Triac regulator

This triac controller was built to test the functionality of the scheme. Before describing the connection, first a little theory, according to Amateur Radio – Practical Electronics: “Triac is a 5-layer bistable semiconductor switching component designed for alternating voltage switching. The current in the control electrode G makes it possible to determine the closing moment at both half-waves of alternating voltage. Triacs are very sensitive to overvoltage switching, i. nap. higher than their max. closing voltage (as a precaution, the Amat transil can be used. radio 11/93, s.25). K zopnutiu triakov (and thyristors) a short pulse is enough (microsecond units) according to A4 / 02, s.30.

To make the triac switch, the holding current must be exceeded for the switching time. This holding current is not exactly the same for both directions of conductivity and can happen, that one half of the triac switches irregularly. This leads to the formation of a one-way component, which supersaturates the magnetic circuit, which also increases the AC component of the current. These phenomena work against each other and it is not easy to find the cause. Therefore, I do not recommend oversizing the triacs! According to ARPE 1/00 str.11 (RC triac member R = 39J, C=10n TC342).

230V engine speed regulator

Triac switching circuit (for engines) should switch using a capacitor, which determines at what speed the opening angle of the triac reaches the set size. The capacitor thus enables the function of the so-called. slow (delayed) ramp-up or soft start (Soft-Start). Therefore, if a universal motor is connected to such a speed controller with Tc, cannot at min. rotation angle of the triac, because it is braked by friction. The motor will only spin at the opening angle Tc at which the moss is. friction in the engine overcome. This useless time (Deadtime) can be removed by, that a resistor of suitable resistance is connected in series between the terminals of the control circuit and the control capacitor (count on it on PCB!). Voltage drop across this resistor, which is caused by the current flow, shifts the initial opening angle Tc from zero closer towards the mean value and thus obtains a slow rise function without delay. According to ARPE Elektus 2000 str.25.

A serial RC element is connected in parallel to the triac to protect Tc from voltage surges from motors and under. (100n/1kV, 180/2W) and a pi-element with two 100n / 1kV capacitors and a choke is inserted before the whole connection for interference suppression. According to AR-A 2/02, str. 4.

It is necessary to eliminate the interference, to keep the triac open for periods. According to ARPE 2/02, str. 28. At inductive load, or a longer supply cable, it is necessary to use an RC element that dampens voltage surges, which could cause a breakdown of Tc (180/2W, 100n/1kV paral. and Tc). can be removed, if necessary, by placing in series between the development, str. 29. (RC obv. pre odrušenie Tc APE2/03 26 51J, 10n/630V)

Triac regulator connection

So much theory from Amateur Radio magazine. The connection itself: KT207/400 was used and I don't ER900 (28-36V). Voltage divider, which forms a fixed resistor 10k, 47k potentiometer and 68k resistor charges capacitor, whose capacity has been reduced from the original 100nF to 3,3 nF due to faster switching of Dc and Tc. When the voltage on the capacitor exceeds the switching level, the diode opens quickly and the pulse switches on the triac. resistor 100 ohm provides protection for semiconductor components. The test load consisted of a 15W/230V light bulb, the voltage divider consists of three resistors 10k-47k-68k and therefore the total current to the divider is small, which saves the potentiometer path.

Triac regulator test

A failure occurred during verification. After the light came on and the light was adjusted, something quietly burst and the light went out. At first I thought, that a triac or diac has left. Well, it was a protective resistor 100 ohm/0,25W. That's why I replaced it with a more powerful one and then a bigger one, with value 240 ohm/0,5W (Russian, as otherwise….).

Furthermore, the controller could be supplemented with a switch for shutdown, switch for switching “fully” – parallel across the triac, so as not to overheat unnecessarily and fuse, in case half of the triac burns into the inductive load (engine) would be a unidirectional voltage (there is a risk of burning the winding!). By being the load at the terminal marked as phase, the electrode A2 (is connected to a metal housing) will be connected to the ground, the triac will not have to be isolated from the heatsink (device skeleton). Low current, which flows through a voltage divider and a capacitor charging current “forms / preheats” load and thus eliminates the impulse when switching on, for example, with a cold filament of strong light bulbs.

After checking the functionality, I started the second phase of the test. Simple triac regulators are not suitable for inductive loads, so I tested the regulation on the motor from the old ETA vacuum cleaner 411 500W. KT728 / 400 was used as a triac. Somewhere in front of the potentiometer path, the motor started and the regulation was good for a relatively simple regulator. Therefore, a 33k potentiometer will probably be more suitable.

Warning

It will also be appropriate to connect the RC suppressor to the triac. But I didn't involve him. Finally, I want to alert everyone, who engages they will want to try, that working with life-threatening tension and therefore caution is never enough. Address any questions to ss@stonline.sk