Electronic – Gate Output as a Switch

The first comprehensive logic series was the TTL series 74xx. This used BJTs (Bipolar Junction Transistors). Later there came variants like the often used 74LSxx, where the "LS" stands for Low-power Schottky TTL. As the name implies these used less power than the rather power-hungry TTL, and were faster too. At the same time the CMOS 4000 series was developed. The "C" in CMOS stands for Complementary, meaning it's a combination of N-channel and P-channel MOSFETs. Their construction is simpler than TTL and they use far less power. Later standard CMOS developed into HCMOS, "H" for High-speed. Most 74LSxx types have been released as HCMOS in the 74HCxx series, or the 74HCTxx series, which is TTL compatible. Later more variants were developed, like Advanced CMOS (74ACxx).

Microcontrollers are built in HCMOS technology, so they use MOSFETs. AFAIK JFETs aren't used for logic ICs. The transistor you show in the picture is a BJT, which you can tell from the pin designation:

E = Emitter
B = Base
C = Collector

For a MOSFET the pins would be

S = Source
G = Gate
D = Drain

respectively.

Many ICs in the 74HCxx series were originally released in 14 or 16 pin DIL packages, which meant that they would fit four 2-input gates. With miniaturization (SMT) came the demand for smaller packages, even if they contained less gates. Several manufacturers offer single-gate and dual-gate versions of logic gates. For example, NXP has a 74LVC1G00 (single 2-input NAND) and a 74LVC2G00 (dual 2-input NAND) version of the classical 74HC00. 74LVCxx is yet another HCMOS technology. This page lists all NXP logic families.

While @JimDearden's answer provides a suitable approach for operating the two infrared LEDs in parallel as desired, my answer addresses the specific question asked, to resolve some possible misunderstandings that may have motivated the question:

• An AND gate is used for taking two or more inputs, and providing a single output representing the logic AND operation on those inputs. The purpose underlying the question is the opposite: To take a single input (from the Arduino pin) and drive two outputs. Hence, no rationale for using an AND gate

• The classic 7400 series TTL logic gates have recommended operating conditions of merely 16 to 22 mA per output (current sink) depending on manufacturer. See the 7408 AND gate for instance. In other words,

  1. They will not sink enough current for two IR LEDs if the output is used as a low-side switch, with the LED between output and the (presumably) 5 Volt supply. (actually they will sink up to 55 mA in short-circuit, but that is beyond recommended safe operating area)
  2. Many 74 series gates will not provide a high side output of any significance for turning on LEDs connected between output and ground - they are designed to be used with a pull-up resistor on the output pin.

  _{Note that some variants of the classic 74 series logic parts can both sink and source current, and there are even some that can deliver outputs in the ampere range. For instance, the 74595 shift register has an equivalent, the TPIC6595, which sinks 1.5 Amperes pulsed current per pin.}

• If the intention is to operate LEDs from the output of a 74 series gate, this won't work the way the output of the Arduino works: The LEDs would have to be connected on the Vcc side, with cathode at the logic gate output, and the output logic will need to be inverted in code.

So, in short, the 7408 AND gate is neither a viable nor a justifiable approach to solving the problem.