LEDs are replacing types of light sources such as fluorescent and incandescent lamps. Almost every home already has LED lamps; they consume much less than their two predecessors (up to 10 times less than incandescent lamps and 2 to 5 times less than CFLs or energy-saving fluorescent lamps). In situations where a long light source is needed, or it is necessary to organize illumination of a complex shape, it is used.
LED strip is ideal for a number of situations; its main advantage over individual LEDs and LED matrices is power supplies. They are easier to find for sale in almost any electrical goods store, unlike drivers for high-power LEDs, and besides, the selection of a power supply is carried out only by power consumption, because The vast majority of LED strips have a supply voltage of 12 Volts.
While for high-power LEDs and modules, when choosing a power source, you need to look for a current source with the required power and rated current, i.e. take into account 2 parameters, which complicates the selection.
This article discusses typical power supply circuits and their components, as well as tips for repairing them for novice radio amateurs and electricians.
Types and requirements for power supplies for LED strips and 12 V LED lamps
The main requirement for a power source for both LEDs and LED strips is high-quality voltage/current stabilization, regardless of mains voltage surges, as well as low output ripple.
Based on the type of design, power supplies for LED products are divided into:
Sealed. They are more difficult to repair; the body cannot always be carefully disassembled, and the inside may even be filled with sealant or compound.
Non-hermetic, for indoor use. Better amenable to repair, because... The board is removed after unscrewing several screws.
By cooling type:
Passive air. The power supply is cooled due to natural air convection through the perforations of its housing. Disadvantage is the inability to achieve high power while maintaining weight and size indicators;
Active air. The power supply is cooled using a cooler (a small fan, as installed on PC system units). This type of cooling allows you to achieve more power in the same size with a passive power supply.
Power supply circuits for LED strips
It is worth understanding that in electronics there is no such thing as a “power supply for an LED strip”; in principle, any power supply with a suitable voltage and a current greater than that consumed by the device will be suitable for any device. This means that the information described below applies to almost any power supply.
However, in everyday life it is easier to talk about a power supply according to its purpose for a specific device.
General structure of a switching power supply
Switching power supplies (UPS) have been used to power LED strips and other equipment for the last decades. They differ from transformer ones in that they operate not at the frequency of the supply voltage (50 Hz), but at high frequencies (tens and hundreds of kilohertz).
Therefore, for its operation, a high-frequency generator is needed; in cheap power supplies designed for low currents (units of amperes), a self-oscillator circuit is often found; it is used in:
electronic transformers;
electronic ballasts for fluorescent lamps;
mobile phone chargers;
cheap UPS for LED strips (10-20 W) and other devices.
A diagram of such a power supply can be seen in the figure (click on the picture to enlarge):
Its structure is as follows:
The OS includes an optocoupler U1, with its help the power part of the oscillator receives a signal from the output and maintains a stable output voltage. There may be no voltage in the output part due to a break in the VD8 diode, often this is a Schottky assembly and must be replaced. A swollen electrolytic capacitor C10 also often causes problems.
As you can see, everything works with a much smaller number of elements, the reliability is appropriate...
More expensive power supplies
The circuits that you will see below are often found in power supplies for LED strips, DVD players, radio tape recorders and other low-power devices (tens of watts).
Before moving on to considering popular circuits, familiarize yourself with the structure of a switching power supply with a PWM controller.
The upper part of the circuit is responsible for filtering, rectifying and smoothing ripples of the mains voltage 220, essentially similar to both the previous type and the subsequent ones.
The most interesting thing is the PWM block, the heart of any decent power supply. A PWM controller is a device that controls the duty cycle of an output signal based on a user-defined setpoint or current or voltage feedback. PWM can control both load power using a field (bipolar, IGBT) switch, and a semiconductor controlled switch as part of a converter with a transformer or inductor.
By changing the width of the pulses at a given frequency, you also change the effective value of the voltage, while maintaining the amplitude, you can integrate it using C- and LC-circuits to eliminate ripple. This method is called Pulse Width Modeling, that is, modeling a signal using the pulse width (duty factor/duty factor) at a constant frequency.
In English it sounds like a PWM-controller, or Pulse-Width Modulation controller.
The figure shows bipolar PWM. Rectangular signals are control signals on transistors from the controller; the dotted line shows the shape of the voltage in the load of these switches - the effective voltage.
Higher-quality low-average power supplies are often built on integrated PWM controllers with a built-in power switch. Advantages over self-oscillator circuit:
The operating frequency of the converter does not depend on either the load or the supply voltage;
Better stabilization of output parameters;
Possibility of simpler and more reliable adjustment of the operating frequency at the stage of design and modernization of the unit.
Below are several typical power supply circuits (click on the picture to enlarge):
Here RM6203 is both a controller and a key in one housing.
The same thing, but on a different chip.
Feedback is carried out using a resistor, sometimes an optocoupler connected to an input called Sense (sensor) or Feedback (feedback). Repair of such power supplies is generally similar. If all the elements are working properly, and the supply voltage is supplied to the microcircuit (Vdd or Vcc leg), then the problem is most likely in it, more accurately looking at the output signals (drain, gate leg).
Almost always, you can replace such a controller with any analogue with a similar structure; to do this, you need to check the datasheet against the one installed on the board and the one you have and solder it, observing the pinout, as shown in the following photographs.
Or here is a schematic representation of the replacement of such microcircuits.
Powerful and expensive power supplies
Power supplies for LED strips, as well as some power supplies for laptops, are made on the UC3842 PWM controller.
The scheme is more complex and reliable. The main power component is transistor Q2 and transformer. During repairs, you need to check the filtering electrolytic capacitors, the power switch, Schottky diodes in the output circuits and output LC filters, the supply voltage of the microcircuit, otherwise the diagnostic methods are similar.
However, more detailed and accurate diagnostics are only possible using an oscilloscope; otherwise, checking for short circuits on the board, soldering of elements and breaks will cost more. Replacing suspicious nodes with known working ones can help.
More advanced models of power supplies for LED strips are made on the almost legendary TL494 chip (any letters with the numbers “494”) or its analogue KA7500. By the way, most AT and ATX computer power supplies are built on these same controllers.
Here is a typical power supply diagram for this PWM controller (click on the diagram):
Such power supplies are highly reliable and stable.
Brief verification algorithm:
1. We power the microcircuit according to the pinout from an external power source of 12-15 volts (12 leg is plus, and 7 leg is minus).
2. A voltage of 5 Volts should appear on the 14 legs, which will remain stable when the power supply changes; if it “floats” - the microcircuit needs to be replaced.
3. There should be a sawtooth voltage at pin 5; you can “see” it only with the help of an oscilloscope. If it is not there or the shape is distorted, we check compliance with the nominal values of the timing RC circuit, which is connected to pins 5 and 6; if not, in the diagram these are R39 and C35, they must be replaced; if nothing has changed after that, the microcircuit has failed.
4. There should be rectangular pulses at outputs 8 and 11, but they may not exist due to the specific feedback implementation circuit (pins 1-2 and 15-16). If you turn off and connect 220 V, they will appear there for a while and the unit will go into protection again - this is a sign of a working microcircuit.
5. You can check the PWM by short-circuiting the 4th and 7th legs, the pulse width will increase, and short-circuiting the 4th to 14th legs, the pulses will disappear. If you get different results, the problem is in MS.
This is the most brief test of this PWM controller; there is a whole book about repairing power supplies based on them, “Switching Power Supplies for IBM PC.”
Although it is dedicated to computer power supplies, there is a lot of useful information for any radio amateur.
Conclusion
The circuitry of power supplies for LED strips is similar to any power supplies with similar characteristics; they can be repaired, modernized, and adjusted to the required voltages quite well, of course, within reasonable limits.
To connect consumers of electrical energy in Russia, current standards provide for an alternating current network of 220/380V 50Hz. Since LED strips are powered from a pulsed stabilized source with a voltage of 24 or 12V, a device is needed that converts high alternating voltage to a lower one.
Successfully copes with this task power supply for LED strip (PSU) . The stability and duration of the backlight is ensured by a competent choice of power supply.
Any of the commercially available models allows operation of the backlight over a wide temperature range, smoothes out impulse noise well, and has a housing that protects internal elements from mechanical damage.
Connecting power to an LED strip with your own hands is not that difficult. The main thing is to strictly follow the advice outlined below.
Before purchasing one or another rectifier model, you need to understand the question of how to connect the LED strip to the power supply.
LED strips can be connected to a power source in various ways. If the power supply circuit for LED strips is strictly followed, even one powerful device can provide operation of both one and several backlights.
For the uninterrupted operation of a circuit using one power supply, it is important to comply with the condition - the power of the unit must be at least 30% greater than the total load.
To connect a second LED strip in parallel to one block you will need additional extension cord- a wire with a cross-section of at least 1.5 mm. Observing the polarity, one end of it is connected to the output of the power supply, the second to strip No. 2. In this case, the current will be supplied not through the tracks of the first backlight, but through the connected wire.
When the use of a large, powerful power supply is unacceptable, low-power power supplies for 12-volt LED strips are used. The connection diagram provides for the presence separate power supply for each strip of diodes. Here you will also need extension- a wire connected to a 220 V network and to a specific tape, but its cross-section may be smaller - 0.75 mm is enough. Although in this case the installation is more complex, a similar connection diagram is often used in practice, since it involves the use of small-sized power supplies.
The location for the power supply is selected taking into account:
A large, powerful power supply for an LED strip in an apartment is difficult to make invisible - it is necessary to equip a special niche.
Suitable options for placing a large power supply may be a specially made hole in the furniture or a separate shelf on the wall, equipped on the non-visible side of the table.
In case of small-sized power supplies(no more than 250x150x100 mm) everything is much simpler:
Unsealed or open 100 W units are used to power consumers in closed residential and non-residential premises. Devices of this type are easy to identify: as a rule, they differ largest size and weight, are appropriately marked IP20.
The walls of the housing are perforated to ensure heat dissipation and are made of plastic or sheet metal. Scope of application: equipment power supply. Placement: special cabinets or hardware niches.
It should be remembered that unsealed devices are not protected from moisture, so they are not recommended for use in rooms with high humidity, for example, in bathrooms.
Semi-hermetic (all-weather) power supplies can be classified as a universal device. The devices are used both indoors and outdoors. The unit is used to power a 12V LED strip, has a degree of protection IP54 and a sheet metal housing.
The best solution today is sealed power supply for LED strip with plastic housing . The power of the device does not exceed 75 W, it is completely protected from moisture, and has small dimensions and weight. Even using two 50 W power supplies of this type to power two LED strips, they can be easily hidden from human eyes in any corner of the room. Place of application: interior lighting.
The power of the power supply for the LED strip depends on the load connected to it. If for small consumers a 40 W power supply is sufficient, then for more substantial designs you may need a device whose power reaches 0.5 kW.
To correctly calculate the power of a power supply, you need to know:
1. Determining the total load. To do this, multiply the power consumption of 1 meter by the meter of the LED strip.
2. To accurately calculate the power of the power supply We multiply the total load by the safety factor kз.
Pbp = Ptot × kz
Since the connection diagram contains an element such as RGB controller, the final parameter of the power supply unit is determined taking into account the power of the controller - its value usually does not exceed 5 W.
Modern industry offers consumers a wide selection of power supplies for connecting LED strips. The power supply for connecting groups of LEDs is selected taking into account the parameters of the voltage required for the backlight to operate (12 or 24 V, respectively), the required power and the place of operation.
Model PV-15.
The lowest-power switching power supply for a 12V LED strip with a power of 15 W is used to connect a strip designed for a voltage of 12 volts. It has a waterproof aluminum case and a built-in surge protector that protects against voltage surges. The estimated operating time exceeds 200 thousand hours. The best option for outdoor placement. The price of the product is 560 rubles. a piece.
Model PV-40.
The design is similar to PV-15 with increased power parameters - 40 W. Designed for connecting LED strips operating on 24/12 volts. PV-40 - LED strip unit priced within 1000 rubles.
Model LV-50.
The design feature is a sealed plastic case. The switching power supply has protection against voltage surges and short circuits in the network and is intended for use in outdoor conditions.
The built-in surge filter ensures stable operation of the unit in Russian electrical networks. Operates at temperatures from minus 25 to plus 40 degrees Celsius. Operating time - more than 200 thousand hours. The price of the product is 1050 rubles.
Model LPV-100.
Medium power switching power supply - 100 W. Designed for connecting tapes with a voltage of 24/12 volts, has a sealed design and an aluminum housing. The product is characterized by protection against overvoltage, overload, short circuit. Ideal for stable operation in Russian electrical networks. The estimated period of operation is more than 200 thousand hours. LPV-100 is a high-quality power supply for LED strip, the price of which does not exceed 2250 rubles.
Model SUN-400.
A high-power switching power supply is an excellent solution for ensuring the operation of LED strips. Has protection against short circuits and voltage surges. The cooling principle is free air convection. Provides operation of tapes designed for 24/12 volt voltage in enclosed spaces, power - 400 W. Successfully passed performance tests in Russian electrical networks. The price of the product is 3600 rubles.
Switching power supplies (SMPS) are usually quite complex devices, which is why novice radio amateurs tend to avoid them. However, thanks to the proliferation of specialized integrated PWM controllers, it is possible to construct designs that are quite simple to understand and repeat, with high power and efficiency. The proposed power supply has a peak power of about 100 W and is built according to the flyback topology (flyback converter), and the control element is the CR6842S microcircuit (pin-compatible analogues: SG6842J, LD7552 and OB2269).
Attention! In some cases, you may need an oscilloscope to debug the circuit!
On Ali it is easy to find many options for ready-made blocks according to this scheme, for example, by queries like "Artillery power supply 24V 3A", "Power supply XK-2412-24", "Eyewink 24V switching power supply" and the like. On amateur radio portals this model has already been dubbed “folk” due to its simplicity and reliability. Circuitry options 12V and 24V differ slightly and have an identical topology.
Example of a finished power supply from Ali:
Note! In this power supply model, the Chinese have a very high percentage of defects, so when purchasing a finished product, before turning it on, it is advisable to carefully check the integrity and polarity of all elements. In my case, for example, the VD2 diode had the wrong polarity, which is why after three starts the unit burned out and I had to change the controller and key transistor.
The methodology for designing SMPS in general, and this particular topology in particular, will not be considered here in detail, due to the too large amount of information - see separate articles.
Switching power supply with a power of 100W on the CR6842S controller.
| F 1 | Regular fuse. |
| 5D-9 | The thermistor limits the current surge when the power supply is turned on. At room temperature, it has a small resistance, which limits current surges; when current flows, it heats up, which causes a decrease in resistance, and therefore does not subsequently affect the operation of the device. |
| C 1 | Input capacitor to suppress asymmetrical noise. It is permissible to increase the capacitance slightly; it is desirable that it be an interference suppression capacitor like X2 or had a large (10-20 times) margin of operating voltage. For reliable interference suppression, it must have low ESR and ESL. |
| L 1 | Common mode filter to suppress symmetrical interference. It consists of two inductors with the same number of turns, wound on a common core and connected in phase. |
| KBP307 | Rectifier diode bridge. |
| R5, R9 | Circuit required to run CR6842. Through it, the primary charge of capacitor C 4 is carried out to 16.5V. The circuit must provide a trigger current of at least 30 µA (maximum, according to the datasheet) over the entire input voltage range. Also, during operation, this chain controls the input voltage and compensates for the voltage at which the key closes - an increase in the current flowing into the third pin causes a decrease in the threshold voltage for closing the key. |
| R 10 | Timing resistor for PWM. Increasing the value of this resistor will reduce the switching frequency. The nominal value should be in the range of 16-36 kOhm. |
| C 2 | Smoothing capacitor. |
| R 3, C 7, VD 2 | A snubber circuit that protects the key transistor from reverse emissions from the primary winding of the transformer. It is advisable to use R 3 with a power of at least 1W. |
| C 3 | A capacitor that shunts the interwinding capacitance. Ideally, it should be Y-type, or it should have a large margin (15-20 times) of operating voltage. Serves to reduce interference. The rating depends on the parameters of the transformer; it is undesirable to make it too large. |
| R 6, VD 1, C 4 | This circuit, powered from the auxiliary winding of the transformer, forms the controller’s power circuit. This circuit also affects the operating cycle of the key. It works as follows: for correct operation, the voltage at the seventh pin of the controller must be in the range of 12.5 - 16.5 V. The voltage of 16.5 V at this pin is the threshold at which the key transistor opens and energy begins to be stored in the transformer core (at this time the microcircuit is powered from C 4). When it drops below 12.5V, the microcircuit turns off, so capacitor C 4 must provide power to the controller until energy is supplied from the auxiliary winding, so its rating should be sufficient to keep the voltage above 12.5V while the key is open. The lower limit of the C 4 rating should be calculated based on the controller consumption of about 5 mA. The time of the private key depends on the charging time of this capacitor to 16.5V and is determined by the current that the auxiliary winding can supply, while the current is limited by resistor R 6 . Among other things, through this circuit the controller provides overvoltage protection in the event of failure of the feedback circuits - if the voltage exceeds 25V, the controller will turn off and will not start working until the power from the seventh pin is removed. |
| R 13 | Limits the gate charge current of the key transistor and also ensures its smooth opening. |
| VD 3 | Transistor gate protection. |
| R 8 | Pulling the shutter to the ground performs several functions. For example, if the controller is turned off and the internal pull-up is damaged, this resistor will ensure rapid discharge of the transistor gate. Also, with correct board layout, it will provide a shorter gate discharge current path to ground, which should have a positive effect on noise immunity. |
| BT 1 | Key transistor. Installed on the radiator through an insulating gasket. |
| R 7, C 6 | The circuit serves to smooth out voltage fluctuations across the current-measuring resistor. |
| R 1 | Current measuring resistor. When the voltage on it exceeds 0.8V, the controller closes the key transistor, thus regulating the open key time. In addition, as mentioned above, the voltage at which the transistor will be closed also depends on the input voltage. |
| C 8 | Feedback optocoupler filter capacitor. It is permissible to increase the denomination a little. |
| PC817 | Opto-isolation of the feedback circuit. If the optocoupler transistor closes, this will cause an increase in voltage at the second terminal of the controller. If the voltage on the second pin exceeds 5.2V for longer than 56 ms, this will cause the key transistor to close. This provides protection against overload and short circuit. |
In this circuit, the 5th pin of the controller is not used. However, according to the datasheet for the controller, you can attach an NTC thermistor to it, which will ensure that the controller turns off in case of overheating. The stabilized output current of this pin is 70 μA. The temperature protection response voltage is 1.05V (the protection will turn on when the resistance reaches 15 kOhm). The recommended thermistor rating is 26 kOhm (at 27°C).
It should be remembered that one of the most important rules when designing is the correspondence between the overall power of the transformer and the output power of the power supply, so first of all, in any case, choose cores that are suitable for your task.
Most often, this design is supplied with transformers made on cores of type EE25 or EE16, or similar. It was not possible to collect enough information on the number of turns in this SMPS model, since different modifications, despite similar circuits, use different cores.
An increase in the difference in the number of turns leads to a reduction in switching losses of the key transistor, but increases the requirements for its load capacity in terms of maximum drain-source voltage (VDS).
For example, we will focus on standard cores of type EE25 and the maximum induction value Bmax = 300 mT. In this case, the ratio of turns of the first-second-third winding will be equal to 90:15:12.
It should be remembered that the indicated turns ratio is not optimal and the ratios may need to be adjusted based on test results.
The primary winding should be wound with a conductor no thinner than 0.3 mm in diameter. It is advisable to make the secondary winding with a double wire with a diameter of 1 mm. A small current flows through the auxiliary third winding, so a wire with a diameter of 0.2 mm will be quite sufficient.
| VD 4 | Dual rectifier diode. Ideally, select one with a voltage/current margin and a minimum drop. Installed on the radiator through an insulating gasket. |
| R 2 , C 12 | Snubber circuit to facilitate diode operation. It is advisable to use R2 with a power of at least 1W. |
| C 13, L 2, C 14 | Output filter. |
| C 20 | Ceramic capacitor, RF output shunt capacitor C 14. |
| R 17 | Load resistor providing no-load load. It also discharges the output capacitors in the event of startup and subsequent shutdown without load. |
| R 16 | Current limiting resistor for LED. |
| C 9, R 20, R 18, R 19, TLE431, PC817 | Feedback circuit on a precision power supply. Resistors set the operating mode of the TLE431, and PC817 provides galvanic isolation. |
If in your outlets the ground wire is connected to a good ground (and not simply not connected to anything, as is often the case), you can add two additional Y-capacitors, each connected to its own power wire and ground, between L 1 and the input capacitor C 1. This will ensure balancing of the potentials of the network wires relative to the housing and better suppression of the common-mode component of the interference. Together with the input capacitor, two additional capacitors form the so-called. "protective triangle".
After L 1 it is also worth adding another X-type capacitor, with the same capacity as C 1.
To protect against high-amplitude surge voltages, it is advisable to connect a varistor (for example, 14D471K) in parallel with the input. Also, if you have ground, for protection in the event of an accident on the power supply line, in which instead of phase and zero, phase falls on both wires, it is advisable to create a protective triangle of the same varistors.
Again, if there is a ground wire, it is advisable to add two more Y-capacitors of small capacity to the output of the block, connected according to the “protective triangle” circuit in parallel with C 14.
To quickly discharge capacitors when the device is turned off, it is advisable to add a megaohm resistor in parallel to the input circuits.
It is advisable to shunt each electrolytic capacitor via RF with small-capacity ceramics located as close as possible to the capacitor terminals.
It would be a good idea to also install a limiting TVS diode at the output - to protect the load from possible overvoltages in case of problems with the unit. For the 24V version, for example 1.5KE24A is suitable.
Power supply IMPROVEMENT OF POWER Commercially available Chinese-made power supplies for several voltages when connected to a player or receiver produce a large background of alternating current, since the filter after the diode bridge contains only a 470 uF electrolytic capacitor. I propose a simple modification to the block, which significantly reduces the level of pulsation. Additional parts are placed in the body of the block itself. advanced does not require any special explanation. It is advisable to install the transistor on a small radiator made of a piece of tin. Voltage switch SB1, after modifying the circuit, gives levels “shifted” by 1.5V. If desired, you can resolder the conductors suitable for SB1 and recreate the correspondence between those indicated on the switch and the output voltages, but then there will be no upper limit (12 V). O. KLEVTSOV, 320129, Dnepropetrovsk, Sholokhov street, 19 - 242. (RL-7/96)...
Amateur radio equipment components SMOOTH FREQUENCY ADJUSTMENT GENERATOR FOR P134 Discrete frequency setting in 1 kHz steps in the P134 radio station makes it difficult to use for amateur radio purposes. It is quite simple to obtain the probability of smooth frequency tuning up to ±4 kHz relative to the tuning frequency on the digital scale of the radio station. To do this, it is enough to change the signal with a frequency of 10 MHz supplied from the radio frequency synthesizer (block 2-1) through the multiplier block 3-3 per mixer block 3-1, by a signal of a quartz oscillator with a frequency of 10 MHz tunable up to ±500 Hz according to the circuit shown in Fig. 1.Puc.1 Since in a mixer block 3-1 the eighth harmonic of the generator is used, the operating frequency of the radio station will vary within ±4 kHz, which is completely sufficient. Resistor R7 in the circuit is selected within 0.5...2 kOhm, depending on the activity of the quartz used, until the nominal signal level is obtained at the output of the radio station when the key is pressed in AT-T mode. Zu for horse racing circuit Coil L is made on a ring magnetic circuit of brand 50VCh2 of standard size K7x4x2 with PELSHO wire 0.1 mm and contains 15 turns. Using a well-calibrated receiver, it is advisable to select the number of coil turns with an accuracy of one to obtain a generator frequency of 10 MHz ± 50 Hz in the middle position of the R4 regulator, while the operating frequency of the radio station will correspond to the frequency on the digital scale. It is advisable to use a quartz resonator in a vacuum version. The generator can be powered with a voltage of +12.6 V from capacitors C2...C6 of the decoupling filter in the power circuit block 2, which can be accessed by removing the top block N9 radio station. The printed circuit board of the device is shown in Fig. 2, the location of the parts on it is shown in Fig. 3. The board is conveniently placed in a shielded cassette unit with dimensions of 140x70x30 mm, mounted on the radio body to the left of the operator. On the face...
Nowadays, many people have players from various companies. All of them are powered by finger-type batteries. These batteries have a small capacity and quickly run out when using the player. Therefore, in stationary conditions, it is better to power players from the mains via a power supply, since the price of batteries these days is “biting”. In the radio engineering literature there are descriptions of various power supplies for radio devices, including for players with 3-volt power supply. The block described below provides an output voltage of 3 V with a load current of up to 400 mA, which is completely sufficient to power any player or radio. For this block power supply uses a transformer and a housing from block power supply for a microcalculator type MK-62 (“Electronics D2-10m”). The primary (network) winding is left at the transformer, and the secondary winding is rewound. Now it contains 270 turns of PEL or PEV 0.23 wire. ...
To operate a TV, computer, or radio, a stabilized power supply is required. Devices connected to the network around the clock, as well as circuits assembled by a novice radio amateur, require absolutely reliable power supply (BP) so that there is no damage to the circuit or fire of the power supply. And now a few “horror” stories: one of my friends, when a control transistor broke down, lost many microcircuits in a homemade computer; in another, after shorting the wires going to an imported radiotelephone with a chair leg, the power supply melted; the third has the same thing with the power supply of a “Soviet” industrial TA with caller ID; for a novice radio amateur, after a short circuit, the power supply began to deliver high voltage to the output; In production, a short circuit in a line of measuring instruments almost certainly leads to a stoppage of work and the need for urgent repairs. We will not touch upon the circuits of pulse blocks due to their complexity and low reliability, but will consider the circuit of a compensatory serial power regulator (Fig. 1). ...
Power supply Laboratory power supply 0...20 V Under this heading in "Radio", 1998, #5 a description of a simple block power supply on KR142 series microcircuits. Feature of the new version block is the probability of smoothly setting the threshold for limiting the output current from units of milliamps to the maximum value. The main difference of the modified power supply (Fig. 1) is contained in the introduction of the operational amplifier DA2 and the installation of a negative voltage stabilizer microcircuit -6 V instead of -1.25 V. While the output current is small and the voltage drop across the current-measuring resistor R2 is less than that installed by resistor R3, there are 6 op-amps at the output and at the input of the DA1 microcircuit (pin 2) the voltage values are approximately equal, the diode VD4 is closed and the op-amp does not participate in the operation of the device. If the voltage drop across resistor R2 becomes greater than across resistor R3, the voltage at the output of microcircuit DA2 will decrease, diode VD4 will open and the output voltage will decrease to the value corresponding to the set current limit. Horse racing circuit diagram The transition to current stabilization mode is indicated by turning on the HL1 LED. Since in short-circuit mode the output voltage of the op-amp should be less than -1.25 V by approximately 2.4 V (voltage drop across diode VD4 and LED HL1), the voltage of the negative power supply of the op-amp was selected equal to -6 V. This role is needed for all positions of switch SA2, so it was necessary to switch and rectifier input VD2, VD3. The KR1168EN6B microcircuit can be replaced with a similar one with index A, with MC79L06 with indices BP, CP and ACP, as well as with KR1162EN6...
Digital technology Digital scale/Frequency meter DS018 Device characteristics: Measured frequency range 1 kHz...35 MHz. Frequency reading resolution 100 Hz. Reading update rate constant, 5 times/sec. Input signal voltage not less than 0.5 V. eff.Device supply voltage: 7...24V.Consumption current no more than 100mA** Total current consumption of DS018 and DLED1_6 no more than 70mA.Measuring Features Blok DS018 Possibility of use in frequency meter mode. Separate version of the Measuring block DS018 and Indicator. Minimum number of connecting wires (GND; Data). Reading update rate 5 times/sec. Data transfer rate from Measuring Blok DS018 to the Indicator was chosen as minimal as possible, which made it possible to get rid of interference on the sensitive receiving path of the transceiver without any additional shielding. Separate power supply of the Measuring Blok DS018 and Indicator. The length of the communication line between the Measuring unit and the indicator is up to 5 meters (I). Digital hysteresis of the least significant digit minimizes its “jitter”. Possibility of parallel connection of an unlimited number of indicators to one DS018 Measuring Unit (duplication of readings). Operable in transceivers using local oscillator frequency doubling (*2). Supports up to 12 operating ranges. Short-term transition to frequency meter mode when pressing a button located on the Measuring Unit board. Possibility of repeated (at least 100,000 times) reprogramming by the User of the IF value or the “stand” frequency for each range separately as well as the sign (addition or subtraction ).Easy to understand and convenient for the User to change settings.Non-volatile EEPROM memory for storing User settings.Safety of User settings for more than 10 years without supply voltage.User-disabled EEPROM memory armor from accidental erasure during power failures.Possibility of electronic cal...
TelevisionEXPANSION OF THE FREQUENCY RANGE UHF STANDBONESUntil recently, many types of UHF set-top box selectors were produced, designed to receive television signals on any of the 21 UHF channels (from 21 to 41) and convert them into meter range signals (1st and 2 th channel). Absence block UHF in televisions of previous generations forced many to purchase UHF set-top boxes. In Vitebsk, a transmitter on channel 48 was recently turned on. To expand the received range to the 59th channel, I propose the simplest modification of the Uman selector set-top box and similar ones with a range of 21 ... 41 channels. The improvement consists of increasing the tuning voltage (UH) of the vari-caps to 26 V (instead of 18 V). To do this, you need to break the connection between stabilization resistors R2 and R3 and apply pin 3 of resistor R2 to point R1 (Fig. 1). You can do this by switching through a toggle switch (Fig. 2) - then the range of 21...41 channels is preserved. Puc.2After this, tune to the 48th channel (or another of this order) as usual. This modification is done in a similar way on other types of UHF selector set-top boxes, designed to receive 21...41 channels. Their schemes are practically unified. V. REZKOV, 210032, Vitebsk, Chkalova st., 30/1 - 58. ...
The power supply described below can be used for portable and small-sized radio devices (radios, radios, tape recorders, etc.). Technical data: Output voltage - 6 or 9 V Maximum load current - 250 mA The power supply has a parametric current stabilizer and a compensation voltage stabilizer. Therefore, it is not afraid of a short circuit at the output, and the output transistor of the stabilizer practically cannot fail. Scheme block power supply is shown in the figure. The parametric current stabilizer includes the R1C1 chain and the primary winding of the T1 transformer. The compensation voltage stabilizer is assembled on elements R2, VT1, VD2, VD3, VD4. The operation of the circuits has been repeatedly described in the literature and is not presented here. LED VD5 (red) with ballast resistor R3 serves to indicate operability block nutrition. Details: C1 - any small-sized paper with a rating of 0.25 µF x 680 V; C2, SZ - 1000 µF x 16 V; VD1 - KTs407A; VD2 - D18; VD3 - KS139A; VD4 - KS156A; VD5 - AL307A, B; VT1 - KT805AM; T1 - magnetic circuit Ш12 x 18, primary winding 2300 turns with PEV-0.1 wire, secondary winding - 155 turns with PEV-0.35 wire. The power supply fits into a plug housing from an imported adapter. O.G. Rashitov, Kiev...
I propose a simple switching power supply circuit. It differs from previously published diagrams in its simplicity, minimal number of parts and does not contain scarce elements. A correctly assembled unit does not require adjustment or configuration. The unit is also not afraid of short circuits and load breakage at the output. The disadvantages include low output power - 1 W at load and a high ripple factor at the output. Scheme block presented in the figure. As you can see from the diagram, this is a regular blocking generator. During forward motion, energy accumulates in the core of the transformer "And, during reverse motion, the output voltage is applied to the open diode VD3 and accumulates on capacitor C4 and then goes to the load. Unlike conventional circuits, the blocking generator is powered by a pulsating half-wave voltage. In view small capacitance C1, and also thanks to the current-limiting resistors R1 and R2, the voltage on the capacitor does not exceed 120 V in operating mode. Intercom electronics pu-02 In this case, it turned out to be possible to use a relatively low-voltage transistor in the unit. The purpose of the elements VD4, VD5 is to limit the reverse voltage on the collector junction of transistor VT1, at a safe level.In addition, the chain VD4, VD5 stabilizes the output voltage within 16 V without load, i.e. serves as a load for block in the absence of external load. Therefore, the presence of this chain is mandatory. The T1 transformer is made on the B-22 M2000NN armored core. Winding Ia contains 150 turns, winding Ib contains 120 turns. The windings are made with PELSHO wire 0 0.1 mm. Winding II contains 40 turns of PEL wire 0 0.27 mm, winding III contains 11 turns of PELSHO wire 0 0.1 mm. First, winding Ia is wound, followed by winding II. After this winding 16 and finally winding III. Instead of transistor VT1 could...
TelevisionHOW TO INCREASE THE SERVICE LIFE OF A CINESCOPE Assembling a circuit for delaying the switching on of a picture tube according to the article by A. Ilyin (RL 4-95), option for block MZZ, I found that this device needs some improvements. 1. Zener diode VD1 in the circuit is used as a key element that opens with voltage, and its operating current here is much less than 3 mA - the minimum permissible according to technical conditions. In this mode, the opening threshold of the KS 156 zener diode turned out to be only approximately 2 V (at a current of 30 μA). Therefore, to increase the delay time and more efficient use of capacitance C1, it is better to install a second zener diode VD1.1 in series with VD1. Also, to increase their operating current, it is advisable to reduce R3 to 30 kOhm. 2. With a capacitance of C1 of 220 μF, the device is ready to be turned on again no earlier than after 30 s, since the discharge occurs through R4 with high resistance. Do-it-yourself charger for a miner's flashlight To speed up this process, R4 should be bypassed with a diode VD2. When charging, it is closed by the voltage from the +12 V source, and after turning off the TV, it opens with potential from C1, and the discharge quickly occurs through the direct resistance of the diode. 3. Instead of C1 at 6.3 V, it is better to take a 25 V capacitor. Capacitors at a higher voltage are more stable, and most importantly, they “dry out” less over time. All of the above applies to the option for MC2, because they have the same delay interval generation unit. A. SKORLUPKIN, 410028, Saratov, Radishcheva St. 23 "b" - 2. (RL 3/98)...
Have you ever wanted to turn on the TV, stereo or other equipment when you are in the car or relaxing in nature? An inverter should solve this problem. It converts 12 V DC to 120 V AC. Depending on the power of the Q1 and Q2 transistors used, as well as how “big” transformer T1 is, the inverter can have an output power from 1 W to 1000 W.
Schematic diagram
List of elements
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Element |
Qty |
Description |
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Tantalum capacitors 68 µF, 25 V |
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Resistors 10 Ohm, 5 W |
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Resistors 180 Ohm, 1 W |
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Silicon diodes HEP 154 |
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npn transistors 2N3055 (see "Notes") |
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24 V transformer with a tap from the middle of the secondary winding (see "Notes") |
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Wires, housing, socket (for output voltage) |
Notes
