Fig. 1 Tri-state buffer schematic.
Non-Inverting Tri-State Buffer-Switch Demo Circuit
This page demonstrates using a single integrated circuit with 2 MOSFET output transistors.
Fig. 1 illustrates using a single CD4011 integrated circuit with quad (4), 2-input NAND gates. A CD4011 operates from 3-15 volts.
CD4011B and CD4011D operate is inverters - HIGH in = LOW out and vice-versa.
Fig. 2 Tri-state MOSFET output buffer truth table.
Fig. 2 is the truth table for the circuit in Fig. 1. What is not shown in Fig. 1 is the voltage connections for the CD4011 and +Vcc.
Fig. 3 CD4011 Pin Connections
If this circuit is connected to 5-volts then direct connection to a microcontroller such as PICAXE, Arduino, and PIC are simple direct connections.
When the gate to Q1 LOW, Q1 will turn on. When the gate of Q2 is HIGH, Q2 will turn on.
Both Q1 and Q2 must never be turned on at the same time!
If we use a 12-volt motor, etc. then the CD4011 voltage must also be 12-volts. The problem is direct connection to a 5-volt microcontroller won't work.
That requires a separate interface circuit. Q2 can remain as it is, it's the Q1 circuit that is the problem. I'll assume a 5-volt supply for the digital circuits.
Fig. 4 Tri-State switch with NPN transistors for higher voltage output.
Fig. 3 illustrates the use of 2 NPN bipolar transistors and 3 resistors for higher voltage output. Remember +Vcc is NOT the 5-volt supply for the digital circuit. This is the output voltage that can't exceed Vgs of the P-channel MOSFET.
The truth is identical to Fig. 2.
For more on power MOSFET switches see the following:
- Tutorial NOR Gate SR Latch Circuits
- Tutorial NAND Gate SR Latch Circuit
- Basic Digital Circuits Tutorials
- High current TTL MOSFET Driver Circuit
- Non-Inverting Tri-State Buffer-Switch Demo Circuit
- Review Connecting Digital Logic and Transistors
- From SR Latch to Microcontroller IO Pin Introduction
- Transistor-MOSFET Switch Circuit with Optocouplers
- High Voltage Optocoupler Tri-State Switching Circuits
- Optocouplers for TTL-CMOS Logic Level Shifting
- Basic TTL Tri-State Buffer Circuit Example 1
- Basic TTL Tri-State Buffer Circuit Example 2
- Transistor Output Non-Inverting Tri-State Switch
- Transistor Output Inverting Tri-State Switch
- Tutorial OR-NOR Circuits Including Monostable Multivibrator
- Introduction to RC Differentiator Circuits and Uses
- Brief Tutorial of XOR and XNOR Logic Gates
- Simple Schmitt Trigger SN7414 Square Wave Generator
- SN7414 Square Wave Generator uses SN7476 JK Flip-Flop
- Three Output Pulse Generator Circuit for Digital Circuits
- Geiger Counter Adventures in Radioactivity
- Introduction to Geiger-Mueller Counters and Electronics
- Astable CD4047 Geiger Counter Power Supply
- CD4047 Monostable Multivibrator Circuit
- Getting Real About Radiation Myths and Hazards
- Uranium Hype-Facts and Virginia Uranium
- Uranium Basics and Isotopes
- Climate Change, Climate Scams, and Volcanoes