DC loads up to 2 amps as voltages from 6 to 15 volts can be found by this high sensitivity solid state relay.
These loads can be bulbs, motors, solenoids, heating elements, electromagnets, etc.
Common relays can be replaced by this circuit in many robotics and mechatronics designs.
The sensitivity of the circuit is large enough for sensors such as phototransistors, LDRs, thermistors, etc. Can be used directly to control high current loads.
The sensitivity adjustment is done in P1 since the circuit based on a power field effect transistor (Power FET) is extremely sensitive.
The transistor conducts when the voltage between E1 and E2 becomes sufficiently positive to saturate it.
A resistive sensor will be connected between E1 and the positive supply.
The circuit can also be controlled directly by TTL and CMOS outputs which allows its use in interfacing robotics and mechatronics projects with computers.
In figure 1 we have the complete diagram of the solid state relay for currents up to 2 amps.
The arrangement of the components on a terminal strip is shown in figure 2.
The transistor must have a heat radiator, especially if it is used with current above 1 amp.
The resistors are 1/8 W or larger and the capacitor must have a working voltage slightly higher than that used in the power supply.
At points A and B we connect the load to be controlled and between E1 and E2 or even E1 and the positive of the power supply, the sensor or the excitation signal source of the circuit.
If the load is inductive (motors or solenoids) it is convenient to connect a protection diode in parallel, polarized in reverse direction (cathode or band) connected to the positive of the power supply.
Check the operation of the relay, only use it.
Parts List
Semiconductors:
Q1 - IRF620 or equivalent - any power FET with more than 2 A of drain current
Resistors: (1/8 W, 5%)
R1, R2 - 10 k ohms - brown, black, orange
P1 - 1 M ohms - potentiometer
Capacitors:
C1 - 1000 uF - electrolytic
Miscellaneous:
Antenna / ground terminal block for input and output, heat radiator for transistor, mounting box, potentiometer knob, wires, solder, etc.
