A transistor optocoupler is usually used to control a low-voltage relay (up to 50 V) – see Figure 5.8 . Figure 5.7 – Scheme of connecting load to the output of type Р CAUTION The diode VD1 (KD103 or similar type) should be installed in parallel to the relay coil, in order to avoid failure of the transistor due to the large self-induction current. Figure 5.8 – Scheme of connecting load to the output of type К The optosimistor is connected to the control circuit of the power triac through the limiting resistor R1 according to the scheme shown in Figure 5.9 . 27