Microcontroller Output Control Arnan Sipitakiat Dept Compute Engineering

Microcontroller Output Control Arnan Sipitakiat Dept. Compute Engineering, Chiang Mai University

What’s wrong with this circuit? A microcontroller usually supplies limited current (i. e. 25 m. A). This is ok for LEDs but not enough for high current loads like a motor

Transistors Using transistors as a switch Transistors works both as (1) a switch and (2) a current amplifier. Transistors allow us to send higher current to a load.

Using a transistor

Different Loads Requires Different Power Typical LEDs 5 -15 m. A @5 V Or 25 -75 m. W Small DC Motors 100 -200 m. A @5 V Or 0. 5 -1 W Irrigation Control Valve 0. 6 -1. 0 A @24 V Or 14 -24 W

Can the 2 N 3904 control the valve? Irrigation Control Valve 0. 6 -1. 0 A @24 V Or 14 -24 W

The answer is in the datasheet

1. Control 24 V? -> Yes 2. Can supply enough current? -> No. • At 24 V, the maximum current is 625/24 = 26 m. A • Notice that 26 m. A is a lot less than 200 m. A • 200 m. A can be achieved only at 625/200 = 3. 125 V

How about this one? KTD 882

1. Control 24 V? -> Yes 2. Can supply enough current? -> No. • At 24 V, the maximum current is 10/24 = 0. 416 A

This one? ST-13005

1. Control 24 V? -> Yes 2. Can supply enough current? -> Yes. • At 24 V, the maximum current is 75/24 = 3. 125 A • 75 W can be achieved only when Tc (case) is 25 C.

Heat sinks are very important when driving high-current loads It keeps Tc within range

Higher loads Drone Motor 14 -25 A

Relays Usually have higher current ratings for its price. 15 -50 Amps @5 V typical for less than 100 THB

Relay “Poles” and “Throws”

Driving load with a relay

Solid-State Relays

H-Bridge: A bi-directional driver

Relay H-Bridge

Transistor H-Bridge

H-Bridge IC / Module

Power Supply? Max. current 0. 5 A (USB 2. 0) 0. 9 A (USB 3. 0 & 3. 1) 3 A (USB Type-C)

Wall Adapters Voltage and Current is defined on the package Typical values: 5, 9, 12 V and 0. 3 to 3 A

Switching Power Supply Voltage and Current is defined on the package Typical Values: 5, 12, 24 V and 2 to 50 A

Batteries (Alkaline) Theoretically can supply unlimited current within its capacity (~1500 m. Ah for AA). In practice, can give about 2 -3 amps.

Other types of batteries Li-ion (Lithium ion) LIPO (Lithium Polymer)

Conclusions �There are many ways to drive output devices �Transistors are good for low power applications �Relays are suitable for AC power applications or when low loss and high current is needed �H-bridge is for bi-directional applications �Choose the right tool for the job!