it's a switching power supply they call it ripple

The waveform decays like a damping effect

Does this waveform look normal to you for a switching power supply?

This is the main waveform that will be converted to DC by using a cap.

 

[KeepItSimpleStupid]

Generally, you would like to minimize ringing. There usually is some. That much may be excessive, but as you say it's converted to DC, so it may not matter.

You EZ-hook is too close to other interference sources. Not sure if they are EMI or RFI. In any event, you always want to cross the magnetic field lines perpendicular and not have any loops in your wire.

 

[Billy Mayo]

yes it looks like dc with noise ripple ripple on top, but its very small signal

I'm not sure what those IC chips do, can you explain what is going on in this circuit

There is two diodes D117, D119 that are feedback to change the PWM modulation signal to the U113 chip to regulate the output so the output is regulated

I'm not sure how this work

 

[Billy Mayo]

Here is a 555 time with a FET on the output, what is the FET used for? i see this a lot when used with a 555 timer, they use a MosFET on the output of the 555 timer but why?



RC network on the ground buss going to the Earth , this RC network is a common mode rejection RC network for the whole circuits ground , the RC network is on the ground buss connect with Earth

Have you seen this or heard of this?



Zener Diodes to protect over voltage for both positive and negative cycles, The zener diodes keeps the positive and negative cycles amplitude at a set limit

My manager said that the zener diodes are cancelling each other out, I'm not sure what he means by that

If the feedback resistor that is controlling the gain gets open or shorted it's still going to saturate the op amp with those zener diodes right?



Why did they use this PNP transistor? and not a NPN transistor? and will the base to emitter measure 0.7 volts?



Here is a couple more NPN transistor, will the base to emitter measure 0.7 volts?

 

[Billy Mayo]

Is this ground Impedance, my manager called it common mode reject the RC network of the whole circuits ground to earth

He says that it helps out with the potential difference and that the whole circuit is not floating

What does he mean by this?

 

[KeepItSimpleStupid]

The first 3. Need more time for the next 2.

1. Easy to interface. It's probably a logic FET. I can't see what the other end is connected to.
2. The Far end is a good AC ground, but poor DC ground. It's a decoupling circuit. That covers post #85, I think. manager is correct.
3. The zener diodes are bidirectional clamps at +-(Vz+0.6). They are better put in the feedback loop.

 

[Billy Mayo]

1. Easy to interface. It's probably a logic FET. I can't see what the other end is connected to.

Interface, do u mean the FET match the impedance or interfaces with the circuit and 555 timers output together better?

2. The Far end is a good AC ground, but poor DC ground. It's a decoupling circuit. That covers post #85, I think. manager is correct.

How would u do the DC ground better?

How do you tell what's an AC ground and what's an DC ground? the ground symbols look the same

Mostly I would see a parallel cap to ground , that's when I know it's an AC ground

3. The zener diodes are bidirectional clamps at +-(Vz+0.6). They are better put in the feedback loop.

Vz means the zeners voltage

Zeners voltage + 0.6 volts = what?

There bidirectional clamps , protect the op amp from what? if the feedback resistor opens or shorts the bidirectional clamps can't do much right? so what are they there for?

 

[Billy Mayo]

555 output with FET pictures




AND gates used as a Flip flop circuit, I don't know why the designer didn't use a Flip flop chip instead he used AND gates and wired them up like a flip flop IC chip

 

[kubeek]

Here is some switch power supply waveform's

What kind of switching power supply waveform's is this called?

It is called ringing. If you measuerd this with those foot long probes, then no wonder it looks like that. The ground of the probe needs to be as short as possible to minimize the inductance and get good high frequency response. Try measuring the same thing without the hook clip, only putting the pin on the probe to the signal and using the spring ground lead attached to the nearest ground point.

 

[Billy Mayo]

It is called ringing. If you measuerd this with those foot long probes, then no wonder it looks like that. The ground of the probe needs to be as short as possible to minimize the inductance and get good high frequency response. Try measuring the same thing without the hook clip, only putting the pin on the probe to the signal and using the spring ground lead attached to the nearest ground point.

Actually for that measurement I didn't use the Yellow Ez hook , so that is the waveform that goes to T100 and T102 and the output of T100 and T102 are that ringing waveform

The Cap 117, C118, C119, converts that High Frequency ringing waveform into a 25VDC

 

[Billy Mayo]

What state or mode is this transistor in? since it needs an input signal to turn it on and forward bias the base - emitter?

The transistor is off , not active , zero volts across base to emitter, no .7 volts

The input AC voltage will make the transistor active and turn on but it will still measure zero volts across the base to emitter right?

for Q2, it's less easy to determine whether other transistors have a permanent bias or not.

If a transistor is not permanent bias , it gets forward biased , active, turns on, energized from an input signal

Is the transistor a switch? or amplifier?

 

[kubeek]

Cap 117, C118, C119 in which picture?
Too many pictures, too many questions.

 

[Billy Mayo]

Permanent bias
0.7 volts from base to emitter as an amplifier
0.7 volts from base to emitter as a transistor switch?

Not Permanent bias
0 volts from base to emitter as a transistor amplifier
0 volts from base to emitter as a transistor switch
** Only gets forward biased 0.7 volts, active, turns on, energized the transistor from an input signal?

What is this called when the transistor is not forward bias except when the input signal is applied?

 

[KeepItSimpleStupid]

Interface, do u mean the FET match the impedance or interfaces with the circuit and 555 timers output together better?

No, just do a search for "LOGIC FETS". The Vgs turn-on voltage is compatable with TTL and they require little current to tun on. Also some CMOS IC's require levels very close to Vss and Vdd. Adding a diode drop is too much.

How would u do the DC ground better?

How do you tell what's an AC ground and what's an DC ground? the ground symbols look the same

Mostly I would see a parallel cap to ground , that's when I know it's an AC ground

Chassis and Earth have two different symbols. Generally, in most systems, Earth and protective ground and some internal grounds are tied together at one place. There are times, however where one might want a clean low-current ground. Usually inductors and a resistor are used.

What MIGHT be happening in your case, is that any AC transients are coupled through the capacitor. The resistor makes the other side a cleaner ground.

Ground is a very mysterious concept to many people. In a hospital and other sensitive facilities, you may have a green for ground and also a green with yellow stripe for ground. There are ORANGE receptacles that are used for devices that need an "isolated ground".
This is analogous to signal ground and Protective ground (Earth).

It really is the right way to do things, but imagine every outlet in your house having a separate breaker, just to have the proper ground. What happens now, if a parallel circuit of outlets gets hit, it may take out devices in that circuit. If every outlet had their own ground, the devices would be safer.

Vz means the zeners voltage Yes, say the zener is 12 V

Zeners voltage + 0.6 volts = what? [so 12 V + 0.6 V from the OTHER diode]

There bidirectional clamps , protect the op amp from what? if the feedback resistor opens or shorts the bidirectional clamps can't do much right? so what are they there for?

OK, this might be harder to explain. Lets go simpler. The unity gain OP amp. The input is applied to (+) and there is a wire from the output to (-). Maybe simple to understand. Maybe not. In any event, the OP amp tries to make the (-) input the same as the (+) input because of feedback. Easy enough.

Now let's only apply a (+) signal, but put a reversed biased (4V Zener diode) in the loop. So, instead of a wire from out to (-) we have this diode. When the output gets bigger than 4V, the zener will start to conduct. Any voltage below that will effectively pass through. So, the Op amp could see a +12 V signal and clamp it at 4V to be compatible with say the input to TTL logic.

The Back to Back zener diodes are clamps. Almost like a bidirectional TVS diode. Because the diodes are in series, there is an extra diode drop.

 

[KeepItSimpleStupid]

AND gates used as a Flip flop circuit, I don't know why the designer didn't use a Flip flop chip instead he used AND gates and wired them up like a flip flop IC chip

They didn't cost anything. Extra parts re-used.

PS: "The OP" is "The Original Poster"

 

[Billy Mayo]

So there is a difference between FET's and Logic FETS? they are two different things right?

The Back to Back zener diodes are clamps

so if the input signal is +12 volts and the back to back zener diodes are clamps at 4 volts
The input signal will only go up to 4 volts right?

Is the back to back zener diodes clamping the input voltage or output voltage?

How do you set the clamps voltage points?

 

[KeepItSimpleStupid]

Logic FETS just have lower full turn on voltages.

---

Here is a simple example: http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/opampvar3.html

The clamps are crude. Basically set by Vz. Back to back 4v zener diodes would clamp at + and - 4.6 V approximately. They clamp the fed back voltage. If they were on the output, they would dissipate power. Same for the input. These are in the feedback path. Hardly no current.

This is a very interesting part I ran across: http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/opampvar3.html

I've considered getting one to play with.

 

[Billy Mayo]

Logic FETS just have lower full turn on voltages.

You mean the FETS gate input threshold voltage is lower to turn on the FET?

So Q3 FET is on the output of the 555 timer, but what does it do, why use a Logic FET on the output of a 555 timer?

Does it Clean up the square waveform or sharpen the edges?

oh ok , So the voltage rating of the zener Diodes sets the clamp voltage

My manager said that since the diodes are in series but bi-directional is that they are cancelling each other out or they will cancel each other out because of the bi-directional configuration

 

[KeepItSimpleStupid]

555: I can't see where the side goes.

The Zener rating + 1 diode drop sets the clamp. You can even set them asymmetrical if you want.

 

[Billy Mayo]

Logic FET on the output of 555 pictures