Single Coil Latching Solenoid

[djbunting]

I have kludged together a system to control single coil latching solenoids for remote control and I am looking to further the project and roll my own solution.

The specs for solenoids I am controlling are as follows:

Voltage: 9 - 12 VDC
Resistance: 4.2
Switching Time: 25-50 msec

The system runs on a 12v sla battery
The mcu can source a maximum of 4mA at 3.3V

Currently I use this circuit to control the solenoids with a single mcu io using an onboard relay and a 4700uf capacitor.




After a lot of browsing I have determined the below circuit to be the simplest I can find to do a similar operation without a relay. Note solenoid coil is the 100ohm resistor under cap


What I would like to know is what specs I need for the transistors to drive a solenoid of the above specs

Or is there a simpler ? more elegant? more reliable solution?

I appreciate any help you can give me thank you very much in advance.

Long time amp hour / eevblog listener first time caller?

[German_EE]

Where is the relay coil in your schematic?

[djbunting]

Sorry should have mentioned that solenoid coil is the 100ohm coil under next to the 220uf cap

Thank you