When choosing a power source to power LEDs, the right solution would be a PWM voltage regulator - for example, on the NE555 chip. The principle of operation of such a device is to pulse the supply of a given constant voltage to an LED with different duty cycles. So, for example, if a voltage pulse lasting only 0.1 second is applied to an LED per unit of time (for example, one second), then the brightness of the LED will be 10% of its power, and if a pulse lasting 0.9 seconds is applied - 90%. This process is shown in graph 1.
The PWM circuit of the LED brightness controller is shown in Figure 1. The circuit is assembled on the NE555 chip and is a pulse generator with an adjustable duty cycle. The duty cycle of the pulses of this device depends on the rate of charge and discharge of capacitor C1. The charge of capacitor C1 is carried out through the circuit R2, D1, R1, C1, and the discharge is carried out by C1, R1, D2, pin 7 of the microcircuit. Thus, by changing the resistance of resistor R1, we change the charging and discharging time of capacitor C1 - thereby adjusting the duty cycle of the pulses at the output of the microcircuit (pin 3). At pin 3 of the microcircuit, the logical value “0” is +0.25V, and the logical value “1” is +1.7V. Thus, a voltage of +0.25V will not open transistor T1 - and at the output of the device, during a given period of time, there will be no voltage, and a voltage of +1.7V will open transistor T1 completely. Transistor T1 is represented by a CMOS field-effect transistor IRFZ44N whose power reaches 150 W. However, if you use more powerful transistors as T1, you can achieve greater output power of the device. As diodes D1, D2, you can use diodes 1N4148 or any of the series diodes 1N4002 - 1N4007.
Fig.1. Circuit PWM LED brightness controller on NE555
This device is also widely used as a speed controller for DC motors. To do this, another diode is added to the circuit, installed at the output of the device (the cathode of the diode is connected to +Upit., the anode of the diode is connected to the drain of transistor T1. This diode protects the device from reverse voltage coming from the motor after turning off the power to the device.
A regulator circuit based on pulse width modulation, or simply , can be used to change the speed of a 12 volt DC motor. Regulating the shaft speed using PWM gives greater performance than simply varying the DC voltage supplied to the motor.
The motor is connected to field-effect transistor VT1, which is controlled by a PWM multivibrator based on the popular NE555 timer. Due to the application, the speed control scheme turned out to be quite simple.
As mentioned above, engine speed controller made using a simple pulse generator generated by an astable multivibrator with a frequency of 50 Hz made on the NE555 timer. The signals from the output of the multivibrator provide bias to the gate of the MOSFET transistor.
The duration of the positive pulse can be adjusted with variable resistor R2. The greater the width of the positive pulse entering the gate of the MOSFET transistor, the more power is supplied to the DC motor. And vice versa, the narrower its width, the less power is transmitted and, as a result, the reduction engine speed. This circuit can operate from a 12 volt power source.
Characteristics of transistor VT1 (BUZ11):
The switching regulator is designed to power low-voltage incandescent or halogen lamps. The figure shows the circuit diagram of the device, NE555 is used as an astable oscillator and produces pulses with variable duty cycle (0.1 to 0.99). The duty cycle is controlled by resistor R4. NE555 controls the operation of transistor VT1, the device can be used with lamps with power up to 60 W (12V), while the radiator for the transistor […]
A small-sized power supply is used instead of a KRONA battery and is placed in the battery compartment of the device. The power supply uses a voltage converter (15 kHz). The output voltage of the power supply is 9V at a load current of 50 mA. The diode rectifier VD1 is powered by the voltage limiter zener diode VD2. The rectified voltage supplied to the converter (VT1) is 15V. The voltage from the secondary winding of the transformer is rectified by a diode […]
This switching power supply can be used in stereo amplifiers. The output stage is made according to a single-cycle circuit with reverse connection of rectifiers. The pre-output converter is made according to a transformerless circuit using 3 transistors VT1-VT3. A negative pulse is removed from pin 13 of the IC, the duration of which is proportional to the feedback voltage supplied to pin 3 of the IC. A pulse of positive polarity removed from the collector VT1 opens VT2, […]
When the power is turned on, C1 is smoothly charged through R4, which serves to protect the diode bridge from overload at the moment of switching on. An oscillatory process occurs in the oscillatory circuit thanks to the dividers R2R6, R1R3, R5R7. Energy is removed from the oscillatory circuit by secondary windings IV and V. HF oscillations are rectified by diodes VD5VD6 and smoothed by capacitor C3. The stabilizing load is a zener diode VD7. Current […]
Since most digital microcircuits have a +5V power supply, when using a vacuum indicator, problems arise with its power supply. The fact is that almost all indicators of the IV or IVL type are designed for an anode voltage of 22-27V and an alternating voltage of 3-3.5V. Such indicators are absolutely inoperable with a 5V power supply. To ensure normal operation of the indicator from 5V, it is necessary to introduce […]
To power devices on the op-amp, a voltage of +/-10...15V is required, with a current consumption of no more than 10-20mA (2-3 op-amps), this UPS is designed for such devices. The mains voltage is suppressed to a level of 50V using a parametric stabilizer - C1 VD1 C2 VD2. This voltage powers a 2-cycle pulse generator on VT1 VT2, assembled according to a symmetrical multivibrator circuit. To the collector circuit […]
The uninterruptible power supply provides output power up to 220 W. In the circuit (see figure), the voltage of the lead-acid car battery GB1 is applied to the master oscillator on the DD1 chip with a frequency of 50 Hz, which swings powerful key transistors that alternately apply 12 V to the windings Ia and Ib of step-up transformer T2. From the secondary winding T2 voltage is 220 V with a frequency of 50 […]
The switching power supply (see figure) consists of mains voltage rectifiers, a master oscillator, a rectangular pulse shaper of adjustable width, a two-stage power amplifier, output rectifiers and an output voltage stabilization circuit. The master oscillator, made on microcircuit elements DD1.1, DD1.2 (K555LA3), produces rectangular pulses with a frequency of 150 kHz. An RS trigger is assembled on elements DD1.3, DD1.4, at the output of which the frequency of the output signals is […]
Presented to your attention is a circuit assembled on the basis of the NE 555 timer (domestic analogue of KR1006VI1).
Rice. 1 PWM voltage stabilizer circuit
The schematic diagram of the stabilizer is shown in Fig.1. Generator on DA1 ( NE 555), similar to that described in, works on the phase-pulse principle, because The pulse width remains unchanged and equal to hundreds of microseconds, and only the distance between the two pulses (phase) changes. Due to the low current consumption of the microcircuit (5...10 mA), I increased the resistance of R4 almost 5 times, which made its thermal regime easier. The key stage on VT2, VT1 is assembled according to the “common emitter - common collector” circuit, which minimized the voltage drop on VT1. The power amplifier uses only 2 transistors, because the high output current of the microcircuit (according to 200 mA) allows you to directly control powerful transistors without an emitter follower. Resistor R5 is necessary to exclude through current through the emitter-base transitions VT1 and collector-
Fig.2
emitter VT2, which for open transistors are connected as two diodes. Due to the relatively low speed of this circuit, it was necessary to lower the frequency of the generator (increasing the capacitance of C1). The input voltage should be the maximum possible, but not exceed 40...50 V. The resistance of resistor R8 can be calculated using the formula
So, if the input voltage is 40 V, and at the output it should vary within 0...25 V, then the resistance R8 is approximately 6 kOhm. The most significant disadvantage of switching stabilizers compared to linear ones is that due to the pulse mode of operation, a high ripple coefficient (“whistle”) is observed at the output, which is very difficult to eliminate. It is advisable to include another similar filter in series with filter L1-C3.
The most significant advantage of this circuit is its high efficiency, and with a load current of up to 200 mA, a radiator on VT1 is not needed. A drawing of the stabilizer printed circuit board is shown on Fig.2. The board is attached to the radiator using the VT1 transistor soldered to it, but it can be attached to the chassis separately from the transistor. The length of the connecting wires in this case should not exceed 10...15 cm. Resistor R7
Imported, variable; instead, you can use a trimmer or variable, which is located outside the board. The length of the wires in this case is not critical. Choke L1 is wound on a ring with an outer diameter of 10...15 mm with wire d=0.6...0.8 mm until filled, the choke of the additional filter is wound with the same wire on a coil from the transformer, the number of turns should be maximum. Transistor VT2 - any average power (KT602, KT817B...G).
Capacitor C1 is better than film (with low leakage). It is advisable to fill the L1 throttle with paraffin, because it whistles quite loudly.
A. KOLDUNOV
The 555 timer chip (domestic analogue of KR1006VI1) is so universal that it can be found in the most unexpected electronic components. This article discusses switching power supply circuits that use this microcircuit.
In a home laboratory, especially in the field, a low-power source of different constant voltages is needed, which can be powered from batteries or galvanic cells, lightweight and portable. Similar circuits of switching power supplies, which are commonly called DC/DC converters, can be created using a 555 timer. It so happens that we use the NE555 microcircuit in our designs, but any of its analogues can be used in the circuits under consideration.
It is assembled on a single NE555 chip (Fig. 1), which serves as a master generator of rectangular pulses. The generator is assembled according to the classical scheme. The generator output pulse repetition rate is 6.474…6.37 kHz. It varies depending on the supply voltage, which can be 3.6 V (3 batteries in a power cassette) and 4.8 V (with 4 batteries in a power cassette). In the switching power supply circuit, ENERGIZER AA batteries with a capacity of 2500 mAh were used.
Rectangular pulses from output 3 of MS 555 are fed through limiting resistor R5 to the base of transistor switch VT1, the load of which is inductor L1 with an inductance of 3 mH. When this transistor is abruptly closed, a large self-induction EMF is induced in inductor L1. The high-voltage pulses obtained in this way are supplied to two parallel rectifiers with voltage doubling, the outputs of which will have two opposite-polar voltages ±4.5...15 V.
These voltages can be adjusted by changing the duty cycle of the output pulses using potentiometer R1. The constant voltage from the R1 engine reaches pin 5 of the MC555 and changes the duty cycle, and therefore the output voltage of both rectifiers. The output voltages of this source will be ideally equal only when the duty cycle of the generator pulses is equal to 2 (the duration of the pulses is equal to the pause between them). With a different duty cycle of the pulses, the output voltages of the source at points A and B will differ slightly (up to 1...2 V). Such a small difference is ensured by the use of doubling rectifiers in the switching power supply circuit, the capacitors of which are charged by both positive and negative pulses. This disadvantage is compensated by the simplicity and low cost of the scheme.
In this switching power supply circuit, you can use chokes from electronic ballasts of unusable energy-efficient fluorescent lamps. When disassembling these lamps, be careful not to damage the spiral or U-shaped glass tubes, as they contain mercury. It is better to do this outdoors.
On some chokes, especially imported ones, the inductance value in mH is marked (2.8, 2.2, 3.0, 3.6, etc.).
Input and output voltages, current consumption and pulse repetition rates for the circuit in Fig. 1 are given in Table 1.
Figure 2 shows a switching power supply circuit with two NE555 timers. The first of these microcircuits (DD1) is connected according to a multivibrator circuit, the output of which appears short rectangular pulses taken from pin 3. The repetition rate of these pulses is changed using potentiometer R3.
These pulses are sent to the differentiating circuit C3R5 and the diode VD1 connected in parallel to resistor R5. Since the cathode of the diode is connected to the power bus, short positive bursts of differentiated pulses (edges) are shunted by the small forward resistance of the diode and have an insignificant value, and negative bursts (falls), falling on the locked diode VD1, freely pass to the input of the waiting multivibrator MS DD2 (leg 2 ) and launch it. Although VD1 is indicated in the diagram as D9I, in this position it is advisable to use a low-power Schottky diode, and, in extreme cases, you can use a silicon diode KD 522.
Resistor R6 and capacitor C6 determine the duration of the output pulse of the standby multivibrator (one-shot) DD2, which controls switch VT1.
As in the previous circuit of a switching power supply, the current through transistor VT1 is regulated by resistor R7, and the load is a choke made from the ballast of economical 3 mH fluorescent lamps.
Since the MS generation frequency is lower than in the first circuit, the voltage doubling rectifier capacitor C7 has a capacity of 10 μF, and to reduce the size, a ceramic SMD capacitor is used in this position, but other types of capacitors can be used: K73, KBGI, MBGCh, MBM or electrolytic at a suitable voltage.
Input and output voltages, current consumption and pulse repetition rates for the circuit in Fig. 2 are given in Table 2.
The switching power supply circuit shown in Fig. 3 is similar, but an operational amplifier (OA) type K140 UD12 or KR140 UD 1208 is used as the master oscillator of rectangular pulses. This op amp is very economical, can operate from a unipolar supply voltage from 3 to 30 V or from bipolar ±1.5... 15 V.
The generation frequency is adjusted with potentiometer R3. To increase broadband, pins 1,4,5 are combined and grounded to a common wire. Resistor R6, which regulates current control, is reduced to the minimum possible value of 100 kOhm. The current consumption of the op-amp is within 1.5…2 mA. Between the output of the op-amp and the differentiating circuit C3R10VD1, from which the one-shot DD1 is launched, a buffer amplifier is connected on a transistor VT1 of type BC237, which serves to increase the steepness of the front and fall of the output pulse MS DA1. 
The load of the VT2 switch uses inductor L1 from the same ballasts from energy-efficient lamps. This inductor is protected from overvoltage by the R13VD2 chain. Its inductance is 1.65 mH, but it is wound with a thicker wire, therefore, its active resistance is lower and its quality factor is higher. This allows you to get a voltage of approximately 24...25 V at the output of the rectifier with doubling VD3VD4.
It should also be noted that the switching power supply circuit in Fig. 3 can operate from a unipolar supply voltage of 3.3 V.
Input and output voltages, current consumption and pulse repetition rates for the circuit in Fig. 3 are given in Table 3.
