Controlling relays with logic gates

Question

Pretty new to electrical engineering world, so probably rather simple question. I´m designing control system for tractor trailer hydraulic system. The system is 12 V and solenoids what I am using there are 2 A. Also I´m using few digital inductive sensors(IFS241) which output also 12 V. Since There are some logic behind the operations, I was thinking to use 18 V AND CMOS logic gate (NTE4081B) and 20 V NOT CMOS logic gate (CD4069UB) to run relays. But here is the problem that logic gate outputs only 500 mW and already one relay needs 400 mW (DS1E-M-DC12V). Do you have some ideas how to boost this signal, or how I should control the relays with logic?

Thank you for you advice.

Answer 1

To replace some simple logic such as CD4069UB with higher drive, you can use transistors. Such as MOSFETs or BJTs. Even the most basic transistors can give you power of 400 mW or more. This way, you can control the amount of output power you can drive by choosing a transistor (output current limited by open channel of transistor). If you drive relay when the output of inverter is high, you should take P channel inverter ( PMOS inverter on the picture). If you drive them low, you can use N side inverter. If however you need to have low output impedance on both LOW and HIGH output, use CMOS logic (P and N transistor). Here are all representations of inverter with BJT or MOSFETs. To drive the output of an AND gate, you can invert its output and then use the output inverter as before as a buffer. Also, don't forget to add diodes if you want to control an inductance load. More info here.

Answer 2

Provided that the logic is simple, the task may be easily accomplished using relays alone.