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Tip - ULN2003 High Power Driver

2014-11-27 22:04  
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The ULN2003 is a very cost effective chip that acts like a switch. The easiest way to explain its operation: It simply switches an earth to/from an external circuit, and can withstand a continual500mAcurrent drain and a maximum50V. All this for $0.47 AUD.


ULN2003 internal picture

What's Inside?

The picture on the right is what the ULN2003 looks like internally.

Pins 1:7 are inputs, while pins 10:16 are high current sink drivers. Between the I/Os is an independentDarlington pair(the 'Darlington pair' behaves like a single transistor with a high current gain). When an input is driven high, the corresponding output will basically become an earth. Alternately, when the input pin is low, the output pin adopts a high impedance.

This allows external high-current circuits to be driven by small micro-controllers. There are seven channels ready to be used, and as mentioned earlier, the ULN2003 can sink up-to 500mA between all the channels.



There is onlyone power connection, a common ground (Pin 8). Here's an example of driving a high power LED with logic voltages via the ULN2003 (note the LED is being driven by a 12 volt source, but controlled by the logic voltage);


Forinductive loads, such as motors and relays,Pin 9is connected to the loads+Vto shuntcounter-electromotive force(EMF, also known as CEMF) safely. That is, if the motor was connected to +12V and thenpin 16of the ULN, thenpin 9would be connected to the same +12V source as the motor.

The ULN2003 has become my primary choice to controlling external components - its cheap, effective, and requires no operating voltages other than thecommon ground. Keep in mind that you will have a voltage drop of about0.9v-1.0vover the UL2003 when in circuit.