Three-channel power regulator with PWM modulation. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Protection of equipment from emergency operation of the network, uninterruptible power supplies
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Existing thyristor power controllers operate on the principle of cutting off a part of a sinusoid, and can only work when powered by an alternating voltage; moreover, it must be tied to the moment the voltage passes through zero. And if the network has significant interference, then the stable operation of this regulator is not possible at all. Sometimes a load frequency of more than 50...100 Hz is needed.
The proposed power regulator operates on the principle of PWM modulation of DC voltage (see figure).
(click to enlarge)
The output current in the load depends only on the duty cycle of the pulses, the accuracy of which mainly depends on the stability of the master oscillator and the linearity of the sawtooth voltage generator. The master oscillator is assembled on a chip D1.1, D1.2, resistors R1, R2 and capacitors C1, C2. The frequency of the generator depends on the rating and stability of discrete parts. In this case, at the output we have a meander with a repetition rate of 66 kHz. If more stability is needed, then a higher frequency oscillator can be used, followed by division using counters. On the chip D1.3, resistor R3 and capacitor C3, a simple sawtooth voltage driver circuit is made. PWM modulators are assembled on comparators D3, D1.4 and R4 (first channel), D4, D1.5 and R11 (second channel), D5, D1.6 and R12 (third channel).
Chips D2.1, D6, D7.1, D7.2 serve as switches for the upper and lower keys of channels 1-3. The three-key driver D10 is used to control the upper VT1-VT3 and lower VT4-VT6 transistors. Resistors R20-R24 and capacitor C19 have a protection circuit against excess power consumption by the entire load. When overloaded, the HL4 LED lights up. Potentiometers R6, R8, R10 serve as load power regulators. The driver chip is powered through a 15-volt D9 voltage regulator, and the entire digital part is powered from the D8 chip.
Details. As a transformer T1, you can use any one with a power of 2 ... 5 W and a secondary winding voltage of 18 ... 25 V. To control more power, transistors VT1-VT6 must be replaced with IGBT transistors of the IRGBC20KD2-S, IRGBC30KD2S type and installed on a radiator, as well as increase the capacities of C6, C7 and use more powerful ones instead of VD1-VD4. A piece of constantan wire with a diameter of 20 mm was used as a current shunt R1. Resistor R23 type SP5-2. Resistors R6, R8, R10 type SPZ-4am. All other resistors are of the type MYAT 0,125. Permanent low-voltage ceramic capacitors, except for C10, C13, C25 (they are designed for 50 V). Capacitors C8, C9 for a voltage of 1 kV, they must be located in close proximity to the transistors. Electrolytic capacitors type K50-35.
The adjustment is reduced to the selection of the resistance of the resistor R3 according to the highest linearity of the sawtooth voltage at input 3 (D3). Resistor R23 must set the threshold at which the protection will work.
This three-channel regulator can be used as an output node of a color and music installation; for this, voltage from band-pass filters must be applied to the inputs of 4 comparators. It is also necessary, for the purpose of electrical safety, to decouple the ULF and the device using a transformer or six optocouplers connected between outputs D6, D7 and inputs 2-7 (D10).
You can also experiment and turn on fluorescent lamps instead of incandescent lamps through chokes [1]. Perhaps the brightness of the glow to some extent will depend on the duration of the PWM pulses. This device can be used as a three-channel digital amplifier operating in class D [2].
References:
- Tarazov A. High-frequency power supply for a fluorescent lamp//Radio. - 2003. - No. 5. - S. 42.
- Abramov S. Digital low-frequency stereo amplifier//Radiator. - 2004. -№11. - S. 10.
Author: S.M. Abramov
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