12DC Sockets

[Muttley600]

ok, zener holds votage, if the current drops the zener won't work, so if I was to run 1A through a resitor it would hold it at 5v

just need to check what happens when I up the voltage, back in a mo

so, 13.7V with 7ohm load (1A) with R1 as 4.7K resistor = 6.03V
so putting voltage up to 35V moves it to 7.37V

so can we use/practise a zener that would show me how it holds spikes off for my project

Here you are, sorry I was getting carried away playing

**broken link removed**

so what happens if voltage spike got to say 200v, would the zener just break down & give up/shut down, have they got an arc over voltage

 

[cowboybob]

And even less current (down to 50Ma or so) will give you the 5v.

 

[Muttley600]

And even less current (down to 50Ma or so) will give you the 5v.

I was just trying to relate it to a voltage spike

edit: how do these stop voltage spikes or am I confusing things here, you've got my mind back on my project now **broken link removed**

just looked back, you were on about using a zener to shut circuit down in the case of spikes, what was that TVS diode KISS was on about, he said each would clamp pos & neg spikes, which way around **broken link removed** & I'm presumimg clamp means holds them before they do any harm, is that without shutting circuit down or same thing

so why would you need a 5v reg like I brought when you could just set up a 5V/2A max supply with a zenner **broken link removed**

sorry about all the Q's

so using this zener: a 2A max load with a 3.6ohm resistor would keep a steady 5V, let me go an change load, so if load changed to 1A it would mean voltage of 6.26 - is that acceptable for a 5V gadget like a phone or camera **broken link removed**

now, we have the other question, what is a 3.6ohm resistor, is that a 3.6k resistor

 

[cowboybob]

I'm sending a revised schematic by email. It will be better configured for demonstrating what's going on with the circuit.

I would suggest you keep it original and make a copy it with an altered file name, just in case the copy gets wangered somehow.

Them if need be, we can revert to the original.

 

[Muttley600]

As if I could mess it up :-/
Back on phone for a bit
What is the schematic of then as I'll be off computer for about an hour?

 

[cowboybob]

so what happens if voltage spike got to say 200v, would the zener just break down & give up/shut down, have they got an arc over voltage

a zener is not meant to be a "spike" protector. It is meant to be (and works as) an over-voltage controller. Thats means that. within defined limits (fairly tight) the zener can keep an output voltage pretty constant. But below a certain limit, it fails to maintain that constant. Above those certain limits and it fails catastrophically (dies).

You should have the new schematic at your doorstep now.

 

[KeepItSimpleStupid]

Schematic:

I think it looks basically like a multivibrator, recifier, capacitor filter where T3 turns off the free-running oscillator providing regulation.

With ZD1 being a regular diode, nothing much will happen.

I would suggest severing the connections: C of T3 and remove R5 to see if it oscillates and creates an unregulated output.
You might need to provide some series resistance for the choke too. Measure it with an ohmmeter.

In the long run, you could consider one of the low parts count regulators for automotive applications.

There is one glitch when supplying power to USB devices and that's providing the proper signature for the available charing current, otherwise it's limited to 100 mA. Some of this info is hard to find. For example there are two resistors in the USB cable for Motorola cell phones so it can charge at the higher rate. 2A is required for the Ipad, but the USB spec really doesn't allow that much current.

 

[cowboybob]

THAT's the kind of input we were looking for!!

I'm gonna mash the "+" button 50 times.


Oops, only get one mash. well I was gonna do 50...

You's a good man, KISS.

 

[Muttley600]

a zener is not meant to be a "spike" protector. It is meant to be (and works as) an over-voltage controller. Thats means that. within defined limits (fairly tight) the zener can keep an output voltage pretty constant. But below a certain limit, it fails to maintain that constant. Above those certain limits and it fails catastrophically (dies).

You should have the new schematic at your doorstep now.

Got your file thanks CBB
When you say it fails to maintain that constant, does it really matter if voltage low, wouldn't objects just shut down to lack of power
Above the limits, when you say it dies, as in burns out - not usable?

When I meant a spike, I was meaning voltage spike, looking back you were on about one running alongside the main supply line with it cutting fuse if spike happened

 

[Muttley600]

Think I'll let CBB play with changes to start with, but this in itself has raised more questions
KISS, when you say: There is one glitch when supplying power to USB devices and that's providing the proper signature for the available charing current, otherwise it's limited to 100 mA.
Does that mean each USB device needs specific current, I thought a device would only draw the actual current needed, hence me buying a 5V/3A reg to run my camera/charge phone via two sockets off same reg, am I getting confused

So far my idea of supplying power sockets that can run one or five sockets off 12V seems reasonable but where does this leave my 5V devices?

 

[KeepItSimpleStupid]

A note about zener diodes. One is there are two breakdown mechanisms, one called Zener and one called avalanche. It turns out that they both occur at 5.1 V which makes that particular voltage special.

The breakdown voltage is optimized for the zener diode. So the PRV (Peak Reverse Voltage) value is controlled.

Exceeding the PRV is non-destructive. It won't "break" the diode permanently. It will, however not function properly.

A TVS diode is Zener diode optimized for spike/surge suppression. They have a much larger body.

You can use Zener diodes in series to get different voltages because the voltages will add.

While we are on the subject of diodes:
Regular diodes (especially back to back) are sometimes used to clamp voltages to +-0.2 or +-0.6 volts.
Solid state high voltage rectifiers are essentially lots of regular diodes in series. Thes could easily have a 10 V forward drop rather than the typical 0.6 V. The 0.6 V drop is temperature dependent. About 10 mV per degree C. Some designs use 0.7. Shotkey diodes are around 0.2 volts.

When using diodes at low currents, it prudent to check the data sheets.

 

[Muttley600]

New test:
8V = 4.52V / 53.61mA
10V = 4.92V / 78.11mA
12V = 5.13V / 105.62mA
18V = 5.46V / 192.98mA
24V = 5.63 / 282.58mA
even pushing it to 100V is only 6.42V, that seems sensible & when were talking mA, this is minute really isn't it = 1.44A off 100V

 

[Muttley600]

ok, I'm a bit lost right now

**broken link removed** what type are we looking at?

Zeners are different *read double confused now*

**broken link removed**

**broken link removed**

at least I can nose at datasheets

CBB what type are you on about, help KISS is speaking a different lanuguage, can you translate **broken link removed**

did all this seem too much to take in while you were learning **broken link removed**

 

[KeepItSimpleStupid]

Avalanche and ener breakdown: **broken link removed**

Some of what I said shows up in Solid State Physics where you look at how devices are made.

TVS diodes are available as Unidirectional and Bi-directional. Meaning I could get one that would clamp at +-100 V.

I did mention that diodes are sometimes used back to back, or an anti-parallel configuration meaning one diode faces the opposite direction. If these were regular diodes, then the clamp would be a +-0.6 Volts. If they were zeners, then the Zener voltage of one and the Zener voltage of the other in the opposite direction.

 

[cowboybob]

When I meant a spike, I was meaning voltage spike, looking back you were on about one running alongside the main supply line with it cutting fuse if spike happened

Don't remember that (not surprising) but there is a device for that (Voltage spikes) called MOVs (metal oxide varistors) that a certain over-voltage level, short the mains power to ground (and then blow a fuse or trip a breaker). That's all a MOV can do. And, of course, it dies in the process, and must then be replaced.

When you say it (the zener, my edit) fails to maintain that constant, does it really matter if voltage low, wouldn't objects just shut down to lack of power

NOTE: A zener in never in a circuit without a resistor (R) (or resistance in some manner) in series with it.

If you were to put a voltmeter across (that is, one lead of the meter on one side of the resistor [that is in series with the zener] and the other lead on the other side of that resistor) you'd see that as you increased the supply voltage, the voltage across the zener would stay essentially the same, while the voltage across the resistor would go up by the amount the supply voltage had gone up.

It is this resistor/zener circuit that "bleeds off" excess voltage by the increased current running through it, caused by the zener's automatically decreasing it's internal resistance (R) to maintain a constant voltage (E) across itself. The excess current now runs through the fixed resistor as well, thereby increasing the voltage across it, (bleeding it off).

Again, the zener (at least as far as I've ever used them) isn't really designed for supplying a constant voltage (as apposed to current) to anything other than another component/circuit in a larger array of components. It's used to maintain a constant voltage, most often as a bias on a component, like the base of a transistor, so that it will respond to other circuit stimuli in a predictable manner. Something else in the larger circuit (like the power supplying the entire circuit) might vary to some degree for some reason, and the zener counters that effect by maintaining a constant voltage.

And so, in a sense, with input voltages too low, other "objects" (components in the circuit) will shut down or not perform as expected and the entire circuit would then fail to perform optimally or at all, depending. And, of course, with input voltage too high, the zener can (and will) fail, rendering the entire circuit unusable and possibly damaging other components in the process.

I know all this is difficult. That's why the sims. By making changes to the circuit, one at a time and then seeing the resulting values, you'll be able to grasp what the zener is doing.

Nobody said it ain't confusing. It is. But by being methodical with your testing, you'll get it. An if not, we'll just keep plugggin' till you do.

CBB

 

[KeepItSimpleStupid]

A TVS diode is a specialized Zener. It COULD be in a circuit without a resistor unless you want to call the fuse a resistor.

 

[Muttley600]

ok, I've had a smoke & calmed down, it's just cause I don't understand it AT the moment, let me try & decipher this & see how I get on **broken link removed**

A note about zener diodes. One is there are two breakdown mechanisms, one called Zener and one called avalanche.

I thought breakdown when something had enough power to arc across & carry on, this isn't the only type of breakdown is it

It turns out that they both occur at 5.1 V which makes that particular voltage special.

Can you explain these two differences so I can understand this bit

The breakdown voltage is optimized for the zener diode. So the PRV (Peak Reverse Voltage) value is controlled.

Exceeding the PRV is non-destructive. It won't "break" the diode permanently. It will, however not function properly.

So if you exceed the PRV you need to replace it in simple terms

A TVS diode is Zener diode optimized for spike/surge suppression. They have a much larger body.

Will this control neg & pos spikes then **broken link removed**

You can use Zener diodes in series to get different voltages because the voltages will add.

I understand that bit, sad I know

While we are on the subject of diodes:
Regular diodes (especially back to back) are sometimes used to clamp voltages to +-0.2 or +-0.6 volts.

Does that mean you can pin a voltage right down if you know the load, having a varying load would be harder?

Solid state high voltage rectifiers are essentially lots of regular diodes in series. Thes could easily have a 10 V forward drop rather than the typical 0.6 V. The 0.6 V drop is temperature dependent. About 10 mV per degree C. Some designs use 0.7. Shotkey diodes are around 0.2 volts.

ok, lets do diodes before moving onto rectifiers **broken link removed**

When using diodes at low currents, it prudent to check the data sheets.

Datasheets are good, it saves guessing what I'm talking about **broken link removed**

ok, so I did bad, but at least I'm trying to learn

 

[KeepItSimpleStupid]

Here is a TVS diode datasheet: https://www.electro-tech-online.com/custompdfs/2012/02/PESDXL1BA_SER.pdf

 

[KeepItSimpleStupid]

Breakdown, an example:

Suppose you had a spark gap. Nothing but electrodes in air. It's "BREAKDOWN" depends on the dialectric constant of air and the spacing. So, once it breaks down it acts as a short and there is no damage. I'm not saying it's the same mechanism, but it's the idea that counts. The fact that no damage occurs.

 

[Muttley600]

Ok, I have read up on breakdowns thanks to KISS's link, so in order to prevent a breakdown we have to read data sheet & make sure we keep diodes cool or stay away from the parameters/edges of breakdown V.

& still a page to read on here.lol

Back to it tomorrow, goodnight both
Best Regards
Graham