| ??? 05/01/09 11:59 Modified: 05/01/09 12:42 Read: times |
#164985 - 0.1A Responding to: ???'s previous message |
When designing a circuit like this the "about 0.1A" is a bit of a concern. You need to be aware of the maximum current so as to select components that can survive the worst case current surges. A very necessary piece of data is the DC resistance of the solenoid coil.
You could replace the two 2N3055s with a TIP120 but when doing so then consider also purging the 150 ohm resistor that I showed going to GND. The TIP120 has built in base-emitter resistors on each transistor (which is one reason I dislike the component). You may also very likely need to adjust the resistor I showed as a 15 ohm value based on the current it takes to saturate the darlington. If the solenoid current is low as you state and the maximum current is not too many times more than that you may want to consider not using a darlington. A darlington always has a higher saturation voltage across the output that raises the power dissipated in the component. There should be plenty of low cost NPN power transistors to pick from that can drive a 100 mA solenoid in a circuit like this and achieve a driver saturation much lower than a half of a volt. Michael Karas |
| Topic | Author | Date |
| Driving TIP120 from 8052 | 01/01/70 00:00 | |
| It is the Current | 01/01/70 00:00 | |
| Use this type circuit | 01/01/70 00:00 | |
| Thanks, I'll give it a try | 01/01/70 00:00 | |
| 0.1A | 01/01/70 00:00 | |
| Michael circuit is fine with some diff values. | 01/01/70 00:00 | |
| Success! | 01/01/70 00:00 | |
You use a Darlington, ... | 01/01/70 00:00 | |
| Check values | 01/01/70 00:00 | |
| is Q2 not a bit overkill? | 01/01/70 00:00 | |
| Base current and transistor beta | 01/01/70 00:00 | |
| logic level MOSFET | 01/01/70 00:00 | |
| they do make p-channel logic mosfets | 01/01/70 00:00 |