Delay switch made with LM431

Generally, the delay switch circuit is made of NE555, but its maximum working voltage can only reach 18 volts. Some customers require a delay switch circuit that can work at 24 volts for delayed ignition of cars. I designed a delay switch circuit using LM431, which can work at 24 volts and meet the customer's requirements. The electrical schematic is as follows:

R1 and C1 form a delay circuit. The delay time is required to be 1 second. C1 should be a tantalum capacitor that can work at -55 to +125℃. After power-on, the input of LM431 is low level, the output is about 23 volts, Q1 and Q2 are turned on, the ignition coil is powered for a short time, and the current is about 24 amps. One second after power-on, the input of LM431 rises to 2.5 volts. Since the output of LM431 is about 2. volts at this time, a voltage regulator Z2 with a voltage value of 6.2V should be connected in series at its output, so that Q1 and Q2 can be turned off and the ignition coil loses power. The ignition coil is an inductive load with a DC resistance of about 1 ohm and a 24-volt battery as the working power source. The measured current is about 25 amps. The operating temperature range of this circuit can reach -40 to +121℃, which can fully meet the requirements of automotive electronics.