How to match the user's drive circuit with the input characteristics of the solid state relay

Generally speaking, the input control voltage of the solid state relay is 3.2-32V. The control current is 5-30mA.Usually the SSR input circuit of 1-2 is not a constant current source circuit, and the input control voltage is 4-16V. The control current is 5-20mA, and the SSR input circuit with the larger rated current is connected to the constant current source circuit. The input control voltage is from 3.2 to 32V. In a three-phase circuit, if the user connects the three SSR inputs in series, then he wants to provide a control voltage greater than 12V. If the three SSR inputs are used in parallel, the drive current must be 50mA. For the use of a single SSR, the driving current should not be designed to be at least greater than 6mA in the critical state of 4-5mA.

Installation method:

Horizontal W-type, vertical L-type, small size, suitable for direct welding and installation of printed boards. The vertical L2 type is suitable for both soldering and installation of circuit boards and plugging and installation on circuit boards. When selecting the solid-state relay used in the printed circuit board with small current specifications, because the lead terminal is made of high thermal conductivity material, the soldering should be carried out under the condition that the temperature is less than 250 °C and the time is less than 10S.

Type K and F, suitable for radiator and instrument base plate mounting. When installing high-power SSRs (K-type and F-type packages), it should be noted that the contact surface of the radiator should be flat and coated with composite thermal grease (Meibo T-50). The greater the installation torque, the smaller the contact thermal resistance. The high-current lead-out wire needs to be equipped with a cold-pressed solder lug to reduce the contact resistance of the lead-out wire.

How it works:

Input loop

Solid state relays can be divided into resistive type, constant current source and AC input control type according to the input control mode. Currently, the main type of resistor input for 5VTTL level is available. When other control voltages are used, a current-limiting resistor can be selected accordingly. The SSR input is a current-type device, and when the optocoupler thyristor at the input end is fully turned on (on the order of microseconds), the power thyristor is turned on. When the excitation is insufficient or the ramp-wave trigger voltage is used, it is possible to cause the power thyristor to be at the critical conduction edge and cause damage caused by the main load current flowing through the trigger loop. When the input voltage is too high or the input current is too large to exceed the rated parameters specified in the input, it can be considered to connect the voltage divider resistor in series at the input terminal or connect the shunt resistor at the input port in parallel, so that the input signal does not exceed its rated parameter value.

For example, the basic performance test circuit, the input is an adjustable voltage source, the test load is a 100W bulb, and the input trigger signal should be a step logic level, and the strong trigger mode is used. The standard current of the device provided by foreign manufacturers is 10mA, considering the full temperature operating range (-40-+70°C), stable luminous efficiency and anti-interference ability, the recommended DC trigger working current is between 12-25mA.

The SSR inputs can be driven in parallel or series. When used in series, one SSR is considered to be 4V, and 12V can drive three SSRs. In specific use, the control signal and load power supply are required to be stable, and the fluctuation should not be greater than 10%, otherwise voltage stabilization measures should be taken.

interference

When installing and using, it should be kept away from electromagnetic interference and radio frequency interference sources to prevent the relay from malfunctioning out of control. SSR products are also a source of interference, and when turned on, they can generate radiated or RF interference from the power line through the load, and the degree of interference varies with the size of the load. Incandescent resistive loads produce less interference, and the zero-voltage type conducts near the zero-crossing zone (i.e., zero voltage) of the AC power supply, so there is less interference. The way to reduce this is to connect the inductor coils in series at the load. In addition, cross-interference should be avoided between the signal line and the power line.

Problems

When the solid state relay is open and there is voltage at the load end, there will be a certain leakage current at the output end, and care should be taken to prevent electric shock when using or designing. When the solid-state relay fails to be replaced, the original model or the product with the same technical parameters should be selected as far as possible to match the original application line and ensure the reliable operation of the system.

superheating

When the SSR is turned on, the component will be subjected to the dissipated power of P = V (tube voltage drop) × I (load), where the V rms and I rms values are the saturation voltage drop and the RMS of the operating current, respectively. The load capacity of the solid-state relay is greatly affected by the ambient temperature and its own temperature rise, according to the actual working environment conditions, strictly refer to the allowable shell temperature rise (75 °C) when the rated working current, reasonably select the size of the radiator or reduce the current use, in the process of installation and use, it should be ensured that it has good heat dissipation conditions, otherwise it will be out of control due to overheating, and even cause product damage.

Generally speaking, below 10A, the instrument base plate with good heat dissipation conditions can be used, the rated working current of more than 10A products should be equipped with radiators, below 30A, natural air cooling, when the continuous load current is greater than 30A, the instrument fan should be used for forced air cooling, and the products above 100A should be equipped with radiators and fans for strong cooling. During installation, attention should be paid to the good contact between the bottom of the relay and the heat sink, and consider applying an appropriate amount of thermal grease to achieve heat dissipation. If the relay works at high temperature for a long time (40°C-80°C), the user can consider derating to ensure normal operation according to the large output current and ambient temperature curve data provided by the manufacturer.

How to match the user's drive circuit with the input characteristics of the solid state relay

　　Causes of Solid State Relay Heating:

When the solid-state relay is working normally, there is a certain power loss on its internal chip, and this loss power is mainly determined by the product of the output voltage drop of the solid-state relay and the load current, which is consumed in the form of heat. Therefore, the quality of heat dissipation directly affects the reliability of the solid state relay, and the excellent thermal design can avoid failure and damage caused by poor heat dissipation.

When the relay is used, the internal output of the SSR solid state relay will be damaged due to overcurrent and load short circuit, and the quick fuse and air switch can be considered in the control loop for protection (the output protection of the product should be selected for the relay, and the built-in varistor absorption loop and RC buffer can absorb the surge voltage and improve the dv/dt tolerance); Fast fuses and air switches are a universal method of overcurrent protection. The fast fuse can be selected at 1.2 times the rated operating current, and the fuse can be selected for small capacities. Pay special attention to short circuits in the load, which are the main cause of damage to SSR products.

For inductive and capacitive loads, in addition to the internal RC circuit protection, it is recommended to use a varistor in parallel at the output as a combination protection. The area size of the metal zinc oxide varistor (MOV) determines the absorbed power, and the thickness determines the protection voltage value. AC 220V SSR, MYH12-430V varistor; MYH12-750V varistor is selected for 380V; For larger capacity motor transformers, MYH20 or MYH2024 varistors with large through-current capacity should be selected. The selection principle is 500V-600V varistor for 220V, and 800V-900V varistor for 380V.

Application examples

Pressure regulation applications

SSR, TSR voltage regulating module, can use an external analog signal to trigger the module to achieve linear adjustable output voltage. For example, a PLC or thermostat outputs an analog signal: a trigger system of 1-5V, 4-20mA. The domestic single-phase three-phase thyristor trigger board, with the thyristor, can also be equipped with an external analog signal to adjust the trigger board, and the trigger board can then trigger the module to achieve linear adjustable output voltage and control the conduction angle of the thyristor to achieve the purpose of voltage regulation.

AC power adjustment

"AC power regulation" is a commonly used method for Z-type SSR, which can also achieve PID regulation. That is, in a fixed period, the number of half waves of AC sinusoidal current is controlled to achieve the purpose of power regulation. Analog circuits often use a voltage comparator to compare the sawtooth voltage for a fixed period with the error voltage from the pre-stage, and the output square wave is adjusted, as shown in Figure 3. The timing algorithm is used on the computer to generate a square wave pulse impact with adjustable duty cycle. For example, Japan's SHIMADEW and OMRON company's SR22, FD20, E5 series intelligent temperature control products, with Z-type SSR, to achieve adaptive "automatic flip" control, that is, through the computer to generate disturbances, calculate PID control parameters.

Three-phase current

HS series SSR products can be directly used for the control of three-phase motors. The simple method is to use 2 SSRs for motor on-off control, 4 SSRs for motor commutation control, and the third phase is not controlled.

When commutating as a motor, it should be noted that due to the inertia of the motor, it must be reversed only after the motor is stopped, so as to avoid a large impulse voltage and current caused by a similar motor stall situation. In the design of the control circuit, it should be noted that the possibility of simultaneous conduction of commutation SSR should not occur at any time. The timing of the upper and lower power should be used to add and then break the power supply of the control circuit, and then add the timing of the power supply of the motor to break first. The inverter connection mode cannot be simply used between the commutating SSRs to avoid the phase-to-phase short circuit accident caused by the conduction of the SSR of the other phase when the conduction SSR is not turned off. In addition, the safety, phase loss and temperature relays in the motor control are also protective devices to ensure the normal operation of the system.

How to match the user's drive circuit with the input characteristics of the solid state relay

Sections viewed

Contact

working hours