Relay polarity switching circuit. Electronic polarity switch - Simple designs - Circuits for beginners

The circuit is an automatic polarity switch when you press a button.

Where might this be needed? Yes everywhere. Well, for example, in some toys. The car reached the wall, pressed a button - the car went back :) In fact, there are a lot of applications. Meanwhile, the device is extremely simple. Consists of only two microcircuits and several hanging elements.

Let's start from the beginning. That is, from a button.

As you, I hope, know, all switches, buttons, relays and other elements of mechanical switching have a very unpleasant property: “bouncing” of contacts. It is expressed in the fact that when a pair of contacts is closed, the current does not immediately begin to flow calmly through them. At first it “rattles” for some time - it makes damped oscillations. When the contacts are opened, the same problem occurs.

Often no one notices or takes into account the chatter, since for most circuits it does not pose a serious problem. But for our scheme it is - real problem. Because when the button is pressed once, the circuit will “think” that the button was pressed several times, which, of course, will lead to glitches. This means we need to fight him.

To combat bounce, our device has a clever circuit consisting of two inverters of the K561LN2 microcircuit, a capacitor and two resistors. We will not delve into the details of his work. Let me just say that this circuit is a Schmidt trigger with a time delay on and off. In short, after this scheme we get beautiful square pulses without any rattling.

These beautiful pulses are sent to the clock input of the trigger DD2 (561TM2). On each edge (change from 0 to 1), the trigger slams the state at input D. The signal to input D is supplied from the inverted output of the same trigger.

Then everything is very tricky. Let’s assume that the inverse output is 1. At the next front, it slams into the trigger, therefore, “1” appears at the direct output of the trigger, and “0” at the inverse output. This means that at the next front, a zero will slam into the trigger! In this case, “0” will appear at the direct output, “1” will appear at the inverse output again, and the process will begin again.

Thus, each edge will change the state of the flip-flop to the opposite.

In principle, we already have a polarity change at the trigger outputs each time the button is pressed. And if the load is low-power, you can stop there and hang it directly on the outputs of the microcircuit. However, it is better not to overload the microcircuit with current, but to install the most ordinary transistor amplifiers at its outputs. More precisely - drivers.

A driver is a buffer amplifier that amplifies the digital signal by current.

In principle, this is what we need. We will install one driver for each trigger output. Each driver consists of two transistors of different conductivity. When a positive voltage is supplied to the driver input, the NPN transistor is open, when negative, the PNP is open. I installed transistors KT502 and KT503 (PNP and NPN, respectively) in our circuit. These transistors can easily withstand currents up to 100 mA. What? Do you need more? OK! You can install more powerful transistors.

Powerful electronic MOSFET switches are a staple in consumer and specialty electronics and can be useful for controlling large loads. DC, without the use of high-current switches, whose contacts burn out and wear out over time. As is known, MOSFET field-effect transistors are capable of operating with very high voltages and currents. Which is highly in demand for connecting loads in different power circuits.

Electronic switch circuit

This circuit allows easy switching of low voltage pulses (5V) to drive large DC loads. The power of the MOSFET transistor indicated in the circuit is suitable to withstand voltages and currents up to 100 V, 75 A (for NTP6411). This electronic switch can be used instead of relays in your vehicle's modules.

A regular switch or pulse input can be used to activate the transistor. You can select the input method by installing a jumper on the appropriate side. The pulse input will probably be most useful. The circuit was designed for use with 24V, but it can be adapted to work with other voltages (tests were fine at 12V). The switch must also work with other N-channel MOSFETs. A protection diode D1 is included to prevent voltage surges from inductive loads. LEDs provide a visual indication of the transistor status. Screw terminals allow the device to be connected to different modules.

After assembly, the switch was tested within 24 hours together with solenoid valve(24V/0.5A) and the transistor was cool to the touch even without the heatsink. In general, this circuit can be recommended for the widest range of applications - both in LED lighting and in auto electronics, to replace conventional electromagnetic relays.

The utility model “DC power supply polarity switch” relates to the field of electronic non-contact switching and can be used in the production of electroplating, in DC electric drives, in thermal electrical devices ah heating-cooling.

The purpose of the utility model is to simplify the control circuit and protection against through currents power keys with optical isolation, combined into a bridge circuit consisting of two parallel-connected pairs connected in series field effect transistors, as well as reduction in size due to reduced heat losses.

To achieve the technical result, field-effect transistors with low drain-source resistance in the open state are used as power switches, and each of the parallel-connected pairs is formed by two back-to-back field-effect transistors with n-type and p-type channels, drains of transistors with the same type of channels are connected to each other and to the power supply connection terminals, the sources of transistors with different types of channels are connected to each other and to the load connection terminals, and input circuits The decoupling optocouplers are connected back-to-back to each other and to the switch control terminals through diodes and limiting resistors.

The utility model relates to the field of electronic contactless switching and can be used, for example, in DC electric drives, in the production of electroplating, in thermoelectric heating-cooling devices, that is, in cases where for the normal functioning of electrical devices or technological processes It is necessary to switch the polarity of the supply voltage.

A reversing switch is known, containing a bridge circuit on four power transistors of different conductivity and a circuit for preventing through currents, containing four additional transistors, two diodes, four resistors and a group of logical elements “and” (Patent RU 2140128, C1, class N03K 017/66, 2001 G.). However, this switch only works effectively on an inductive load, which does not allow it to be used, for example, in thermoelectric devices.

The solid-state relay “Power half-bridge module with optical isolation 5P64.GD”, produced by Proton-Impulse CJSC, Orel, was adopted as a prototype (a description of the module is attached in the “Other Documents” section). This module contains one pair of two IGBT transistors connected in series, the gates of which are connected to a control and protection circuit connected through optocouplers to an input logic circuit connected to the output circuits of the microprocessor. To act as a source polarity switch DC voltage it is necessary to use two such modules by parallel connection of the same terminals of the switched source.

The disadvantages of the prototype are the complexity of the power switch control circuits and their protection from through flows, as well as large losses in dissipated thermal power, which results in the need to use rather bulky heat sinks.

The purpose of the utility model is to simplify the control circuit and protect power transistors from through currents and reduce dimensions by reducing the thermal power removed from the transistors.

The technical result is achieved by the fact that, combined in a bridge circuit, two parallel-connected pairs of two series-connected field-effect transistors used as power switches, the gates of which are connected through optocouplers to control circuits connected to the output circuits of the control microprocessor, according to the utility model, differ in that field-effect transistors with low drain-source resistance in the open state are used as power switches, and each of the parallel-connected pairs is formed by two back-to-back transistors connected in series with n-type and p-type channels, the drains of field-effect transistors with the same type of channels are connected in each pair with each other and with the power supply connection terminals, the sources of field-effect transistors with different types of channels in each pair are connected to each other and with the load connection terminals, and the input circuits of the decoupling optocouplers through diodes and limiting resistors are connected in back-to-back parallel with each other and with the control terminals switch.

Figure 1 shows the principle electrical diagram switch, and figure 2 is a photograph of a prototype utility model.

The switch contains two parallel-connected pairs connected to terminals 1 of the power supply, each of which consists of two back-to-back MOS transistors with induced n-type and p-type channels.

One pair is formed by transistor 2 with an n-type channel and transistor 3 with a p-type channel, the other pair is formed by transistor 4 with an n-type channel and transistor 5 with a p-type channel. The drains of field-effect transistors 2 and 4 with the same type of channels are connected to each other and connected to the negative terminal of the power supply, respectively, the drains of transistors 3 and 5 are connected to each other and connected to the positive terminal of the power source. The sources of field-effect transistors 2, 3 and, accordingly, transistors 4, 5 are connected to each other and the load connection terminals 6, and the gates of these transistors are connected to the output circuits of optocouplers 7, 8, 9, 10, the input circuits of which are through limiting resistors 11 and diodes 12 connected back-to-back with each other and the switch control terminals 13.

The utility model works as follows.

In the initial state, when the control buses from terminals 13 from the control microprocessor are not supplied with voltage to turn on the LEDs of optocouplers 7, 8, 9, 10, power transistors 2, 3, 4, 5 are closed and, therefore, the load connected to terminals 6 is disconnected from power supply connected to terminals 1.

When a positive control voltage is applied to one of the buses of terminals 13, for example, to the top bus in Fig. 1, optocouplers 7 and 10 are activated and transistors 2 and 5 are opened, thereby connecting the load to the source; in this case, the positive terminal 1 of the power source is connected to the right (according to Fig. 1) terminal 6 of the load, and accordingly, the negative terminal 1 of the power source will be connected to the left terminal 6 of the load according to the diagram. When the control voltage is applied to the lower bus of terminals 13, optocouplers 8 and 9 will operate in the same way, transistors 3 and 4 will open, as a result of which the polarity of the power source to terminals 6 of the load is reversed.

Thanks to the back-to-back parallel connection of the input circuits of optocouplers 7, 8, 9, 10 through diodes 12 and resistors 11 with control buses, if the control microprocessor fails, when positive signals may appear on both control buses, the input currents of all optocouplers become equal to zero, which leads to disconnecting the load from the power source. The appearance on the “zero” control bus of a pulsed noise of positive polarity with an amplitude equal to or exceeding the amplitude of the control signals, or the appearance on a working control bus of a pulsed noise of negative polarity with the corresponding amplitude, also leads to a short-term (for the duration of the noise pulse) disconnection of the load from the source nutrition. In this case, resistors 11 limit the input current of the LEDs of optocouplers 7, 8, 9, 10 from positive impulses interference with an amplitude exceeding the control voltage, and diodes 12 provide protection for these LEDs in the presence of pulsed interference of negative polarity with an amplitude exceeding the permissible values ​​of the reverse voltages of these LEDs. Similarly, a bridge circuit of series-connected transistors 2, 3 and 4, 5 with different types of channels used in the utility model provides effective protection against through currents when the gates of these transistors are exposed to pulse noise induced on the power supply circuit. If all transistors 2, 3, 4, 5 are closed (the load is disconnected from the power source), pulsed noise of positive polarity can cause the simultaneous opening of transistors 2 and 4 and at the same time a simultaneous increase in the closing voltage of closed transistors 3 and 5, while the load remains disconnected from power supply. Similarly, when exposed to pulse noise of negative polarity, transistors 3 and 5 open and transistors 2 and 4 remain closed. If the load is connected to a power source, i.e. transistors 3 and 4, or 2 and 5 are open, then a pulsed noise of any polarity can only cause the corresponding open transistor to close, which will lead to a short-term load disconnection for the duration of the noise pulse, which does not lead to deterioration in the functioning of inertial processes or devices mentioned in the field of use this utility model.

The use of field-effect transistors with ultra-low drain-source resistance in the open state, made with a HEXFET crystal structure and called MOSFET transistors, as power switches makes it possible to reduce energy losses and eliminate the use of bulky heat sinks in the utility model (description “New MOSFET transistors of the IRFP4 family " is attached in the section "Other documents"). For example, when using NP100 transistors (transistors 3, 5) and IRF1404 transistors (transistors 2, 4), having an on-state resistance of 0.004 Ohms at a load current of 20 A, the voltage drop across one transistor will be 0.004 × 20 = 0.08 V, and the heat generation power will not exceed 0.08V×20A=1.6 W, while the permissible thermal power when operating these transistors without radiators is 2 W. For comparison, we note that the thermal power generated by the prototype when switching a direct current of 20 A will be (see attached technical characteristics) 3.2V×20A=64 W. In this case, the dimensions of the two prototype half-bridges combined into a bridge circuit will be 150×93×42 mm, while the dimensions of the prototype utility model shown in Fig. 2 are 90×60×18 (mm).

As can be seen from Fig. 2, the height of the utility model is determined by the height of terminal blocks 1 and 6. The power transistors of the utility model are mounted on heat-sinking sections printed circuit board, which allows switching currents up to 40 A with the permissible operating temperature transistors. When installing radiators in these areas that do not increase the height of the utility model, the latter provides switching currents of up to 100 A.

Thus, the advantages of the claimed utility model compared to the prototype are a simpler and therefore more reliable control circuit and protection of power transistors from through currents, lower heat losses, and, as a consequence, a more compact design.

A polarity switch of a DC power source containing two parallel-connected pairs of two series-connected transistors used as power switches, combined in a bridge circuit, the gates of which are connected through optocouplers to control circuits connected to the output circuits of the control microprocessor, characterized in that as power switches switches, field-effect transistors with low drain-source resistance in the open state are used, and each of the parallel-connected pairs is formed by two back-to-back transistors connected in series with n-type and p-type channels, the drains of field-effect transistors with the same type of channels in each pair are connected to each other and with the power supply connection terminals, the sources of field-effect transistors with different types of channels in each pair are connected to each other and to the load connection terminals, and the input circuits of the decoupling optocouplers through diodes and limiting resistors are connected back-to-back to each other and to the switch control terminals.

The circuit is an automatic polarity switch when you press a button.

Where might this be needed? Yes everywhere. Well, for example, in some toys. The car reached the wall, pressed a button - the car went back :) In fact, there are a lot of applications. Meanwhile, the device is extremely simple. Consists of only two microcircuits and several hanging elements.

Let's start from the beginning. That is, from a button.

As you, I hope, know, all switches, buttons, relays and other elements of mechanical switching have a very unpleasant property: “bouncing” of contacts. It is expressed in the fact that when a pair of contacts is closed, the current does not immediately begin to flow calmly through them. At first it “rattles” for some time - it makes damped oscillations. When the contacts are opened, the same problem occurs.

Often no one notices or takes into account the chatter, since for most circuits it does not pose a serious problem. But for our scheme this is a real problem. Because when the button is pressed once, the circuit will “think” that the button was pressed several times, which, of course, will lead to glitches. This means we need to fight him.

To combat bounce, our device has a clever circuit consisting of two inverters of the K561LN2 microcircuit, a capacitor and two resistors. We will not delve into the details of his work. Let me just say that this circuit is a Schmidt trigger with a time delay on and off. In short, after this circuit we get beautiful rectangular pulses without any chatter.

These beautiful pulses are sent to the clock input of the trigger DD2 (561TM2). On each edge (change from 0 to 1), the trigger slams the state at input D. The signal to input D is supplied from the inverted output of the same trigger.

Then everything is very tricky. Let’s assume that the inverse output is 1. At the next front, it slams into the trigger, therefore, “1” appears at the direct output of the trigger, and “0” at the inverse output. This means that at the next front, a zero will slam into the trigger! In this case, “0” will appear at the direct output, “1” will appear at the inverse output again, and the process will begin again.

Thus, each edge will change the state of the flip-flop to the opposite.

In principle, we already have a polarity change at the trigger outputs each time the button is pressed. And if the load is low-power, you can stop there and hang it directly on the outputs of the microcircuit. However, it is better not to overload the microcircuit with current, but to install the most ordinary transistor amplifiers at its outputs. More precisely - drivers.

A driver is a buffer amplifier that amplifies the digital signal by current.

In principle, this is what we need. We will install one driver for each trigger output. Each driver consists of two transistors of different conductivity. When a positive voltage is supplied to the driver input, the NPN transistor is open, when negative, the PNP is open. I installed transistors KT502 and KT503 (PNP and NPN, respectively) in our circuit. These transistors can easily withstand currents up to 100 mA. What? Do you need more? OK! You can install more powerful transistors.