How Can I Use a Transistor to Drive a Relay with a Negative Output?

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In summary, the person is seeking advice on how to use a negative output from their circuit to drive a relay that requires a positive output. They are considering using a transistor but are unsure if they need a PNP or NPN. They mention a helpful resource and suggest using a PNP and NPN transistor in series to achieve the desired result.
  • #1
triden
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Hey guys,

Right now I have a circuit designed and seems to work fairly well. Now the output from my circuit is a negative output and I need it to drive a relay. The relay I am using says it draws about 100mA and my chip will output 50mA max. I figured I would put a transistor on the output to drive my relay...the only problem is that the output is negative. In this case I am not sure what to do. Do I need an PNP instead of an NPN?

So far I figure the IC neg output goes to base, emitter to ground side of coil and collector to ground rail of circuit...but I don't think this will trigger because the base is negative.

Thanks for your suggestions
 
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  • #3
If your circuit pulls low, drive a PNP transistor in series with an NPN transistor, which pulls low again at a higher current.
 

FAQ: How Can I Use a Transistor to Drive a Relay with a Negative Output?

1. What is a transistor?

A transistor is a semiconductor device that is used to amplify or switch electronic signals in electronic circuits. It consists of three layers of a semiconductor material, typically silicon, with each layer being doped to create an n-type or p-type region.

2. How does a transistor work?

A transistor works by controlling the flow of electrons between two of its layers. When a small current is applied to the first layer, called the base, it allows a larger current to flow between the other two layers, called the emitter and collector. This results in amplification or switching of the electronic signal.

3. What are the different types of transistors?

There are two main types of transistors: bipolar junction transistors (BJTs) and field-effect transistors (FETs). BJTs use both electrons and holes as charge carriers and have three layers, while FETs use only one type of charge carrier and have four layers.

4. How do you solve a simple transistor problem?

To solve a simple transistor problem, you first need to identify the type of transistor and its configuration, which can be either common-emitter, common-base, or common-collector. Then, you can use the appropriate equations and circuit analysis techniques to determine the output voltage and current.

5. What are some common applications of transistors?

Transistors are used in a wide range of electronic devices, including computers, televisions, radios, and mobile phones. They are also used in power amplifiers, switching circuits, and digital logic circuits.

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