Redução de tensão para alimentar CIs - Eletrônica - Clube do Hardware

I need to reduce 312VDC to 12VDC and 65mA

40mA is used to provide the nominal current of the 12V Zener diode,

25mA can power CI (or base of low gain transistor... I have not decided yet)

How can this be done?

I only have 1/4W resistor and VCE transistor max 60V

The DC-DC converter cannot be used as a solution because, ironically, the circuit is used as a power source

Yesterday they were talking about mobile phone chargers. I released this charger solution, and I modified it to output 12V instead of 5V:

I don't understand the purpose of your project, can you explain it better?

At constant power (in this case, the maximum value is 1/4 W), the resistance increases with the square of the voltage. At high voltages, high resistance is required (for example, for 1/4 W and 300 V, you have 360kΩ)

.

When answering your question, connect several transistors in series so that the collector-emitter voltage (maximum 60 V) of each transistor supports 312 V input together. These transistors are then activated through the high resistance voltage divider through the base in the emitter follower configuration.

This is a bad type of voltage regulation, but it works! I suggest you try to adjust the value through computer simulation.

Hope this helps

I think q is 311V continuous and it is difficult to reduce it. The only way to reduce it is to use a large resistor (if the power consumption is constant). I think if you want to use 220v AC voltage to supply 12v 65mah power supply, it is more practical and easier than using capacitors and reactances to reduce the voltage. If you want to publish the model, I'm ready to prepare it here from that source (copy from the tablet).

Or make the switching source equal to 

suggested

I want to do two things:

One with PWM

Another linear adjustment

So I mentioned one for CI (555) and the other for transistor (MJE13003)

In the sketch I wrote, I circled the area where the thing I was asking about turned red. She is the bottleneck.

I like the idea of ​​using transistors to reduce the voltage from 60 to 60

But it will be a mess

As KeVTaG suggested, one of them will have a capacitor. The problem is to use Zener diodes to regulate all the current through the capacitor. So the transistor. The MJE13003 can handle 600V.

As shown in the picture, it will not be Darlington. But don't be Darlington, you need a 25mA reference current.

Why do you want such an uninsulated source?

As I imagined, it shocked the exit.

The first circuit is possible, you don't even need a transistor. To use a 1.5uF capacitor, just connect a 1W Zener tube with a 100R-1 / 4W resistor in series.

The second circuit does not work, all you can do is burn everything. It is completely impossible to use a transistor to reduce the PWM voltage to 300V.

Here, the schematic diagram of the plate q triggered the relay I copied. It is indeed very simple. There are 220 alternating currents and a voltage of 24V is left for the relay. I believe that changing the Zener diode to 12V does not require replacing the capacitor.

  I don’t know much about calculations, but I saw a 220k resistor in the source circuit of an industrial machine to reduce the voltage from 311V to 12 or 13v, which is another 100uF capacitor between UC3844 or UC3845 and Vcc and gnd powered by. UC. Then, when you turn on the power, the resistor will start at the UC38xx (or any other switching IC), and then this IC will generate PWM and power the rest of the board. But there is a defect where there is no connection on the board. Sometimes I just replaced the power capacitor of UC38xx, and then the card can work again. But with such configuration items, I find it easier.

When I needed to replace the relay with the 220V coil in the freezer, I used it there. At that time, I had several relays with 12V coils available, so I adopted this solution.

I don’t know much about calculations, but I see that 220k resistors in the power supply circuits of industrial machines are used to reduce the voltage from 311V to 12 or 13v to provide power for the UC3844

Or another 100uF capacitor between UC3845 and Vcc and UC gnd. Then, when you turn on the power, the resistor will start at the UC38xx (or any other switching IC), and then this IC will generate PWM and power the rest of the board. But there is a defect where there is no connection on the board. Sometimes I just replaced the power capacitor of UC38xx, and then the card can work again. But with such configuration items, I find it easier.

This CI type was developed for assembling switching power supplies, and it is very similar to the famous STR5XXX in TVs.

No escape, the call to them is the same.

As for advice to friends

There is no point in reinventing the wheel. Speaking of power supplies, we have switches, traditional switches with transformers and capacitors that are not recommended, because if the current is high and their efficiency is low, they have no insulation and waste energy.

Whether the resistance is suitable for a voltage above 30V, its heat dissipation is very large.

day!

I made a serious mistake before:

The red areas I want to circle

I know the things in the picture immediately become toast

Other components may not be in the final value. This is just a sketch

"It makes no sense to reinvent the wheel

This is what i want

, For many reasons:

Innovation/learning; using components I own (very popular); I don’t like transformers...

Sometimes I want to learn oscillators that use only passive components.

I think our master’s first number (mobile phone charger) will solve this problem.

But first I want to get these two types here

I stick to this design. I think this is very elegant. At least for now.

In fact, I want all the current allowed by the capacitor

According to my calculation, 1.5uF will produce an impedance of 1.7k OHM

220 / 1.7k = 130mA AC

That would burn the 100 OHM resistor, wouldn't it?

I think if there is no resistance, I will burn the Zener tube

So I thought of transistors. If my logic has any basis, just adjust it according to the basis.

I think the bonus will bring more income

Anyone who knows the Zener source of a transistor knows that the AC part does not need a capacitor (it will switch), but I insist on limiting the current this way and let the transistor be responsible for regulating the voltage

I want to solve the vibration problem, I will put the burden

FET

I just need to feed the driver decently

If I understand the data sheet correctly, it seems that UC38xx takes up 17mA at 30V

I think it can be used with 220k resistor

I'm a bit hungry on the 555 here: 25mA to 15V

But it’s been abandoned endlessly, because UC is far from where I can’t reach

The problem is to make 25mA at 12V

I only see 12V Zener regulator that can work 40mA

If there is no better solution to the problem raised, I will use series transistors.

But when I invented, I expected others

I

I’ve said it’s not good before:

that

The red area I want to circle

I know the things in the picture immediately become toast

well 

For my lime

1.5uF produces 1.7k OHM impedance

220 / 1.7k = 130mA

B.C.

I think if there is no resistance, I will burn the Zener tube

The bad thing is that because it is a series circuit, all the current consumed by the power supply cannot be used because part of the current is wasted in the capacitor. The larger the capacitor, the greater the current at the output and the greater the unused current.

As for the Zener diode does not burn, the circuit I made and used is a presence sensor. It has remained open and has existed for more than a year. 

I think

Bonuses bring more income

Those who know the transistor Zener source know

You need a capacitor on the AC part (it will switch), but I insist on limiting the current and let

The transistor is responsible for regulating the voltage

You are right about controlling the tension of the base. The bad thing is that the difference between input and output cannot be large, otherwise there will be no transistors to handle. Linear circuits have their limitations. 

I think to solve the shock problem,

I will burden

It cannot be resolved. 

Only the use of transformers can solve the problem of electric shock, which is why it appears in the most modern equipment. 

I am back with this project

But now I want to start from the most basic

(If it works, I will not appear on this forum)

Like the picture attached to this article, I did it on the prototype board, but:

1- Zener diode gets hot in a few seconds

2- Anode-cathode voltage is different from Zener voltage

Where is the mistake?

1- To avoid confusion, I did not represent the load at the exit. Also because it is variable

2-Colleague KeVTaG’s documents and drawings say that there is a resistor before the Zener diode, but I cannot wear it because it will burn out in addition to reducing the required current.

* 1.5uF is equal to 1700 ohms.

Divide 311V by that and get 170mA, which is what I need

Use 1W Zener diode and 100R resistor in series. 

In order not to interfere with the load, you can turn it on before the resistor. The voltage should be higher than 12V, but since the current is limited, there is no problem. If you want, you can use a lower voltage Zener diode, so the output voltage is 12V. 

Use 470uF/25V capacitors to filter AC power. 

Although the 170mA current is somewhat high for the Zener diode, a better solution is to use a transistor shunt regulator. 

Be your source. Make mistakes, adjust, learn, burn, "shock", etc. It is part of learning and evolution. Rear

Or less...

I bought the sagencom brand once. The circuit is simply an exception. FR4 board, double-sided, radiator, regulator, does not heat under load (d +), works loosely, has protection, and even has 2 (two!) optical couplers + protection. It is almost impossible to obtain this quality at this price. This is a good goal for counterfeiters.

Rear

of course can!

If I were to power sensitive circuits, I would not even use a less protected power supply

My situation is a bit different, because a power supply with a Zener source allows me to reach other voltages, and the plaque can be placed in a half-matchbox...

And... as you know... I study here

(I would rather be shocked than consume the number of components I want to burn)

-----------------

I tried it, Renato, but it was still hot.

I tried to change the resistor, change the Zener diode, change the position of the characters...

Either heating the Zener diode or heating the resistor.

I want to make another application with simple fonts of the same type. This time it is 50mA.

I put a 680nF capacitor in the AC

Only 50mA passes.

On the prototype board, I only put a Zener tube, no resistance, and it works very well. In parallel with the Zener diode, I placed a 22uF capacitor to keep it smooth.

However, two strange things happened: the Zener diode will degrade/damage (voltage loss) when I turn on and off.

I find it strange because 1: I was wrong, or a capacitor in parallel can prevent voltage spikes when opening and closing.

E 2: According to the data sheet, the Zener diode can support 250mA current, the highest peak value can reach 1A!

Another strange thing is that even with the same parts of the prototype board, the printed board does not even work. Zener was damaged immediately and did not heat up.

Observation 1: Zener diode is 1N4728A, 3V3

Obs. 2: I didn't say aloud there to avoid confusion, but I used 1N4007 in series with Zener to increase the voltage from 3V3 to 3V8. But I suspect this is the reason, because after I remove it from the printing plate, the Zener tube will reduce its quality...

Only a capacitor in series with the Zener diode is sufficient

. (Crossed out). It will generate a large current when it is switched on, and it will be even larger if a capacitor is added. It will use his V plus the network's V and try to push all Zener and aff...

Regarding the peak that the ceiling is trying to support: don't expect it. At zero time, electrolytic R can be much higher than network polyester. Who will hold it is the Zener.

Tip 1: If there is only 3v3, please put 1n400x in series. There can be six dozen in the matchbox. As a precaution, +1 to all

Tip2: Assemble, analyze, see how it works, have a brilliant moment, then give up everything and use the suggested font

however,

, Two strange things will happen: Zener will be degraded/damaged (voltage loss) when inserted and unplugged.

Putting a resistor in series with it again will destroy the voltage close to 3.8V.

If it continues to burn, please use a transistor shunt regulator:

In your case, you can eliminate R1 from the circuit. 

R2 can be 1K, and the transistor can be a BD139 or equivalent transistor. 

I saw in the picture a circuit that uses a 3.3uF capacitor.

. (Crossed out). Chain spikes when turned on

make sense.

I did not count on it

good idea

I just want to know the reason for using diodes with cathodes and anodes.

effective

But only 10 ohm resistor

(I think it is enough to reduce the peaking caused by the capacitor.

It is only suitable for low voltage Zener diodes (3V3, 3V6...) because they support large currents.

For Zener diodes like 12V, this is impossible because they can only withstand 70mA of current, and to build this current from 311V, there is only a 15k resistor (it becomes toast).

I took another step and did the step where the Zener adjusts the base of the transistor. At first it can also work, but it can only work with transistors that can handle 400V Vce, such as MJE13001, and I can take it out of the compact lamp.

R2 can be 1K, and the transistor can be a BD139 or equivalent transistor.

In my case, the problem is that if R2 is 1k, the current does not even flow through R2.

All the current flows to the base of the transistor and then to the emitter, burning everything on the way (this is what I experienced-enjoy BE and still 0.6V between BC)

But this is a very promising circuit.

Reasons for a diode with a cathode on the anode

Just to simulate a real Zener diode. There is a negative V above from...

Burn everything on the way (this is what happened to me

High tension... high "tension". This is another reason for this "idiot" to get rid of his head. Oh, please remember...

Positive diode with cathode

? ...Yes. Maybe this little fool in your circuit can prevent some -V from going out of range, which may be the cause of the damage.

it's me again!

Some of the above suggestions are effective, especially those with a capacitor before the rectifier bridge and a simple Zener diode at the output.

But they are not always effective, so I am still looking for a solution

 Elegant and more comprehensive.

I have attached a new suggestion.

Before leaving the burning component, I want to know if anyone sees any flaws in the proposal.

The image is an emulator.

-There are two diodes there to avoid any possibility of current flowing through the gate during the negative cycle. If someone assures me that this is overkill, I will drive them away.

-The emulator can charge 200uA through a 470k resistor, which is very suitable for the gate of the thyristor;

-The charging voltage of the red part is 13.5V, which exceeds the 13V Zener diode by a certain amount to activate the gate;

-The picture is only part of the source. of

Immediately after.

-The purpose of this circuit is to provide no more than 20 volts at the output (green in the image) so that I can use any CI under fine adjustment.

-

After the thyristor, I plan to place capacitors or inductors to keep all components constant (1000uF in the picture, green). I ask those who know SCR whether the DC current in the cathode will turn off the thyristor when the anode crosses zero.

I recommend:

-Don't reinvent the wheel. "Innovative" circuits for simulator operation and analysis by experts

This does not seem to be a very interesting idea. But, of course, there is room for everything. E.g. What I want to say is: your circuit does not work at all, completely inconsistent with the title suggestion, and the actual usage rate is almost zero.

-Search for the network circuit that serves you according to the suggested title

-There is nothing bad for your study. In fact, the opposite is true: we are here to contribute. However, if you don't mind, your circuit cannot be analyzed technically. Ok...at least

Practical point of view.

-Keep working hard, don't go for me

-...

Capacitance source.

You need a capacitor to limit the AC current to 70mA at the lowest possible voltage. Take 100Vac as an example.

When using a 100Vac power supply, a capacitor that limits the current to 70mA.

Then use 4 1N4007 diodes for rectification.

Filter with 1000uF capacitor

Use a Zener diode to limit the voltage to 12V.

You can even use two 1W Zen diodes in parallel to distribute power between them.

It is the most practical resource possible. 

Only 70mA current is consumed at 12V.

At 127Vac or 220Vac, it will not consume 70mA of current, because the reactive current of the capacitor is not counted as power.

Only the current in the resistor or regulator (dissipating 70mA at 12V in this case) is counted as power. 

If you want to make a version by reducing 312V to 12V directly from the linear regulator, the efficiency will be greatly reduced. It will dissipate more power. It easily passes 20 watts of dissipated power.

Using the capacitive power supply version, the power dissipation is even less than 1 watt 

Well, we have shown examples of such sources for six months. 

I just don't understand why friends 

Failed to make it work. 

I even use it to take advantage of the 24VDC contactor on the 120VAC network.

people,

People who use Zener can work (who read my article inadvertently will definitely see it in the first paragraph)

However, in addition to the current limit of the thyristor, the new proposal has no current limit (for this precise model, the current is 800mA, for more robust models, such as the BTA-42 general-purpose dimmer, the current is up to 40A).

Only those who do not understand SCR cannot see the absurd potential of the project: 

You can manufacture a small number of adjustable 40A power supplies. If we start to consider SCR in parallel, it is double or triple... the limit is imagination.

Yes, you can do it. But this is not reliable. 

They only use this circuit for original equipment such as temperature regulators. 

It is not even a good thing for the engine, because it will bring a pulse signal, which will bring noise and be harmful to the engine, thus shortening its service life. 

In electronic circuits, there is no alternative. Because you can't get pure direct current with so few parts, the final sauce is more expensive than pasta. 

However, there are insulation problems. If DC voltage is obtained from the grid, many circuits will become dangerous. 

What you want to do is a controlled rectifier.

But suppose you reduce the capacity from 40A of 220Vac to 12V DC?

You will only have 480 watts available, but 40 amps will be cycled on the network.

It will still be an uninsulated source.

In order to maintain acceptable variations in 12V, huge inductance and capacitance filters will be required. 

This will be more expensive than simply switching sources. 

It will become larger and less efficient. 

It will not be insulated. 

Your ideas are not new. 

I saw the video in a YouTube video, which was stabilized by a thyristor. Thyristor is the predecessor of SCR, it can be used for ionized gas in the tube. A thermal electronic valve.

It is a 120V DC power supply, which is stable. A lot of radio equipment.

Please note that this is the concept of valve time. Old and obsolete things. 

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