I need to generate a current signal between 12V and GND, which has to have galvanic isolation. For this, I want to use an optocoupler.
- Maximum permittable rise / fall time: < 1µs
- Output side Vcc: 12V-14V
- Output current: > 28 mA
Because of the high output current, an external transistor is required, since most optocouplers that are fast enough are limited at around 16 mA. This allows the use of open collector optocouplers, driving a PNP transistor.
The PNP transistor then pulls a line to ground, which bypasses a resistor, increasing the current signal.
Can I use this open collector output to drive a PNP transistor (with an appropriate base resistor) without using a dedicated pull-up resistor?
There are also biased PNP transistors which include a pullup, but those are mostly (only?) available as SMD parts, while I would like to keep using THT.