Negative Voltage to Switch Transistor without Inverter

Negative Voltage to Switch Transistor without Inverter#164186

By engr - Sat Oct 05, 2013 9:57 pm

- Sat Oct 05, 2013 9:57 pm #164186

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Last edited by engr on Sun Apr 10, 2016 4:25 pm, edited 1 time in total.

Re: Negative Voltage to Switch Transistor without Inverter#164187

By waltr - Sun Oct 06, 2013 8:56 am

- Sun Oct 06, 2013 8:56 am #164187

You can't. If you need a Voltage that is negative to ground then you need some type of inverter circuit. There are a few small chips that can supply a few mAs at -10V. The ILC7660 is one I use but a MAX232 can be used. There are also 555 circuit to produce a negative.
Exactly how are you wiring this? +5V to LED to resistor to MOSFET Drain to MOSFET source to Ground?
What MOSFET are you using??
There are MOSFETs that have Logic level gates that eliminate the need for a negative supply.

Re: Negative Voltage to Switch Transistor without Inverter#164224

By Valen - Mon Oct 07, 2013 10:16 am

- Mon Oct 07, 2013 10:16 am #164224

Could be that the OP has a P-mosfet, as than needs a negative gate voltage wrt source. So yeah, what mosfet are we talking about?

Re: Negative Voltage to Switch Transistor without Inverter#164227

By Mee_n_Mac - Mon Oct 07, 2013 12:49 pm

- Mon Oct 07, 2013 12:49 pm #164227

One way might be use an opto-coupler. It could switch ~5v to the gate of a FET used as a low side switch. (assuming the -10v isn't really hardwired to the gate as stated in the OP)

Depending on the LED current you might eliminate the FET.

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