SU426322A1 - CONTACT CURRENT DC KEY - Google Patents

Description

one

The invention relates to the field of automation and measurement technology.

Contactless DC switches are known, which contain a power transistor, the emitter of which is connected via a load to the common bus, and the collector is connected to the power bus through the transformer primary winding, and a diode and one of the secondary windings of the transformer are connected between the base and the emitter of the power transistor, and in series with another transformer secondary winding, connected by one of the leads to the base of the power transistor, a diode and a controlled key element, made, for example, on a transistor, are included zistor However, such devices cannot be controlled by short pulses.

In order to reduce the control power and increase the reliability of the proposed DC contactless switch, the emitter of the power transistor is connected through a series-connected capacitor, resistor and diode in addition to a common bus, and the junction of the diode and resistor is connected to a diode connected in series with a key element.

The drawing shows the scheme of the proposed contactless dc switch.

It contains a power transistor 1, the collector of which through the primary winding 2 of transformer 3 is connected to the power supply bus 4. A load filter 9 is connected between the emitter of the power transistor 1 and the bus 5 through the LC filter formed by the choke 6, the capacitor 7 and the discharge diode 8. A resistor 10, a diode 11 and a circuit comprising a series-connected winding are connected in parallel to the base and emitter of the power transistor 1 12 positive feedback and

diode 13. A capacitor 14, a resistor 15 and a diode 16 are connected in series between the emitter of the transistor 1 and a common length 5, and a diode 17 connected in series between the connection point of the latter and the base of the transistor 1, controlled by a key element 18 as shown in the drawing, a thyristor, a model of a thyristor, consisting of transistors, etc.) and a third winding 19 of the transformer.

Parallel to the capacitor 7 LC filter

included a chain of connected successively to the fourth winding 20 of the transformer

3 and diode 21.

Contactless key works as follows

in a way.

When a pulse arrives, turn on, for example, on the base of the power transistor 1, the last one is turned off by the pulse current. The action of the positive feedback circuit

transistor 1 after the end of the pulse

maintained in a state of saturation, with the base current proportional to the collector, and the proportionality coefficient is equal to the ratio of the numbers of windings 2 and 12. Through the open power transistor, energy is transferred from the power source to the load, and, in addition, the capacitor 14 is charged. yes flows through resistor 15 and diode 16.

When the pulse is turned off, which unlocks the controlled key element 18, the power supply pair is transferred to the sequentially and oppositely connected windings 19 and 2 via diodes 16 and 17, controlled by the key element 18 and the base-collector junction of the transistor 1. The number of turns of the winding 19 more than the number of turns of the primary winding 2 is selected. Therefore, after unlocking the key element 18, the polarity of the voltages on the windings of the transformer is reversed, which causes the diode 13 to be locked in series with the winding 12 ATN communication. From this point on, the positive base current is replaced by a negative one, with the magnitude of the latter being proportional to the collector current of the power transistor, and the proportionality factor is the ratio of the numbers of turns of the windings 2 and 19.

By the action of the negative base current, the power transistor 1 is brought out of saturation mode, and the process of reducing the collector current of this transistor begins. As a result, the potential at the emitter of transistor 1 increases, and with it the current through diode 16 first decreases and then the diode closes.

However, the flow of negative current into the base of transistor 1, necessary to maintain the process of its locking, does not stop. This current is provided by the discharge of the capacitor 14 through a series-connected diode 17, an open controlled key element 18 and a winding 19. The capacitance of the capacitor 14 is chosen so that this current flows through the capacitor, discharging it for a time slightly longer than the duration of the fallout of the power collector current transistor 1.

Thus, the negative current to the base of the power transistor 1, required for its locking, is automatically set for a time that is only slightly longer than the locking time of the transistor, determined by its inertia.

Diodes 16 and 17 can be shunted by a single diode. This somewhat reduces the energy loss when locking the power transistor.

The locked state of the transistor 1 after the end of the discharge of the capacitor 14 is maintained either by the presence of a sufficiently low-resistance resistor 10 in parallel to the emitter-base transition of this 5 transistor and simultaneously by the presence of a diode 13 in series with a winding threshold unlocked by voltage, or using an offset chain (in the drawing

0 not shown), locking the emitter junction of the power transistor 1.

During the current flow through the primary winding 2 in the transformer 3, the magnetic field of the magnetic field accumulates. After

5, lock the transistor this energy dissipates. In this case, "reverse voltages on the windings 2, 12 and 19 are blocked, respectively, by a locked transistor 1, a diode 13 and a diode 17. A diode 21 connected in series

0 with winding 20, is open, and current flows through it during the process of dissipating the energy of the magnetic field accumulated in transformer 3. At the same time, energy is transferred to the capacitor 7 of the LC filter in the transformer 3.

The increase in reliability in the proposed device is due to the fact that due to the proportionality between the collector current of the power transistor and the negative base current, which ensures its locking, the latter can be enforced at any value of the collector current. This simplifies the protection of the transistor against overcurrent.

Subject invention

A contactless dc switch containing a power transistor, the emitter of which is connected to the common bus through a load, and the collector is connected to the power bus through the transformer primary winding, and a diode and one of the secondary windings of the transformer are connected between the base and the emitter of the power transistor with the other secondary winding of the transformer connected by one of the conclusions with the base of the power transistor included

0 a diode and a controlled key element made, for example, on a transistor, characterized in that, in order to reduce the control power and increase reliability, the emitter of the power transistor is connected through a series-connected capacitor, resistor and diode in addition to a common bus, A diode and a resistor are connected to a diode connected in series with a key element.