555 (TLC555) Relay Driver Circuit Multiple integrated circuit topographies are undocumented features or functionality. He is one of them. TLC555 open output (PIN 3) open-drain transistor load 100mA sink v. 1.28 (PIN 7) 100mA sink 1V is reset. To connect, it is permissible, because they do the same, and potentially double the current features of the receiver of 200mA. It is the perfect place for the 133mA the relay coil to do. Income is also a Schmitt trigger, but better known positive making the transition without papers under the name of a feature. 555 Relay Driver Schematic Protoboard setup Output current rating (pin 3): TLC555 vs. NE555 (Vcc = 15V) TLC555 NE555 Source current 10mA 200mA Source mode saturation voltage Vcc-0.8V Vcc-2.5V Sink current 100mA 200mA Sink mode saturation voltage 1.28V 2.5V At the same time, if you keep a higher current consumption is the 555 and the saturation voltage is very small is, unfortunately without excessive voltage drop in the truck. Also shows that there are many, like for example TTL TLC555 acquisition ability is much smaller than the absorbing capacity. To drive a relay, but we are only interested in flow properties. This is a 40A automotive relay (contactor) that I selected for this application. Since its coil current exceeds the TLC555 output sink current rating, it is a good candidate. Manufacturer or part number is unknown. Contact rating: 40A (from memory) Coil resistance: 90Ω cold Coil current: 133mA Coil power: 1.6W Coil voltage: 12V Pickup voltage: 4.8V cold Dropout voltage: 2.1V cold Operate time: 4.5mS What is the difference between a relay and contactor is? There is no clear distinction between say the current level and/or the application - for me, it is something for 20A relay signalling device. What does it cost 40 or more, or the power of applications is also a subcontractor. Schmitt trigger input Input (pin 2) and limit the value of the input (6-pin) pins are connected - it's more to do. 12V, the upper bound is smaller than the 8V and 4. Two levels of voltage, which is not nearly as Schmitt trigger. This can be directly attributable to the 4000series that CMOS logic, which also works with 12V. To compatible with TTL logic levels the two resistors in the schema to add. It loads the internal divider, the voltage will be lower. Calculated in accordance with the approximately 1.4 and 2.8 V. Testing the performance Output saturation voltage: o 0.617V @ 133mA o 1.043V @ 200mA TTL high level threshold: 3.0V TTL low level threshold: 1.6V How about the bipolar 555 and other variants? The standard 555 saturates poorly (2.5V) at 200mA and its reset line (pin 7) is not specified above 15mA, so it is not recommended. The intersil 7555 is a very low power device, so that is not recommended either. For the future Assorted relay driver circuits. 555 Voltage doubler relay driver circuit. Relay economy circuits.