TLP3547 Evaluation Board Review [Replacement of Mechanical Relays][Copy link]
This post was last edited by wenyangzeng on 2018-9-9 08:08 TLP3547 Evaluation Board Review [Replacement of Mechanical Relay] This TLP3547 uses LED to replace the electromagnetic coil of the traditional mechanical relay. The output terminal is controlled by lighting the LED. It can directly replace 5V, 12V, and 24V mechanical relays. Refer to "Toshiba Photorelay Mechanical Relay Replacement Evaluation Board" to know that the LED power supply circuit on the circuit board limits the maximum forward current of the LED by connecting a 1.5K ohm resistor in series. Before the formal replacement, we decided to test the current of the LED circuit under different working voltages. The test results are as follows: 5V: 2.3mA 12V: 6.9mA 24V: 14.5mA Table 1 From the test results, we can see that as the power supply voltage changes from low to high, the current of the LED also changes from small to large. This situation will cause the internal resistance of the output MOS tube to increase and heat up when the power supply voltage is low, because the current flowing through the LED is small. Therefore, it is recommended to replace the current limiting resistor with different resistance values according to different working voltages. The working motherboard power supply voltage of this evaluation is 24V and the working current is about 2A. The power supply on-off control uses Panasonic 12V mechanical relay. The working voltage of the relay electromagnetic coil is reduced from 24V to 12V through the voltage regulator IC (Figure 1). From Table 1, it can be seen that the working current of the LED is 6.9mA when the power supply is 12V, which is a relatively suitable current. The working conditions of this board are very suitable to be directly replaced with the TLP3547 evaluation board. See Figure 2 for the schematic diagram of the modified circuit, and Figure 3 for the actual picture.
Figure 3 After the modification, the power is turned on and it works normally, and the effect is satisfactory. If its price is not much different from that of a mechanical relay, the replacement will further save the occupied area of the PCB board. And the service life will be greatly improved. After 10 minutes of power-on, the TLP3547 heats up slightly. It seems that the heat dissipation of the TLP3547 needs to be improved. Speed test: Since a 3300uF large-capacity electrolytic capacitor is connected to the target board, the +24V rise time is delayed after power-on, so this test is meaningless, see Figure 4.
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