Can a master do construction without such an indispensable tool as a screwdriver? It will not be possible to carry out full-fledged work without using such a tool, because you always need to tighten or strengthen something somewhere. This need for a screwdriver in the household is explained by its functionality and ability to significantly facilitate some of the stages of construction and finishing work.
You may not know which screwdriver is better, but you will definitely appreciate all its capabilities, especially those who have previously screwed in screws with a screwdriver. But, like any equipment, a cordless screwdriver loses its former efficiency over time and no longer works with as much power as before. How to solve such a problem if it occurs? Of course, you can purchase another battery, but the cost of a new battery is steep, so the craftsmen offer an alternative - making a 12V power supply for the screwdriver with your own hands. This is an excellent way out of the situation and a great opportunity to try your hand at radio engineering.
Stages of preliminary work: preparing for construction
Before you start remaking the battery, select another power supply unit that is suitable in size, then it must be placed in the existing case and secured. Everything is removed from the inside of the prepared device and the internal space is measured, which differs from the external contents.
What you need to know before starting construction
Study the markings or design features indicated on the body of the working tool, and, based on these indicators, determine the voltage required for power supply. In our case, it will be enough to assemble a 12V power supply for a screwdriver with your own hands. If the required ratings are other than 12V, continue to look for an interchangeable option. Having chosen an analogue, calculate the current consumption of the screwdriver, since the manufacturer does not indicate this parameter. To find out, you will need to know the power of the device.
If you don’t have time to select a device, and the calculations take too much time, take any power supply you come across. When buying it, in addition to the current, ask about the battery capacity. To construct a 12V power supply for a screwdriver with your own hands, a device with a capacity of 1.2A and a charge of 2.5 will be sufficient. Remember, before looking for recharging, determine the following necessary parameters:
- Block dimensions.
- Minimum current.
- Required voltage level.
The process of designing a battery pack for a screwdriver
Having selected a new device and all the parts necessary for design, you can begin to work. Assembling a 12V power supply for a screwdriver with your own hands consists of the following steps:
- Having selected the optimal power supply, check it for similarity with the declared characteristics, which will depend on which screwdriver. It is better to use a computer block as the basis for a new battery.
- Disassemble the screwdriver and remove the old drive. If the body is glued, gently tap along the seam with a hammer or score using a thin knife blade. This way you will open the box with the least damage.
- Unsolder the cord and leads from the plug and separate them from the rest of the structure.
- In the place where the battery power supply for the screwdriver was previously located, place the other contents removed from the case.
- Lead the power cord through the opening in the housing. Connect it to the power supply by soldering it in place.
- Use soldering to connect the output of the computer power supply to the battery terminals. Remember to maintain polarity.
- Connect the designed battery to the device and test it.
- If the dimensions of the new charger exceed those of the old battery, it can be built inside the screwdriver handle.
- To limit the supply of voltage from the network to the battery with a parallel supply output, install a diode with the required power from inside the “+” cable break between the battery socket, including the output, but with the “-” pole towards the engine.
What does this battery upgrade give?
Transforming the power supply for a computer into a battery for a screwdriver operating continuously from the mains has a number of advantages, namely:
- There is no need to worry about periodically recharging the device.
- Downtime during long periods of operation is reduced to a minimum.
- The torque remains constant thanks to the constant current supply.
- Connecting a converted computer power supply for a screwdriver (12V) does not in any way affect the technical parameters of the product, even if the device has not been used for a long period of time.
The only quality that is mentioned as a disadvantage is the presence of an electrical outlet near the work site. This problem can be easily solved by connecting an extension cord.
Materials and working tools for upgrading a screwdriver
Remaking a computer power supply for a screwdriver is not difficult; moreover, such an activity is educational, especially for beginners in the field of radio mechanics. Having the necessary skills and all the components, in a short time you will have a transformed corded screwdriver. To carry out the work you will need:
- charger from a screwdriver;
- old factory battery;
- soft multi-core electrical cable;
- soldering iron and solder;
- acids;
- insulating tape;
- power supply from a computer (or another).
Transformation options
Can be used various options power supplies to create a compact battery for uninterrupted operation of the screwdriver.
Battery or power supply from computer equipment
A device that supports the charge of a PC or laptop is quite suitable for achieving this goal. The process of introducing a power supply into a screwdriver is as follows:
- The screwdriver body is completely disassembled.
- The old power supply is removed and the wires are unsoldered.
- The wiring of the new unit is connected to the wiring of the old one, which powers the previous battery. When carrying out such an operation, it is important to observe polarity!
- Turn on the screwdriver and check for functionality. If all wires are connected correctly, the machine will work.
- There is a hole in the body of the device where a plug with a charging connector can easily be placed. By upgrading a screwdriver in this way, you get an improved device, which is now also recharged during operation like a laptop from a 220V network.
- The new power source is mounted inside the screwdriver, securing it with glue.
- The remaining body elements are returned to their place and the product is twisted, giving it its original appearance.
That's all! Now you know how to cordless screwdriver make it network.
Car battery as a power source
A car battery is an excellent option for remotely connecting a screwdriver to the network. To implement the idea, simply disconnect the clamps from the working tool and connect it to a power source.
Important! The use of such a source for long-term operation of a screwdriver is highly not recommended.
Using a welding inverter to power a screwdriver
To remake the old design, prepare a power supply circuit for a 12V screwdriver. The old design is improved to some extent by adding a secondary coil.
When compared with a computer battery, the advantage of the inverter is immediately noticeable. Thanks to the design features, it is immediately possible to determine the required voltage level and output current. This is an ideal method for those who live in radio engineering.
Features of corded screwdrivers
You can transform the device into a network device using another method, based on the production of a mobile station for recharging a screwdriver. An elastic wire is connected to the unit, to one end of which a plug is attached. Although, in order to operate such a station, you will need to build a special power supply or connect a ready-made transformer with a rectifier.
Important! Do not forget to ensure that the characteristics of the transformer match the parameters of the instrument.
If you are new to this business, then most likely it will be difficult for you to transform the coil with your own hands. Without having important skills, you can make a mistake with the number of turns or selection of wire diameter, so it is better to entrust such work to a specialist or at least a person who understands the topic.
90% of equipment is sold with a built-in transformer. All you need to do is select the best option and design a rectifier for it. To solder the rectifier bridge, semiconductor diodes are used, selected strictly according to the parameters of the tool.
Experts recommend following certain rules to everyone who decides to reconstruct a screwdriver and construct a 12V power supply for a screwdriver with their own hands. Instructions for upgrading the tool include the following tips:
- You can use a corded screwdriver as much as you like without worrying about the battery running out. However, such an instrument needs rest. Therefore, take five-minute breaks to avoid overheating or overloading the instrument.
- When working with a screwdriver, do not forget to secure the wire in the elbow area. This will make it more convenient to operate the device, and the cord will not interfere when screwing in screws.
- Carry out systematic cleaning of the screwdriver power supply from accumulations of dust and dirt deposits.
- The new battery is provided with grounding.
- Do not use more than one extension cord to connect to the network.
- This device is not recommended for use in high-altitude work (from two meters).
Now you know what power supply is needed for a 12V screwdriver, and what materials to use to make such a design yourself at home. There is no need to replace the old screwdriver with a new one. A radical decision should be made only if the unit is completely out of order, and a “dead” battery is not a problem for the craftsman. You just need to have an understanding of radio engineering and arm yourself with a soldering iron. Then it will be easier to cope with the task.
How to assemble a simple power supply and a powerful voltage source yourself.
Sometimes you have to connect various electronic devices, including homemade ones, to a 12 volt DC source. The power supply is easy to assemble yourself within half a weekend. Therefore, there is no need to purchase a ready-made unit, when it is more interesting to independently make the necessary thing for your laboratory. 
Anyone who wants to can make a 12-volt unit on their own, without much difficulty.
Some people need a source to power an amplifier, while others need a source to power a small TV or radio...
Step 1: What parts are needed to assemble the power supply...
To assemble the block, prepare in advance the electronic components, parts and accessories from which the block itself will be assembled....
-Circuit board.
-Four 1N4001 diodes, or similar. Diode bridge.
- Voltage stabilizer LM7812.
-Low-power step-down transformer for 220 V, the secondary winding should have 14V - 35V alternating voltage, with a load current from 100 mA to 1A, depending on how much power is needed at the output.
-Electrolytic capacitor with a capacity of 1000 µF - 4700 µF.
-Capacitor with a capacity of 1uF.
-Two 100nF capacitors.
-Cuttings of installation wire.
-Radiator, if necessary.
If you need to get maximum power from the power source, you need to prepare an appropriate transformer, diodes and a heatsink for the chip.
Step 2: Tools....
To make a block, you need the following installation tools:
-Soldering iron or soldering station
-Pliers
-Installation tweezers
- Wire strippers
-Device for solder suction.
-Screwdriver.
And other tools that may be useful.
Step 3: Diagram and others... 
To obtain 5 volt stabilized power, you can replace the LM7812 stabilizer with an LM7805.
To increase the load capacity to more than 0.5 amperes, you will need a heatsink for the microcircuit, otherwise it will fail due to overheating.
However, if you need to get several hundred milliamps (less than 500 mA) from the source, then you can do without a radiator, the heating will be negligible.
In addition, an LED has been added to the circuit to visually verify that the power supply is working, but you can do without it.
Power supply circuit 12V 30A.
When using one 7812 stabilizer as a voltage regulator and several powerful transistors, this power supply is capable of providing an output load current of up to 30 amperes.
Perhaps the most expensive part of this circuit is the power step-down transformer. The voltage of the secondary winding of the transformer must be several volts higher than the stabilized voltage of 12V to ensure the operation of the microcircuit. It must be borne in mind that you should not strive for a larger difference between the input and output voltage values, since at such a current the heat sink of the output transistors increases significantly in size.
In the transformer circuit, the diodes used must be designed for a high maximum forward current, approximately 100A. The maximum current flowing through the 7812 chip in the circuit will not be more than 1A.
Six composite Darlington transistors of the TIP2955 type connected in parallel provide a load current of 30A (each transistor is designed for a current of 5A), such a large current requires an appropriate size of the radiator, each transistor passes through one sixth of the load current.
A small fan can be used to cool the radiator.
Checking the power supply
When you turn it on for the first time, it is not recommended to connect a load. We check the functionality of the circuit: connect a voltmeter to the output terminals and measure the voltage, it should be 12 volts, or the value is very close to it. Next, we connect a 100 Ohm load resistor with a dissipation power of 3 W, or a similar load - such as an incandescent lamp from a car. In this case, the voltmeter reading should not change. If there is no 12 volt voltage at the output, turn off the power and check the correct installation and serviceability of the elements.
Before installation, check the serviceability of the power transistors, since if the transistor is broken, the voltage from the rectifier goes directly to the output of the circuit. To avoid this, check the power transistors for short circuits; to do this, use a multimeter to separately measure the resistance between the collector and emitter of the transistors. This check must be carried out before installing them in the circuit.
Power supply 3 - 24V
The power supply circuit produces an adjustable voltage in the range from 3 to 25 volts, with a maximum load current of up to 2A; if you reduce the current-limiting resistor to 0.3 ohms, the current can be increased to 3 amperes or more.
Transistors 2N3055 and 2N3053 are installed on the corresponding radiators; the power of the limiting resistor must be at least 3 W. Voltage regulation is controlled by an LM1558 or 1458 op amp. When using a 1458 op amp, it is necessary to replace the stabilizer elements that supply voltage from pin 8 to 3 of the op amp from a divider on resistors rated 5.1 K.
The maximum DC voltage for powering op-amps 1458 and 1558 is 36 V and 44 V, respectively. The power transformer must produce a voltage at least 4 volts higher than the stabilized output voltage. The power transformer in the circuit has an output voltage of 25.2 volts AC with a tap in the middle. When switching windings, the output voltage decreases to 15 volts.
1.5 V power supply circuit
The power supply circuit to obtain a voltage of 1.5 volts uses a step-down transformer, a bridge rectifier with a smoothing filter and an LM317 chip.
Diagram of an adjustable power supply from 1.5 to 12.5 V
Power supply circuit with output voltage regulation to obtain voltage from 1.5 volts to 12.5 volts; the LM317 microcircuit is used as a regulating element. It must be installed on the radiator, on an insulating gasket to prevent a short circuit to the housing.
Power supply circuit with fixed output voltage
Power supply circuit with a fixed output voltage of 5 volts or 12 volts. The LM 7805 chip is used as an active element, LM7812 is installed on a radiator to cool the heating of the case. The choice of transformer is shown on the left on the plate. By analogy, you can make a power supply for other output voltages.
20 Watt power supply circuit with protection
The circuit is intended for a small homemade transceiver, author DL6GL. When developing the unit, the goal was to have an efficiency of at least 50%, a nominal supply voltage of 13.8V, maximum 15V, for a load current of 2.7A.
Which scheme: switching power supply or linear?
Switching power supplies are small-sized and have good efficiency, but it is unknown how they will behave in a critical situation, surges in the output voltage...
Despite the shortcomings, a linear control scheme was chosen: a fairly large transformer, not high efficiency, cooling required, etc.
Parts from a homemade power supply from the 1980s were used: a radiator with two 2N3055. The only thing missing was a µA723/LM723 voltage regulator and a few small parts.
The voltage regulator is assembled on a µA723/LM723 microcircuit with standard inclusion. Output transistors T2, T3 type 2N3055 are installed on radiators for cooling. Using potentiometer R1, the output voltage is set within 12-15V. Using variable resistor R2, the maximum voltage drop across resistor R7 is set, which is 0.7V (between pins 2 and 3 of the microcircuit).
A toroidal transformer is used for the power supply (can be any at your discretion).
On the MC3423 chip, a circuit is assembled that is triggered when the voltage (surge) at the output of the power supply is exceeded, by adjusting R3 the voltage threshold is set on leg 2 from the divider R3/R8/R9 (2.6V reference voltage), the voltage that opens the thyristor BT145 is supplied from output 8, causing a short circuit leading to tripping of fuse 6.3a.
To prepare the power supply for operation (the 6.3A fuse is not yet involved), set the output voltage to, for example, 12.0V. Load the unit with a load; for this you can connect a 12V/20W halogen lamp. Set R2 so that the voltage drop is 0.7V (the current should be within 3.8A 0.7=0.185Ωx3.8).
We configure the operation of the overvoltage protection; to do this, we smoothly set the output voltage to 16V and adjust R3 to trigger the protection. Next, we set the output voltage to normal and install the fuse (before that we installed a jumper).
The described power supply can be reconstructed for more powerful loads; to do this, install a more powerful transformer, additional transistors, wiring elements, and a rectifier at your discretion.
Homemade 3.3v power supply
If you need a powerful power supply of 3.3 volts, then it can be made by converting an old power supply from a PC or using the above circuits. For example, replace a 47 ohm resistor of a higher value in the 1.5 V power supply circuit, or install a potentiometer for convenience, adjusting it to the desired voltage.
Transformer power supply on KT808
Many radio amateurs still have old Soviet radio components that are lying around idle, but which can be successfully used and they will serve you faithfully for a long time, one of the well-known UA1ZH circuits that is floating around the Internet. Many spears and arrows have been broken on forums when discussing what is better, a field-effect transistor or a regular silicon or germanium one, what temperature of crystal heating will they withstand and which one is more reliable?
Each side has its own arguments, but you can get the parts and make another simple and reliable power supply. The circuit is very simple, protected from overcurrent, and when three KT808 are connected in parallel, it can produce a current of 20A; the author used such a unit with 7 parallel transistors and delivered 50A to the load, while the filter capacitor capacity was 120,000 uF, the voltage of the secondary winding was 19V. It must be taken into account that the relay contacts must switch such a large current.
If installed correctly, the output voltage drop does not exceed 0.1 volt
Power supply for 1000V, 2000V, 3000V
If we need to have a high voltage DC source to power the transmitter output stage lamp, what should we use for this? On the Internet there are many different power supply circuits for 600V, 1000V, 2000V, 3000V.
First: for high voltage, circuits with transformers for both one phase and three phases are used (if there is a three-phase voltage source in the house).
Second: to reduce size and weight, they use a transformerless power supply circuit, directly a 220-volt network with voltage multiplication. The biggest drawback of this circuit is that there is no galvanic isolation between the network and the load, as the output is connected to a given voltage source, observing phase and zero.
The circuit has a step-up anode transformer T1 (for the required power, for example 2500 VA, 2400V, current 0.8 A) and a step-down filament transformer T2 - TN-46, TN-36, etc. To eliminate current surges during switching on and protection diodes when charging capacitors, switching is used through quenching resistors R21 and R22.
The diodes in the high-voltage circuit are shunted by resistors in order to uniformly distribute Urev. Calculation of the nominal value using the formula R(Ohm) = PIVx500. C1-C20 to eliminate white noise and reduce surge voltages. You can also use bridges like KBU-810 as diodes by connecting them according to the specified circuit and, accordingly, taking the required amount, not forgetting about shunting.
R23-R26 for discharging capacitors after a power outage. To equalize the voltage on series-connected capacitors, equalizing resistors are placed in parallel, which are calculated from the ratio for every 1 volt there are 100 ohms, but at high voltage the resistors turn out to be quite powerful and here you have to maneuver, taking into account that the open-circuit voltage is higher by 1, 41.
More on the topic
Transformer power supply 13.8 volts 25 A for a HF transceiver with your own hands.
Repair and modification of the Chinese power supply to power the adapter.
Details
Diode bridge at the input 1n4007 or a ready-made diode assembly designed for a current of at least 1 A and a reverse voltage of 1000 V.Resistor R1 is at least two watts, or 5 watts 24 kOhm, resistor R2 R3 R4 with a power of 0.25 watts.
Electrolytic capacitor on the high side 400 volts 47 uF.
Output 35 volts 470 – 1000 uF. Film filter capacitors designed for a voltage of at least 250 V 0.1 - 0.33 µF. Capacitor C5 – 1 nF. Ceramic, ceramic capacitor C6 220 nF, film capacitor C7 220 nF 400 V. Transistor VT1 VT2 N IRF840, transformer from an old computer power supply, diode bridge at the output full of four ultra-fast HER308 diodes or other similar ones.
In the archive you can download the circuit and board:
(downloads: 1157)
The printed circuit board is made on a piece of foil-coated single-sided fiberglass laminate using the LUT method. For ease of connecting power and connecting output voltage, the board has screw terminal blocks.
12 V switching power supply circuit
The advantage of this circuit is that this circuit is very popular of its kind and is repeated by many radio amateurs as their first switching power supply and efficiency and times more, not to mention size. The circuit is powered from a mains voltage of 220 volts; at the input there is a filter which consists of a choke and two film capacitors designed for a voltage of at least 250 - 300 volts with a capacity of 0.1 to 0.33 μF; they can be taken from a computer power supply.
In my case there is no filter, but it is advisable to install it. Next, the voltage is supplied to a diode bridge designed for a reverse voltage of at least 400 Volts and a current of at least 1 Ampere. You can also supply a ready-made diode assembly. Next in the diagram there is a smoothing capacitor with an operating voltage of 400 V, since the amplitude value of the mains voltage is around 300 V. The capacitance of this capacitor is selected as follows, 1 μF per 1 Watt of power, since I am not going to pump large currents out of this block, then in my case, the capacitor is 47 uF, although such a circuit can pump out hundreds of watts. The power supply for the microcircuit is taken from the alternating voltage, here a power source is arranged, resistor R1, which provides current damping, it is advisable to set it to a more powerful one of at least two watts since it is heated, then the voltage is rectified by just one diode and goes to a smoothing capacitor and then to the microcircuit. Pin 1 of the microcircuit is plus power and pin 4 is minus power.
You can assemble a separate power source for it and supply it with 15 V according to the polarity. In our case, the microcircuit operates at a frequency of 47 - 48 kHz. For this frequency, an RC circuit is organized consisting of a 15 kohm resistor R2 and a 1 nF film or ceramic capacitor. With this arrangement of parts, the microcircuit will work correctly and produce rectangular pulses at its outputs, which are supplied to the gates of powerful field switches through resistors R3 R4, their values can deviate from 10 to 40 Ohms. Transistors must be installed N channel, in my case they are IRF840 with a drain-source operating voltage of 500 V and a maximum drain current at a temperature of 25 degrees of 8 A and a maximum power dissipation of 125 Watts. Next according to the diagram is pulse transformer, after it there is a full-fledged rectifier of four diodes of the HER308 brand, ordinary diodes are not suitable here since they cannot operate at high frequencies, so we install ultra-fast diodes and after the bridge the voltage is already supplied to the output capacitor 35 Volt 1000 μF, or 470 μF especially Large capacities are not required in switching power supplies.
Let's return to the transformer, it can be found on the boards of computer power supplies, it is not difficult to identify it; in the photo you can see the largest one, and that is what we need. To rewind such a transformer, you need to loosen the glue that glues the halves of the ferrite together; to do this, take a soldering iron or a soldering iron and slowly warm up the transformer, you can put it in boiling water for a few minutes and carefully separate the halves of the core. We wind up all the basic windings, and we will wind our own. Based on the fact that I need to get a voltage of around 12-14 Volts at the output, the primary winding of the transformer contains 47 turns of 0.6 mm wire in two cores, we make insulation between the windings with ordinary tape, the secondary winding contains 4 turns of the same wire in 7 cores . It is IMPORTANT to wind in one direction, insulate each layer with tape, marking the beginning and end of the windings, otherwise nothing will work, and if it does, then the unit will not be able to deliver all the power.
Block check
Well, now let's test our power supply, since my version is completely working, I immediately connect it to the network without a safety lamp.Let's check the output voltage as we see it is around 12 - 13 V and does not fluctuate much due to voltage drops in the network.
As a load, a 12 V car lamp with a power of 50 Watts flows a current of 4 A. If such a unit is supplemented with current and voltage regulation, and an input electrolyte of a larger capacity is supplied, then you can safely assemble a car charger and a laboratory power supply.
Before starting the power supply, you need to check the entire installation and connect it to the network through a 100-watt incandescent safety lamp; if the lamp burns at full intensity, then look for errors when installing the snot; the flux has not been washed off or some component is faulty, etc. When assembled correctly, the lamp should be slightly flash and go out, this tells us that the input capacitor is charged and there are no errors in the installation. Therefore, before installing components on the board, they must be checked, even if they are new. Another important point after startup is that the voltage on the microcircuit between pins 1 and 4 must be at least 15 V. If this is not the case, you need to select the value of resistor R2.
We present a powerful stabilized 12 V power supply. It is built on an LM7812 stabilizer chip and TIP2955 transistors, which provides a current of up to 30 A. Each transistor can provide a current of up to 5 A, respectively, 6 transistors will provide a current of up to 30 A. You can change the number of transistors and get desired current value. The microcircuit produces a current of about 800 mA.
A 1 A fuse is installed at its output to protect against large transient currents. It is necessary to ensure good heat dissipation from transistors and the microcircuit. When the current through the load is large, the power dissipated by each transistor also increases, so that excess heat can cause the transistor to fail.
In this case, a very large radiator or fan will be required for cooling. 100 ohm resistors are used for stability and to prevent saturation as... the gain factors have some scatter for the same type of transistors. The bridge diodes are designed for at least 100 A.
Notes
The most expensive element of the entire design is perhaps the input transformer. Instead, it is possible to use two series-connected car batteries. The voltage at the input of the stabilizer must be a few volts higher than the required output (12V) so that it can maintain a stable output. If a transformer is used, the diodes must be able to withstand a fairly large peak forward current, typically 100A or more.
No more than 1 A will pass through LM 7812, the rest is provided by transistors. Since the circuit is designed for a load of up to 30 A, six transistors are connected in parallel. The power dissipated by each of them is 1/6 of the total load, but it is still necessary to ensure sufficient heat dissipation. Maximum load current will result in maximum dissipation and will require a large heatsink.
To effectively remove heat from the radiator, it may be a good idea to use a fan or water-cooled radiator. If the power supply is loaded to its maximum load, and the power transistors fail, then all the current will pass through the chip, which will lead to a catastrophic result. To prevent breakdown of the microcircuit, there is a 1 A fuse at its output. The 400 MOhm load is for testing only and is not included in the final circuit.
Computations
This diagram is an excellent demonstration of Kirchhoff's laws. The sum of currents entering a node must be equal to the sum of currents leaving this node, and the sum of the voltage drops on all branches of any closed circuit circuit must be equal to zero. In our circuit, the input voltage is 24 volts, of which 4V drops across R7 and 20 V at the input of LM 7812, i.e. 24 -4 -20 = 0. At the output, the total load current is 30A, the regulator supplies 0.866A and 4.855A each 6 transistors: 30 = 6 * 4.855 + 0.866.
The base current is about 138mA per transistor to get a collector current of about 4.86A gain DC for each transistor there must be at least 35.
TIP2955 meets these requirements. The voltage drop across R7 = 100 Ohm at maximum load will be 4V. The power dissipated on it is calculated by the formula P= (4 * 4) / 100, i.e. 0.16 W. It is desirable that this resistor be 0.5 W.
The input current of the microcircuit comes through the resistor in the emitter circuit and the junction B-E transistors. Let's apply Kirchhoff's laws once again. The regulator input current consists of 871 mA current flowing through the base circuit and 40.3 mA through R = 100 Ohms.
871.18 = 40.3 + 830. 88. The input current of the stabilizer must always be greater than the output current. We can see that it only consumes about 5 mA and should barely get warm.
Testing and Bugs
During the first test, there is no need to connect the load. First, we measure the output voltage with a voltmeter; it should be 12 volts, or a value not very different. Then we connect a resistance of about 100 Ohms, 3 W as a load. The voltmeter readings should not change. If you do not see 12 V, then, after turning off the power, you should check the correctness of installation and the quality of soldering.
One of the readers received 35 V at the output, instead of the stabilized 12 V. This was caused by a short circuit in the power transistor. If there is a short circuit in any of the transistors, you will have to unsolder all 6 to check the collector-emitter transitions with a multimeter.
So the next device has been assembled, now the question arises: what to power it from? Batteries? Batteries? No! The power supply is what we will talk about.
Its circuit is very simple and reliable, it has short-circuit protection and smooth adjustment of the output voltage.
A rectifier is assembled on the diode bridge and capacitor C2, circuit C1 VD1 R3 is a reference voltage stabilizer, circuit R4 VT1 VT2 is a current amplifier for power transistor VT3, protection is assembled on transistor VT4 and R2, and resistor R1 is used for adjustment.
I took the transformer from an old charger from a screwdriver, at the output I got 16V 2A
As for the diode bridge (at least 3 amperes), I took it from an old ATX block as well as electrolytes, a zener diode, and resistors.
I used a 13V zener diode, but the Soviet D814D is also suitable.
The transistors were taken from an old Soviet TV; transistors VT2, VT3 can be replaced with one component, for example KT827.
Resistor R2 is a wirewound with a power of 7 Watts and R1 (variable) I took nichrome for adjustment without jumps, but in its absence you can use a regular one.
It consists of two parts: the first one contains the stabilizer and protection, and the second one contains the power part.
All parts are mounted on the main board (except for power transistors), transistors VT2, VT3 are soldered onto the second board, we attach them to the radiator using thermal paste, there is no need to insulate the housing (collectors). The circuit was repeated many times and does not need adjustment. Photos of two blocks are shown below with a large 2A radiator and a small 0.6A.
Indication
Voltmeter: for it we need a 10k resistor and a 4.7k variable resistor and I took an indicator m68501, but you can use another one. From resistors we will assemble a divider, a 10k resistor will prevent the head from burning out, and with a 4.7k resistor we will set the maximum deviation of the needle.
After the divider is assembled and the indication is working, you need to calibrate it; to do this, open the indicator and glue clean paper onto the old scale and cut it along the contour; it is most convenient to cut the paper with a blade.
When everything is glued and dry, we connect the multimeter in parallel to our indicator, and all this to the power supply, mark 0 and increase the voltage to volts, mark, etc.
Ammeter: for it we take a resistor of 0.27 ohm!!! and variable at 50k, The connection diagram is below, using a 50k resistor we will set the maximum deviation of the arrow.
The graduation is the same, only the connection changes, see below; a 12 V halogen light bulb is ideal as a load.
List of radioelements
| Designation | Type | Denomination | Quantity | Note | Shop | My notepad |
|---|---|---|---|---|---|---|
| VT1 | Bipolar transistor | KT315B | 1 | To notepad | ||
| VT2, VT4 | Bipolar transistor | KT815B | 2 | To notepad | ||
| VT3 | Bipolar transistor | KT805BM | 1 | To notepad | ||
| VD1 | Zener diode | D814D | 1 | To notepad | ||
| VDS1 | Diode bridge | 1 | To notepad | |||
| C1 | 100uF 25V | 1 | To notepad | |||
| C2, C4 | Electrolytic capacitor | 2200uF 25V | 2 | To notepad | ||
| R2 | Resistor | 0.45 Ohm | 1 | To notepad | ||
| R3 | Resistor | 1 kOhm | 1 | To notepad | ||
| R4 | Resistor |