Timeline for PNP transistor turns on at 3.3v
Current License: CC BY-SA 4.0
6 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Mar 10, 2019 at 21:21 | comment | added | analogsystemsrf | If you don't specify the buzzer's current, then the transistor can only be driven iinto saturation. Try a 1Kohm pot, in series with 100 ohm resistor to ensure base current will not exceed (5v - 0.7v) / 100ohm = 43mA. That scaled by 10X to ensure saturation of the 2N3906, allows 430mA (0.43 amp) thru the buzzer. If the buzzer is a relay-type, you need a 0.1uF across the buzzer to absorb inductive spikes, otherwise the 2N3906 will be destroyed. And, attach the 2N3906 base to wiper of the pot. | |
| Mar 10, 2019 at 14:23 | comment | added | Praveen | Anyone has a circuit with only resistors? I have added a pot to base as a pull-up to get right resistor value. But it does not seem to work. | |
| Mar 10, 2019 at 14:21 | comment | added | analogsystemsrf | Rail bounce of either +3.3 or +5 will allow intermittent triggering of the transistor. | |
| Mar 10, 2019 at 14:16 | comment | added | Edgar Brown | Why bother with the diodes (at least so many of them) when the resistors can be selected to provide the right voltage? | |
| Mar 10, 2019 at 14:14 | comment | added | Praveen | what are the three diodes for, may I ask? Is is to reduce voltage by 2.1? | |
| Mar 10, 2019 at 14:11 | history | answered | analogsystemsrf | CC BY-SA 4.0 |