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Can a transistor be used as a relay?
A transistor is an electronic device that can work as a switch. It allows control of a large current by a smaller current as does a relay. When you apply positive voltage to the base of an NPN transistor, it turns on the collector-emitter connection and allows current to flow from collector to emitter (Figure 6).
Why use a relay instead of a transistor?
Typically, they use an electromagnet reed switch to allow a small electric signal to switch much higher voltages. Relays are distinct from transistors in a few key ways. – Relays handle much higher current and voltage loads. – Relays can switch loads regardless of the device’s internal circuitry.
Which transistor is used in relay module?
NPN transistor switch
A typical relay switch circuit has the coil driven by a NPN transistor switch, TR1 as shown depending on the input voltage level. When the Base voltage of the transistor is zero (or negative), the transistor is cut-off and acts as an open switch.
Can a transistor drive a Raspberry Pi relay?
Raspberry Pi GPIO: Driving a Relay using a Transistor. A transistor usually drives a relay by energising its coils. The relay contacts can then switch higher voltages and currents, which the transistor cannot manage directly.
How big of resistor do I need for bipolar transistor?
For a bipolar transistor – that is driven by current not voltage – a series resistor between the GPIO pin of the Pi and the base of the transistor is recommended. This is typically around 10 kOhm (see here, R1).
What kind of transistor does a GPIO use?
Assuming that the output drive current from the GPIO pin is a conservative 4 mA, the relay coil is a 5 V type with a resistance of 69.4 Ω, a suitable transistor is one that has an Ic rating greater than 72 mA, and hFE greater than 90.
What kind of current does a GPIO relay need?
These relays are typically available in 5 V, 9 V, 12 V, 24 V, and 48 V, coil versions. To energise the relay coil it must have sufficient “pull-in” current passing through it, therefore, the voltage must be precise. The table above shows the coil resistance and the current requirement for each relay.