#7 SEGMENT COMMON ANODE DRIVER#
The fact that you can find both types of displays on the market - still - shows that there isn't agreement on which is better.įor a single digit, it likely doesn't matter (CA or CC) so long as the driver you intend to use matches what the display requires. The 4511 is designed for good high-side drive.
You should carefully search for an inverter meant for high-side driving. Many TTL inverters only weakly provide drive current to a common-cathode LED display.
#7 SEGMENT COMMON ANODE SERIES#
You couldn't drive a common-anode LED display from inverter outputs, but you could drive a common-cathode LED display through seven series resistors from inverter outputs. Seven inverters at all seven 7447 outputs? Possibly, but a well-engineered circuit would include seven pull-up resistors to +5v at 7447 output pins. Inverter at the four 7447 BCD logic inputs? Simply - No! But the same current-limiting method is used to drive LED displays (from a data sheet acquired from Harris Semiconductor SCHS072B - Revised July 2003):Įxtra question: Could I use a NOT gate on the common anode to make the The 4511 seven-segment driver is a different animal, not only because it is meant for common-cathode displays, but because it is based on hybrid CMOS/BJT logic. Brilliance is adjusted by substituting other resistor values - brilliance is almost proportional to current. Some LEDs are super-bright while others (perhaps older) are not. If you decide that 5mA LED current provides a bright-enough display, then each of seven series resistors would be 2.8V/5mA = 560 ohms. The 7447 internal transistor adds a few hundred millivolts to this, leaving perhaps 2.8V for each series resistor to soak-up. Each LED of a common-anode array needs at least a few volts to even begin to light up. Since this chip wants a +5v DC supply, LED common-anode pin is often connected to +5V as well. Simulate this circuit – Schematic created using CircuitLab Generally, each of a,b,c,d,e,f,g output pins gets a similar-value series resistor to limit current. I've never seen this chip used without current limiting resistors, when driving LED seven-segment display. It's not enough for a large display and certainly not for a scanned display connected in a matrix. That's fine for a small display with individually driven lines. Again, you need resistors and the inverter can only drive a few mA. (Image source: Answer from Sachin Pathave to the question "How can we connect 7 segment display with IC 7447?" on Quora)Ĭould I use a NOT gate on the common anode to make the inputs "1" turn the LEDs on? But be aware that the 7447 IC is only capable of driving a few mA. 7 resistors, such as 330 Ohm, each in series with each line between the IC and the display. If in a matrix, it depends on whether you're scanning the anodes or the cathodes.ĭo I need resistors here? Where would I connect them? If individually, common anode is easier because N-polarity devices (N-channel MOSFETs, NPN BJTs) are more common and perform better for a given size and price. If you're spinning your own circuit (no specialized IC) using external transistors to carry the current, then it depends on whether you're driving the segments individually or in a matrix. If you haven't picked a chip, then the consideration is the cost and availability of parts. The only consideration is which chip you're using. What are the considerations of using a common anode 7-segment display over a common cathode?
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