Improving one of the previously published triac regulators, author improved it performance, complemented by a node overload protection and confirmed their technical solution calculations.
When establishing a triac controller, assembled according to the description in [1], was discovered that enter it in the maximum power in the load fails. "Culprit" turned out to be a generator for the unijunction transistor KTA, outstanding in each half-cycle of mains voltage, and the pulse. In the result is a capacitor in the power supply circuit of the amplifier pulses do not have time to recharge for the next half-cycle and the pulse energy was not enough to open of the triac.
Diagram of the improved regulator shown in the figure. It is not only eliminated the above described disadvantage, but also provides protection device exceeding the permissible value of the current in the load circuit.
In contrast to the prior art, the pulse generator is complementary a pair of transistors (VT1 CTG, VT2 CTH). When growing as charging of the capacitor C3, the voltage at the emitter of the transistor VT1 exceeds the voltage at its base, the generator produces a single pulse. Both transistors avalanche opened, the capacitor C3 is discharged mainly through the plot the base-emitter of the transistor VT3. This transistor opens and the capacitor C5 discharges through the winding I of the pulse transformer T2. Momentum with winding II pulse transformer opens the triac VS2.
Transistors VT1 and VT2 remain open until the transition of the mains voltage through zero, more precisely, to reduce the voltage on the supply bus 4...6 V. After them closing the generator is ready to give another impetus. The date of issue of the pulse is determined by the duration of charging of the capacitor C3 until the voltage opening transistors and depends on the total resistance constant of the resistor R7 and variable R6.
Due to the fact that in each half-cycle, the generator produces only one the impulse discharge capacitor C5 always has the ability to charge via diode VD8 for almost a half period, except for a brief interval, when the instantaneous value of the mains voltage is close to zero. With the average current charging SAR.CP approximately 9 mA (it depends on the resistance of the resistors R1 and R2), the capacitor C5 will have time for a half cycle (10 MS) to charge for up to 22 In (limited Zener diodes VD2 and VD3), if its capacity is not more than
What can be the minimum capacitance of this capacitor? To triac VS2 (TS-50-6, [2]) opened, the voltage on the control electrode should Uy to exceed 4 In for at least tвкл - 12 ISS. Current control electrode iy with the high voltage - 200 mA.
The resistance of the circuit control electrode Ry can be estimated from Ohm's law:
Taking into account the transformation ratio of transformer T2 is given to him the primary winding voltage and resistance:
From the equation
where U0=22 To - source voltage on the capacitor C5, find
The capacitance of the capacitor C5 is chosen equal to 1 µf.
Device overload protection is performed on the SCR VS1 COG. Under the effect of sensor overload - current transformer T1 - SCR open, resulting in a lower voltage at the output of the diode bridge VD1 to approximately 4 V. This is less than the voltage stabilizing Zener diode XA (VD7). Therefore, the pulse generator transistors VT1 and VT2 stops working triac VS2 no longer opens. Actuation of protection shows glow led HL1.
Due to the capacitor C1 and the diode VD6, the current through SCR VS1 in moments of transition mains voltage through zero does not stop and the SCR remains open. To return the controller to fire protection in working condition, need for a few seconds (sufficient time to discharge the capacitor C1) to disable it from the network.
The voltage on the secondary winding of the transformer T1 is proportional to the current, the current in the primary winding, connected in series in the load circuit. On managing the electrode of SCR VS1 supplied voltage secondary winding, rectified by diodes VD4 and VD5. By means of trimmer resistor R4 regulate the threshold of protection. The capacitor C2 prevents it from triggering impulse noise.
The current transformer as sensor overload is convenient because even if the current significantly exceeding a threshold (e.g., when short circuit load), the voltage at its secondary remains safe for other elements of the device. This is due to a sharp the reduction ratio due to the saturation of the magnetic circuit.
Applied to the regulator, the transformer T1 is made of a transformer T-W-ZM subscription loudspeaker. Similar can be found in some telephone devices. Its section is W-shaped magnetic core SM=64·10-6 m2, the average length of the magnetic line lM = 72·10-3 m. the Experimentally determined the relative magnetic permeability μ=0,7·103 through the induction of no more than 1 Tesla. Saturation occurs when induction...1,8 1,6 TL.
Here is the calculation of the current transformer:
1. The field strength required to obtain induction b = 1 T,
2. The needed ampere-turns
3. The amplitude of the load current at maximum power P=2500 W and effective the value of the voltage U=220 V equal
4. The number of turns of the primary (current) winding
Take w1=5.
5. The inductance of the primary winding
6. The inductive reactance of the primary winding at the frequency f=50 Hz
7. The voltage drop in inductance of the primary winding
8. For reliable opening of SCR CW need to apply for it the gate electrode a voltage not less than 15 In [2]. That this should be the amplitude of the voltage on the secondary side of U2. The number of turns
Since the device incorporates a full-wave rectifier (diodes VD3, VD4), the secondary of the transformer must actually consist of twice number of turns - 1500 with a branch of the middle. Flowing through this winding current is very small, so the wire diameter is chosen based only on its mechanical strength and the possibility of placing the desired number of turns in the window of the magnetic circuit.
The primary winding is wound in a single layer on top of well-isolated secondary the wire at least 4...5 mm2. Wire this section is very inconvenient to winding, so it is better to use a harness from a large number of thin wires the total cross-section equal to the desired one. The wiring harness are connected in parallel.
The establishment of the regulator is reduced to the setting current tripping a trimming resistor R4 and to the selection of the resistor R7, which depends on the upper limit of the range of regulation power (usually 94...97%). The nominal value of R7 is chosen so that at maximum power there were "omissions" of half-cycles due to podrywania triac VS2.
To suppress generated by the radio controller should be used recommended in [1] filter.
Literature
Author: B. Lavrov, St. Petersburg