High Current Tri-State MOSFET Driver Circuit


This will serve as an introduction to Tri-State power driver circuits. This is oriented towards H-Bridge motor controls.

The circuit reviewed here is not tri-state, but high-low output depending on the input. The input will be not inverted.

TTl to CMOS interface circuit.
Fig. 1a

While I use a Vcc of 5-volts if the input inverter is CMOS Vcc has a range of 3-15 volts. That requires a 5 to 15 volt interface circuit like that in Fig. 1a.

The ultimate goal is the H-Bridge shown as hb_big2.jpg

High current TTL driver circuit.
Fig. 1b

Fig. 1b uses an open collector 75LS06 with a pull up resistor. See Review Connecting Digital Logic and Transistors

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HIGH is +5V and LOW is 0V unless specified otherwise. This assumes a 5-volt microcontroller.

The concept here is to drive heavier loads from a microcontroller I/O pin. Most are limited to 25-40mA This circuit can source-sink several amps.

High current TTL driver circuit.
Fig. 2

Fig. 2 circuit is non-inverting. HIGH in is HIGH out. LOW in is LOW out. When DIN is HIGH the output of the 7404 goes LOW. This turns on Q1 a P-channel MOSFET power transistor, turns off Q2 a N-channel MOSFET.

A load such as an LED connected between Y and ground would turn on.

If DIN is LOW The output of the 7404 goes HIGH. Q1 is turned off, Q2 is turned on. This is the "sink" mode. A load such as an LED connected between Y and +5V will turn on.



Sink current demo circuit.
Fig. 3 Sink current demo circuit.

Source current demo circuit.
Fig 4 Source current demo circuit.

High voltage buffer circuit using ULN2003 and pull up resistor.
Fig 5 High voltage buffer circuit using ULN2003 and pull up resistor.

High current TTL driver circuit with motor
Fig. 6

Here I use two identical circuits each connected to one side of a DC motor. Two inputs can forward or reverse the motor rotation. Note the truth table. Only when the inputs A and B differ does the motor operate.

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