13.8V 20A power supply

author: Santa Cruz (Nickname - Bob) - Zagreb, Croatia

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Regulated DC power supply, short circuit safe, and with current limiter

This PSU has been especially designed for current-hungry ham radio transceivers. It delivers safely around 20Amps at 13.8V. For lower currents, a separate current limiting output, capable of 15ma up to a total of 20A has been added. Let us see what we have got here. The power transformer should be capable to deliver at least 25A at 17.5 to 20V. The lower the voltage, the lower power dissipation. The rectified current will be “ironed” by the C1, whose capacity should not be less than 40.000uF, (a golden rule of around 2000uF/A), but we recommend up to 50.000uF. This capacity can be built up by several smaller capacitors in parallel. The base of this design is a simple 12V regulator (7812). The output voltage can be brought to desired value (here 13.8V) by two external resistors (R5 and R6) using this formula:

U= 12(1+R5/R6)

The low currents (here 15mA) will keep the 7812 in its regular function. As soon as the current rises over 15ma, the voltage drop on R4 will “open” the Q3, actually handling the high output current. This is a PNP transistor (Ic>25) and current amplification factor of at least 20. The one that has been tested and proven here is the 2N5683. The current limiting resistance RL, for the maximum output of 20 Amps should be 0.03 Ohms, rated at

least 15W. You can use the resistance wire or switch several resistors in parallel, totaling the resistance/power values. Values for other currents can be calculated by the rule:

RL=0.7/Imax

 The RL and Q2 (3A PNP such as BD330) form a short circuit “automatic fuse”. As soon as the maximum current reaches 20Amps, the voltage drop over the resistor RL will open Q2, and thus limit the B-E Current of Q3. Parallel to Q2 is Q1, which lights the LED 1 whenever the current limiting circuit is active. When the “fuse” is active, the Q2 bridges the R3, so the full current would flow through the IC1, and damage it. Therefore the R4 is inserted, as to limit the IC1 current to 15mA. This makes it possible to run the IC1 without any cooling aid. The LED 2 will light up every time the PSU is switched on.

There is an adjustable current limiter in parallel to the fixed output, thus providing adjustable current source for smaller currents.

This circuit is very simple too. You will notice that there is no current sensing resistor. But it is really there, in a form of the Rds-on resistance of the N-channel FET, which actually handles the load cutoff from the source. The function of the FET is shown in the diagram 2. When the current Id is rising, the tension Uds over the resistance Rds rises very slowly in the beginning, but very fast after the knick. This means, that before the knick the FET behaves as a resistor but after it, works as constant current source.

The D2, R3 and B-E connection of the Q4 will sense the Uds voltage of the FET1. When the voltage rises enough, the Q4 will shortcut the FET1 gate to mass, and cut the current flow through the FET 1 off. However, to enable the FET1 to open, there is certain gate voltage necessary, which in this case is brought up by the voltage divider consisting of R8, Z1, P1 and R9. So the maximum Gate voltage will be the one of the Z1, and the minimal will be around 3V6. The Z1 voltage (Uz1) will thus determine the max current flowing through the FET 1.

The diagram 2 will show that for 5 Amps the Uz1 should be 5V6, and for 20Amps around 9V6. The Capacitor C4 will determine the “velocity” or the reaction time of the limiter. 100 uF will make the reaction time to be around 100ms, and 1n will make it 1us.

Within the designed limits, the P1 will limit the current output in the range of 15mA to 20A. You can use both output simultaneously, but the total output current will be limited by the value of the RL. This PSU can be built also for higher outputs, as long as the transformer will handle the current requirements, and you provide sufficient cooling for the Q3.

If somebody will be interested, there is a PCB design ready.

Have fun.

Bob

REV1.

I have received several requests for some modifications, and the one I find useful is the addition of an amp meter. Therefore the slightly modified diagram is included in this revision. All elements within the dotted border are now placed on the pcb. There is also elements placement design included. Should one have an 25Amp instrument on hand, there is nothing easier. Just mount it in line and there it goes. However, a ham would probably find an instrument somewhere in his “junk-box”, but the scale would be something completely different, let say an “S” or Voltmeter. No problem. We already have a “shunt” for the amp-meter, and it is there as the Current limiting resistor “RL”. As already known from before, there is a voltage drop of 0V7 over the resistor at current flow of 20A. What we now have to do, is to simply measure the voltage drop over the resistor, and co-relate it with the current. Let us say that our instrument has an internal resistance of 13R, and has a full scale reading of 60mV. The voltage drop over the RL is 0V7 for 20Amps. Therefore, we need another resistance in line with the instrument, that would bring the 0V7 to 60mV, or an voltage drop of 640mV.

The formula is simple:

U1:R1=U2:R2

60:13=640:X

X=13x640/60

X=138.66

Therefore, the resistance that has to be inserted in line is around 140R. I suggest to insert a trimmer (VR1) of around 200R, to fine trim the reading when calibrating the instrument. Using your favorite drawing software, design your scale to your likings, (at least 20A for the full scale) and insert it in the instrument you have. Due to the many requests for the PCB Layout, I have included the design here. The exact dimensions of the pcb are 160x100mm. Please remember, that the pcb has to be printed as a mirror image, to obtain higher quality when transferring it to the copper side of the board.

Wish you a good time.

Bob

LT3650-4.1 7.5V to 32V Single-Cell Li-Ion 2A Charger

The LT3650 is a complete monolithic single-cell Li-Ion/ Polymer battery charger that operates over a 4.75V to 32V input voltage range (7.5V minimum start-up voltage). The LT3650 provides a constant-current/constant-voltage charge characteristic, with maximum charge current externally programmable up to 2A, set using an external current sense resistor. A precondition feature trickle charges a low voltage battery, and bad-battery detection provides a signal and suspends charging if a battery does not respond to preconditioning.

The LT3650 can be configured to terminate charging when charge current falls to C/10, or one-tenth the programmed maximum current. Once charging is terminated, the LT3650 enters a low current (85μA) standby mode. An auto-restart feature starts a new charging cycle if the battery voltage drops 2.5% from the fl oat voltage, or if a new battery is inserted into a charging system.

The LT3650 contains a user-programmable internal safety timer (typically set to a three hour full cycle time). The IC can be configured to use this internal timer if a time-based termination scheme is desired in which charging can continue below C/10 until a desired time is reached.

The LT3650 is available in a low profile (0.75mm) 3mm × 3mm 12-pin DFN and 12-pin MSOP packages.

Charger with protection.

At work, the equipment was written off and I got a power unit without guts, with an inscription on the front panel "statron TYP 2230". In the presence of the body and installed inside the power transformer. According to the inscription on the output terminals (13.8V / 10A), the transformer was quite powerful and the output voltage of the power winding at idle was about 16 volts. I decided to leave it for the time being.
Cold came and the relative asked me to collect for his fleet of cars a charger for car batteries, reliable and to normally charge the battery and did not fail for accidental shorts of output terminals and incorrect connection of batteries. The pair of impulse chargers "Orion PW415" purchased by him earlier did not work for a month in street operating conditions (one and a week), and burned well inside from dust and water drops that got there and subsequently occurred a breakdown, which had not yet been recovered. I remembered about the power supply left to the best of times, or rather everything that was left of it, it was ideally suited for the realization of the task, and there was plenty of space in the case.

После просмотра различных вариантов схем, в качестве основы была выбрана схема промышленного зарядного устройства "Барс-8А". Нового здесь ничего не открою, эта схема есть на просторах "инета", просто она удовлетворяла всем запросам заказчика.
Трансформатор, установленный в имеющемся блоке питания, имел одну силовую обмотку на 16 вольт ХХ и в принципе вполне подходил для зарядного, исходная схема которого имела трансформатор с вторичной обмоткой со средней точкой. Исходя из имеющегося трансформатора, исходная схема была немного переделана, а конкретнее были добавлены два диода VD7 и VD8 для обеспечения мостовой схемы выпрямителя от одной обмотки.

In principle, it is perfectly possible to use any suitable power transformers with one winding and with a winding with an average point, with voltage at XX within 16-22 volts - only the rectifying part of the charger will change. 
For example, if you use a transformer with a secondary winding with an intermediate point as a power transformer, the rectifier diodes can be removed, and the power part diagram will look like this.

Generally, the power of this circuit is limited by the power transformer and rectifying diodes and thyristors used in it. 
The circuit itself does not work if the battery is not connected to the output, or is connected in the wrong polarity. Just at the output in this case, nothing will happen, at least short the output terminals. 
An ammeter (milliammeter with a shunt) was inserted into the existing power supply, a regulator of the charging current (voltage) was installed, one more LED (green) for indicating the device's inclusion in the network. The existing LED (red) was used to indicate the correct polarity of the battery connection.

The circuit was assembled on the board by mounted mounting, diodes and thyristors were installed on a common radiator through insulating gaskets. As diodes and thyristors, we chose thyristors KU202 and 10 ampere diodes. Of course, it's better to put them more powerful, but based on the available trance with a voltage of about 20 V, let's hope that the maximum charging current of the device does not exceed 10-12 amperes, which is enough for them. For better cooling, a fan was installed in front of the radiator from the computer power supply unit.

The shunt for the ammeter was made of knitting iron wire, 2 mm in diameter. Its length is selected by an experimental method, according to the maximum deviation of the milliammeter needle at a current of 10 amperes. Low-power transistors here can apply any, appropriate structure, as KT815G - any medium (large) power. 
The device can be assembled on a printed circuit board, 50x65 mm in size. See below for the board variant.

I want to note that this charger is assembled from serviceable parts and without errors in the installation - it does not need to be adjusted and starts working immediately. The device is reliable in operation and will not accidentally disable it. For even more reliable operation, as power elements, it is better to use thyristors (diodes) for a current of at least 25 amperes. 
I hope this device does not disappoint you. 
Good luck in the assembly! 

Comparators, how they work.

General information.

The comparator is an operational amplifier without feedback with a large gain. 
Therefore, if you apply a certain constant level of the reference voltage to one input (for example, inverted), and a variable signal to the other input (direct), the output voltage will change abruptly from minimum to maximum at the moment when the level of the input signal exceeds the level the reference voltage signal set at the other input, and vice versa.

Comparators have two inputs, direct and inverse, and depending on the desired result, the reference and compared voltages can be connected to any input. 
If the input voltage on the direct input exceeds the voltage of the inverse input, the output transistor of the comparator opens, if it becomes lower, it closes. That is, the comparator compares the voltages. 
So we came to the essence of the main purpose of the comparator - to compare the two voltages (signal) and to output the voltage (signal) at the output in the event that the signal at one input became more or less than the level set by the reference voltage of the other input.
Comparators can be used to assemble various devices, such as thermostats, stabilizers, various automation devices-using different sensors such as thermistors, photoresistors, moisture indicators, etc. to change the input signal. etc. 
The output stages of the comparators are designed in such a way that their output voltage corresponds to the input logic level of many digital microcircuits, so they can still be called shapers. 
In principle, on any operational amplifier, it is possible to build a comparator (but not vice versa). 
Consider the most common comparator K554CA3, (foreign analogs LM-111, LM-211, LM-311).
The output of this comparator includes a transistor with an open collector and an emitter, and depending on the desired output, it can be connected in a common emitter or emitter follower scheme. 
The scheme of switching on the comparator for a single-polar power supply is shown in Figure 1, for the two-polar power supply in Figure 2.

Figure 1.
Diagram of switching the comparator into a single-polar power supply. 
a - with a common emitter; b - emitter follower. 
The supply voltage +5 volts is indicated for the logic level of TTL microcircuits.

To match the output to the logic levels of the CMOS chips, the supply voltage can be respectively 9-15 volts.

Figure 2.
Diagram of switching the comparator in two-polar power. 
a - with a common emitter; b - emitter follower.

As a load of the comparator, you can use any load with a current consumption of not more than 50 mA. This can be directly the relay windings, resistors, indication LEDs and optocouplers of actuators, with current limiting resistors. Inductive loads should preferably be shunted by diodes from reverse voltage ejection. 
The supply voltage of the comparator can be 5 - 36 volts single-polar (or sum of two-polar) voltage.

Processes for switching comparators.

If the input signal changes very slowly, when the input signal reaches the reference level, the output of the comparator can repeatedly change its state with a high frequency under the influence of minor interference (so-called "bounce"). 
To eliminate this phenomenon, a positive feedback (PIC) is introduced into the comparator circuit, which provides the comparator characteristic with a small hysteresis, that is, a small difference between the input voltages of switching on and switching off the comparator. Some types of comparators already have a built-in, the above-mentioned PIC. 
It can also be entered into the comparator circuit, if necessary, for example, as shown in the figure below.

Figure 3.
The scheme of inclusion in the PIC comparator (hysteresis).

Figure 3 shows the circuit of the inclusion of a comparator with an open collector at the output, the transient response of which has a hysteresis (Fig. 3b). 
The threshold voltages for this circuit are determined by the formulas;

Although the hysteresis makes a small delay in switching the comparator, but thanks to it, the "output" voltage is completely reduced or even completely eliminated. 

For someone who wants a more complete and detailed acquaintance with comparators, I recommend reading B. Uspensky's article in the HSRL No. 97 p. 49.

We connect an unknown transformer to the network.

Nikolay Petrushov

How to deal with the windings of the transformer, how to properly connect it to the network and not "burn" and how to determine the maximum currents of secondary windings ??? 
Such and similar questions are asked to themselves by many novice radio amateurs. 
In this article, I will try to answer similar questions and on the example of several transformers (photo at the beginning of the article), deal with each of them .. I hope this article will be useful to many radio amateurs.

To begin with, remember the common features for armored transformers 

- The mains winding, as a rule, is wound first (closest to the core) and has the greatest active resistance (unless it is a step-up transformer or a transformer having anode windings).

- The mains winding can have bends, or consist for example of two parts with outlets.

- The serial connection of the windings (parts of the windings) in armored transformers is made as usual, beginning with the end or terminals 2 and 3 (if for example there are two windings with terminals 1-2 and 3-4).

- Parallel connection of windings (only for windings with the same number of turns), as usual start with the beginning of one winding, and end with the end of the other winding (n and k, or pins 1-3 and 2-4 - if for example there are identical windings with terminals 1-2 and 3-4).

General rules for connecting secondary windings for all types of transformers.

To obtain different output voltages and load currents for individual needs other than those available on the transformer, it is possible to obtain by various connections of the existing windings among themselves. Let's consider all possible variants. 

- The windings can be connected in series, including windings wound around a different diameter wire, then the output voltage of such winding will be equal to the sum of the voltages of the connected windings (U = U1 + U2 ... + Un). The load current of such a winding will be equal to the lowest load current from the existing windings. 
For example: there are two windings with voltages of 6 and 12 volts and 4 and 2 ampere load currents. As a result, we get a common winding with a voltage of 18 volts and a load current of 2 amperes. 

- Windings can be connected in parallel,Only if they contain the same number of turns , including wound by a different diameter wire. The correctness of the connection is checked as follows. We connect the two wires together from the windings and measure the voltage on the remaining two wires. 
If the voltage is doubled, the connection is not correct, in this case, change the ends of any of the windings. 
If the voltage at the remaining ends is zero, or so (a difference of more than half a volt is not desirable, the windings in this case will bask on the XX), boldly connect the remaining ends together. 
The total voltage of such a winding does not change, and the load current will be equal to the sum of the load currents, of all windings connected in parallel. 
(I = I1 + I2 ... + In) .
For example: there are three windings with an output voltage of 24 volts and load currents of 1 ampere. As a result, we get a winding with a voltage of 24 volts and a load current of 3 amperes. 

- The windings can be connected in parallel-series (for the parallel connection, see the point above). The total voltage and current will be the same as in a series connection. 
For example: we have two in series and three parallel-connected windings (the examples described above). We connect these two composite windings in series. As a result, we get a common winding with a voltage of 42 volts (18 + 24) and a load current at the smallest winding, that is - 2 amperes.

- The windings can be connected in the opposite direction, including windings wound in different diameters (also parallel and series-connected windings). The total voltage of such a winding will be equal to the difference in voltages included in the opposite direction of the windings, the total current will be equal to the least current in the winding load. This connection is used when it is necessary to lower the output voltage of the existing winding. In the same way, to lower the output voltage of any winding, it is possible to overcoat all windings with an additional winding with a wire, preferably not less than the diameter of the winding whose voltage must be lowered, so that the load current does not decrease. The winding can be wound up without even examining the transformer, if there is a gap between the windings and the core , and turn it on against the required winding.
For example: we have two windings on the transformer, one 24 volt 3 amps, the second 18 volts 2 amps. We turn them on and we will end up with a winding with an output voltage of 6 volts (24-18) and a load current of 2 amperes. 
But this is purely theoretical, in practice, the efficiency of such an inclusion will be lower than if the transformer had one secondary winding. 
The point is that the current flowing through the windings creates in the EMF windings, and in a larger winding the voltage decreases with respect to the voltage XX, and in th e nshey - increases, and the greater the current flowing through the coils - the greater this effect. 
As a result, the total rated voltage (at rated current) will be lower.

Let's start with a small transformer, adhering to the above features (left in the photo). 
We examine it carefully. All his conclusions are numbered and the wires approach the following conclusions; 1, 2, 4, 6, 8, 9, 10, 12, 13, 22, 23, and 27. 
Next, you need to call the ohmmeter with all the terminals to determine the number of windings and draw a transformer diagram. 
The following picture is obtained. 
Conclusions 1 and 2 - the resistance between them is 2.3 Ohms, 2 and 4 - 2.4 Ohm between them, between 1 and 4 - 4.7 Ohm (one winding with an average terminal). 
Next 8 and 10 - resistance of 100.5 Ohm (one more winding). The conclusions of 12 and 13 are 26 Ohms (another winding). Conclusions 22 and 23 - 1.5 Ohm (the last winding).
Conclusions 6, 9 and 27 do not ring the other conclusions and among themselves - it's most likely the screen windings between the mains and other windings. These terminals are connected to each other in the finished structure and connected to the housing (common wire). 
Once again, carefully inspect the transformer. 
The network winding, as we know, shakes first, although there are exceptions.

It's hard to see in the photo, so I'll duplicate it. The lead from the core itself is soldered to terminal 8 (that is, it is closest to the core), then there is a wire to pin 10 - that is, the winding 8-10 is wound first (and has the highest active resistance) and is likely to be network. 
Now, from the received data from the dial, it is possible to draw a diagram of the transformer.

It remains to try to connect the supposed primary winding of the transformer to the network of 220 volts and check the no-load current of the transformer. 
To do this, we compile the following chain.

Consistently with the proposed primary winding of the transformer (we have 8-10 conclusions), we connect a conventional incandescent lamp with a power of 40-65 watts (for more powerful transformers 75-100 watts). The lamp in this case will play the role of a kind of fuse (current limiter) and protect the transformer winding from its failure when connected to the 220 volt network, if we chose the wrong winding or the winding is not rated for 220 volts. The maximum current flowing in this case along the winding (at a lamp power of 40 watts) will not exceed 180 milliamps. This will save you and the transformer under test from possible troubles.

-And in general, take yourself for a rule, if you are not sure of the correct choice of the network winding, its switching, in the installed jumpers of the winding, then the first connection to the network should always be made with a sequentially switched incandescent lamp.

By taking care, we connect the assembled circuit to the 220 volt network (I have a slightly higher voltage, or more precisely 230 volts). 
What do we see? The incandescent lamp does not light. 
This means that the network winding is selected correctly and further connection of the transformer can be made without a lamp. 
We connect a transformer without a lamp and measure the no-load current of the transformer.

The idle current (XX) of the transformer is measured as follows; a similar circuit is assembled that we collected with a lamp (I will not draw any more), but instead of the lamp, an ammeter is switched on, which is intended for AC measurement (carefully inspect your device for this mode). The ammeter is first set to the maximum measurement limit, then, if it is large, the ammeter can be switched to a lower measuring limit. Being careful - we connect 220 volts to the mains, preferably through a separating transformer. If the transformer is powerful, then the probes of the ammeter must be short-circuited either by an additional switch or simply short-circuited with each other, since the starting current of the primary winding of the transformer exceeds the no-load current by 100-150 and the ammeter can fail. After,

The idle current of the transformer should ideally be 3-8% of the rated current of the transformer. It is also considered normal and current is 5-10% of the nominal. That is, if the transformer with a rated power of 100 watts, the current consumption of its primary winding will be 0.45 A, then the current XX should ideally be 22.5 mA (5% of the nominal value) and preferably not exceed 45 mA (10 % of the nominal).

As you can see, the no-load current is slightly more than 28 milliamperes, which is quite acceptable (well, it may be slightly overestimated), because this type of transformer is 40-50 watts in appearance. 
We measure the no-load voltage of the secondary windings. It turns out at conclusions 1-2-4 17.4 + 17.4 volts, the conclusions 12-13 = 27.4 volts, the conclusions 22-23 = 6.8 volts (this is at a voltage of 230 volts). 
Next, we need to determine the capabilities of the windings and their load currents. How it's done? 
If it is possible and allows the length of wires suitable for contacts, it is better to measure the diameters of the wires (roughly 0.1 mm - with a caliper and exactly a micrometer), and in the table HERE , with an average current density of 3-4 A / mm.kv. - we find currents that are capable of producing windings.
If it is not possible to measure the diameters of the wires, we proceed as follows. 
We load each of the windings in turn with an active load, which can be anything, for example, incandescent lamps of different power and voltage (incandescent lamp with a power of 40 watts for 220 volts has an active resistance of 90-100 ohms in a cold state, a lamp with a power of 150 watts - 30 Ohm), wire resistors (resistors), nichrome spirals from electric tiles, rheostats, etc. 
We load until the voltage on the winding is reduced by 10% relative to the idling voltage. 
Then we measure the load current.

This current will be the maximum current that the winding will be able to produce for a long time without overheating.

Conditionally accepted value of voltage drop to 10% for constant (static) load in order not to overheat the transformer. You can easily take 15%, or even 20%, depending on the nature of the load. All these calculations are approximate. If the load is constant (glow of lamps, for example, the charger), then a smaller value is taken if the load is impulse (dynamic), for example, ULF (except for mode "A"), then we can take the value and more, up to 15-20%.

I take into account the static load, and I did it; winding 1-2-4 load current (when the winding voltage decreases by 10% relative to the idling voltage) - 0.85 amperes (power about 27 watts), winding 12-13 (pictured above) load current 0.19-0, 2 amperes (5 watts) and winding 22-23 - 0.5 amperes (3.25 watts). The rated power of the transformer is about 36 watts (rounded to 40). 

Yes, I also want to talk about the resistance of the primary winding. 
For low-power transformers, it can be dozens, or even hundreds of ohms, and for high-power transformers it can be one ohm. 
Very often the forum asks such questions; 
"I measured the resistance of the primary winding TS250 with a multimeter, but it turned out to be 5 ohms.Is it too little for a 220 volt network, I'm afraid to include it in the network.

Since all multimeters measure DC resistance (resistance), you should not worry, because for an alternating current of 50 Hz, this winding will have a completely different resistance (inductive), which will depend on the inductance of the winding and the frequency of the alternating current. 
If you have, than measure the inductance, then you yourself can calculate the resistance of the winding to alternating current (inductive resistance). 

For example; 
The inductance of the primary winding during the measurement was 6 GH, we go hereand enter these data (inductance 6 H, frequency of the current network 50 Hz), look - it turned out 1884.959 (round 1885), this will be the inductive resistance of this winding for a frequency of 50 Hz. From here you can calculate the idle current of this winding for 220 volts - 220/1885 = 0.116 A (116 milliampere), yes, you can add 5 ohms resistance, that is, it will be 1890. 
Naturally, for a frequency of 400 Hz there will be quite a different resistance of this winding.

Similarly, other transformers are checked. 
The photo of the second transformer shows that the leads are soldered to the contact lobes 1, 3, 4, 6, 7, 8, 10, 11, 12. 
After the dullness, it becomes clear that the transformer has 4 windings. 
The first one at terminals 1 and 6 (24 Ohm), the second 3-4 (83 Ohms), the third 7-8 (11.5 Ohms), the fourth 10-11-12 with the branch from the middle (0.1 + 0.1 Ohms) .

And it is clearly seen that the winding 1 and 6 is wound first (white terminals), then there is a winding 3-4 (black terminals). 
24 Ohm active resistance of the primary winding is enough. For more powerful transformers, the active resistance of the winding reaches to units of Ohm. 
The second winding 3-4 (83 Ohms), possibly boosting. 
Here you can measure the diameters of the wires of all windings, except windings 3-4, the terminals of which are made of black, multi-strand, mounting wire.

Further we connect the transformer through the incandescent lamp. The lamp does not light, the transformer looks 100-120 in capacity, we measure the no-load current, it turns out 53 milliamperes, which is quite acceptable. 
We measure the idling voltage of the windings. It turns out 3-4 - 233 volts, 7-8 - 79.5 volts, and the winding 10-11-12 at 3.4 volts (6.8 with an average output). We load the winding 3-4 before the voltage drop by 10% of the idling voltage, and measure the flowing current through the load.

The maximum load current of this winding, as can be seen from the photograph, is 0.24 amperes. 
The currents of other windings are determined from the current density table, based on the diameter of the winding wire. 
Winding 7-8 is wound by a wire 0,4 and a filamentary wire 1,08-1,1. Accordingly, the currents are 0.4-0.5 and 3.5-4.0 amperes. The nominal power of the transformer is about 100 watts.

There was one more transformer left. He has a contact strip with 14 contacts, top 1, 3, 5, 7, 9, 11, 13 and bottom are respectively even. It could switch to various network voltages (127,220,237) It is quite possible that the primary winding has several branches, or consists of two semi-windings with taps. 
We are calling, and this is the picture: 
Conclusions 1-2 = 2.5 Ohm; 2-3 = 15.5 Ohm (this is one winding with a tap); 4-5 = 16.4 Ohm; 5-6 = 2.7 Ohms (another winding with tap); 7-8 = 1.4 Ohm (3rd winding); 9-10 = 1.5 Ohm (4th winding), 11-12 = 5 Ohm (5th winding) and 13-14 (6th winding). 
We connect to terminals 1 and 3 a network with a series-connected incandescent lamp.

The lamp burns in half the heat. We measure the voltage at the terminals of the transformer, it is equal to 131 volts. 
It means that the primary winding here consists of two parts, and the connected part at 131 volts voltage starts to go into saturation (the no-load current rises) and the lamp thread is then heated up. 
We connect jumper terminals 3 and 4, that is, consistently two windings and connect the network (with a lamp) to terminals 1 and 6. 
Hurray, the lamp does not burn. We measure the no-load current.

The no-load current is 34.5 milliamps. Here, most likely (since part of winding 2-3 and part of the second winding 4-5 have more resistance, these parts are designed for 110 volts, and parts of windings 1-2 and 5-6 for 17 volts, that is common for one part of 1278 volts), 220 volts was connected to terminals 2 and 5 with a jumper on terminals 3 and 4 or vice versa. But you can leave and the way we connected, that is, all the parts of the windings consistently. For a transformer, this is only better. 
Everything, the network is found, the further actions are similar to those described above.

A little more about the rod transformers. For example, there is such a (photo above). What are the common features for them?

- In rod transformers, as a rule, two symmetrical coils, and the network winding is divided into two coils, that is, one coil wound coils of 110 (127) volts, and the other. The numbering of the outputs of one coil is the same as the other, the numbers on the other coil are marked (or conditionally marked) with a stroke, i.e. 1 ', 2', and so on.

- The mains winding, as a rule, is wound first (closest to the core).

- The mains winding can have bends, or consist of two parts (for example one winding - pins 1-2-3, or two parts - pins 1-2 and 3-4).

In the core transformer, the magnetic flux moves along the core (along the "circle, ellipse"), and the direction of the magnetic flux of one rod will be opposite to the other, so to connect the two halves of the windings in series, on different coils connect the same-name contacts or the beginning with the beginning (end with end ), i.e. 1 and 1 ', the network is fed to 2-2', or 2 and 2 ', the network is then fed to 1 and 1'.

- For the series connection of windings consisting of two parts on one coil, the windings are connected as usual, the beginning with the end or the end with the beginning, (nc or k-n), that is, terminals 2 and 3 (if, for example, there are 2 windings with pin numbers 1-2 and 3-4), as well as on the other coil. Further serial connection of the resulting two semi-windings on different coils, see the point above. (An example of such a connection on the transformer circuit is TC-40-1 ). 

- For parallel connection of windings ( only for windings with the same number of turns) on one coil, the connection is made as usual (n and k, or leads 1-3 and 2-4 - if for example there are identical windings with leads 1-2 and 3-4). For different coils, the connection is made as follows, k-n-tap and n-k-tap, or connect leads 1-2 'and 2-1' - if for example there are identical windings with leads 1-2 and 1'-2 ' .
 

I remind you once again of the safety precautions, and it is best for experiments with a voltage of 220 volts to have a separating transformer at home (a transformer with 220/220 volt coils for galvanic isolation with an industrial network), which will protect against electric shock, by accidentally touching the bare end of the wire .

If you have any questions about the article, or find a transformer in the zagashniki (with suspicion that he is a power), ask questions HERE , we'll help you figure out with his windings and connection to the network.

TL431, what kind of "beast" is this?

Fig. 1 TL431.

TL431 was created in the late 70's and is currently widely used in industry and in amateur radio activity. 
But despite her solid age, not all radio amateurs are intimately familiar with this wonderful body and its capabilities. 
In the proposed article I will try to acquaint the radio amateurs with this chip. 

First, let's see what's inside it and turn to the documentation for the microcircuit, the "datasheet" (by the way, the analogs of this chip are KA431, and our chips KR142EN19A, K1156ER5x). 
And inside it has a dozen transistors and only three conclusions, so what is it?

Fig. 2 Device TL431.

It turns out all very simple. Inside is a conventional op-amp operational amplifier (a triangle in a block diagram) with an output transistor and a reference voltage source. 
Only here this circuit plays a slightly different role, namely, the role of the zener diode. It is also called the "Controlled Zener diode". 
How does he work? 
See the block diagram of TL431 in Figure 2. It is seen from the diagram that the op-amp has a (very stable) built-in 2.5v reference voltage source (small square) connected to the inverse input, one direct input (R), a transistor at the OU output, a collector K) and emitter (A), which are combined with the power outputs of the amplifier and a protective diode from the reverse polarity. The maximum load current of this transistor is up to 100 mA, the maximum voltage is up to 36 volts.

Fig. 3 The pinout is TL431.

Now, using the example of a simple diagram depicted in Figure 4, we will analyze how this works. 
We already know that inside the chip there is a built-in reference voltage source - 2.5 volts. The first releases of microcircuits, which were called TL430 - the voltage of the built-in source was 3 volts, in later releases, it reaches 1.5 volts. 
Therefore, in order to open the output transistor, it is necessary to input the input amplifier (R), supply voltage - slightly exceeding the reference 2.5 volts, (the prefix "a little" can be omitted, since the difference is several millivolts and in the future we will assume that on the input you need to apply a voltage equal to the reference one), then the output of the operational amplifier will appear voltage and the output transistor will open.
To put it simply, the TL431 is something like a field effect transistor (or simply a transistor), which opens at a voltage of 2.5 volts (or more) applied to its input. The threshold for opening and closing the output transistor here is very stable due to the presence of a built-in stable reference voltage source.

Fig. 4 Scheme on the TL431.

From the circuit (Figure 4), it is seen that the input R of the TL431 chip, the voltage divider from the resistors R2 and R3 is switched on, the resistor R1 limits the LED current. 
Since the resistors of the divider are the same (the voltage of the power supply is divided in half), the output transistor of the amplifier (TL-ki) will open at a voltage of 5 volts or more (5/2 = 2.5). At the input R in this case, 2.5 volts will be fed from the divider R2-R3. 
That is, the LED at us will light up (the output transistor will open) at a voltage of a power source - 5 volts and more. It will die out accordingly when the voltage of the source is less than 5 volts.
If you increase the resistance of the resistor R3 in the divider's arm, it will be necessary to increase the voltage of the power supply by more than 5 volts, so that the voltage at the input R of the microcircuit from the divider R2-R3 again reaches 2.5 volts and the output transistor TL opens -yes. 

It turns out that if this voltage divider (R2-R3) is connected to the output of the PSU and the cathode of the TLK to the base or gate of the regulating transistor BP, then changing the divider arms, for example by changing the value of R3 - it will be possible to change the output voltage of this PSU, because at the same time, the stabilization voltage of the TL-ki (the opening voltage of the output transistor) will change - that is, we get a controlled zener diode.
Or if you choose a divider without changing it in the future - you can make the output voltage of the PSU strictly fixed for a certain value. 

Conclusion; - If the microcircuit is used as a zener diode (its main purpose), then we can make a zener diode with any stabilization voltage within 2.5-36 volts (the maximum limitation in "datasheet") by choosing the resistor of the R2-R3 divider. 
The voltage of stabilization in 2.5 volts is obtained without a divider if the TL input is connected to its cathode, that is, to close conclusions 1 and 3.

Then there are still questions. can I for example replace the TL431 with a regular opamp?
- It is possible only if there is a desire to design, but it will be necessary to assemble its reference voltage source by 2.5 volts and supply power to the opamp separately from the output transistor, since the current of its consumption can open the actuator. In this case, you can make the reference voltage anything (not necessarily 2.5 volts), then you will need to recalculate the divider resistors used in conjunction with the TL431, so that at a given output voltage of the PSU, the voltage applied to the input of the chip is equal to the reference voltage. 

One more question - is it possible to use TL431 as a normal comparator and assemble on it, say, a thermoregulator, or something like that?

- It is possible, but since it differs from the usual comparator already by the presence of a built-in reference voltage source, the circuit will be much simpler. For example, such;

Fig. 5 Thermostat on the TL431.

Here the thermistor (thermistor) is a temperature sensor, and it reduces its resistance when the temperature rises, i.e. has a negative TCR (Temperature Coefficient of Resistance). Thermoresistors with positive TCR, i.e. the resistance of which increases with increasing temperature - called posistors. 
In this thermoregulator, when the temperature exceeds the set temperature (regulated by a variable resistor), the relay or some kind of actuator will operate, and disconnect the load (s) from the contacts, or for example turn on the fans depending on the task.
This circuit has a small hysteresis, and to increase it, it is necessary to introduce an OOS between terminals 1-3, for example a tuning resistor of 1.0-0.5 mΩ and its value to be determined experimentally, depending on the necessary hysteresis. 
If it is necessary for the actuator to operate when the temperature is lowered, then the sensor and regulators need to be reversed, that is, insert the thermistor into the upper arm and the alternating resistance with the resistor into the lower arm. 
And finally, you can easily figure out how the TL431 chip works in the power supply circuit for the transceiver, which is shown in Figure 6, and what role the R8 and R9 resistors play, and how they are selected.

Fig. 6 Powerful power supply for 13 volts, 22 amps

Repair of memory of screwdriver Bosch AL 1115 CV (10.8 Li) - 2 attempt

Repair of memory of screwdriver Bosch AL 1115 CV (10.8 Li) - 2 attempt

Charger Bosch AL 1115 CV (10.8 Li), which I already repaired , came back. Without signs of life. Interestingly, without traces of magic smoke, on which, as is known, all electronics work.

We proceed to repair. I changed the legless power transistor STD7NM60M to STP5NK80Z in TO-220, because the first was soldered on the snot, and another 800V permissible on the drain of the second - the pledge of my sound sleep - bought a noodle at a discount of two dozen. Here he was soldered to the same copper (photo from the past). 

Does not start. Sobbing and going out. During the investigation I changed / checked everything.

Resistors, diodes, electrolytes in the secondary, optocoupler, 1N4148, snubber, even TL431. The LED flashes hysterically, at the sink of the needle two hundred volts. Something does not break out, there is not enough of a push. Already thought about implanting UC3843, to resolve the burden in one fell swoop.

Took part in the experiments. In place of V6 soldered different shit : 2SC945, 1815, BC850c - with the last device suddenly wound up and when I again soldered FMMT624 - continued to work, as if nothing had happened. But still BC850c is sick, I did not pull the devil by the beard.

In the meantime, C4 increased to nominal 3nF (MKP), changed capacity in the secondary to "better" in the search process.

Working. Half a day and a dozen strong cigarettes.

UPD increased the capacity of 22u * 450v, put the bank 68u * 400v 105 deg., ESR 0.66 ohm - for the mode of operation of the autogenerator from the voltage varies markedly. Will help to survive in a bad network.