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Transistor as switch

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tiwari.sachin

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I have a input to the transistor that will be 5V or 0V and I want to switch the output to 24V or 0V

ie.

when input = 5V, Output = 24V

when input = 0V, Output = 0V

Suggest how I can do this. This 24V output will be used to drive the relay.

Max current requirement to drive the relay shall be 200mA. The input to the transistor circuit will be given via PIC16F877A
 

andre_teprom

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You can use a PNP one :

npn-pnp.png



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tiwari.sachin

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Andre,

I too thought about the same thing but was keen if I can use a single component to do so.
 

andre_teprom

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You can use that, however uC output will be more susceptible to burn due to spike generated by relay coil :

low-side.png


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tiwari.sachin

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I am designing a board that will be used with general purpose relay boards available here so I need to control the positive signal of the relay and not the ground. I guess first option is more suitable but with increase in BOM cost.

By the way, there would be a flyback diode that will take care of spikes.
 

andre_teprom

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Won't a diode across the relay coil take care of the spike?

Depending on load at relay contacts, sometimes, neither a by-pass capacitor connected between VCC and GND is not enought to ensure that.

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