Circuit - MOSFET Circuits / Schematics List - Circuits designed by David A. Johnson, P.E.

MOSFET Circuits

Circuits designed by David Johnson, P.E.
Last Updated on: Wednesday, April 28, 2010 03:53 PM

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Charge Coupled MOSFET Relay
This circuit acts as an AC/DC relay with a rating up to 50 volts peak and up to 10 amps of current. The differential oscillator supplies voltage to the gates of the two FETs with good isolation will drawing only 1.5ma of current.

CHARGE COUPLED BI-DIRECTIONAL POWER MOSFET RELAY
The circuit uses an inexpensive C-MOS inverter package and a few small capacitors to drive two power MOS transistors from a 12v to 15v supply. Since the coupling capacitor values used to drive the FETs are small, the leakage current from the power line into the control circuit is a tiny 4uA. Only about 1.5mA of DC is needed to turn on and off 400 watts of AC or DC power to a load.

Circuit Protects from Battery Polarity Reversal
This simple circuit can protect a sensitive electronic circuit from an accidental connection of a battery with a reversed polarity. The N-channel FET connects the electronic device to the battery only when the polarity is correct. The circuit shown was designed for a device powered from a single 1.5 volts button cell battery. However, the circuit will operate with higher voltages as well.

FINGER TOUCH ACTIVATED SWITCH
It does not get any easier if you want a solid-state switch that is activated by the touch of a finger. Two small metal pins route voltage through the finger skin to a MOSFET switch. The circuit is great for situations where a membrane type mechanical switch is not desired.

VERY LOW POWER ASTABLE MULTIVIBRATOR
This classic circuit draws only 200 nanoamps from a 1.5v supply.

300V PEAK TO PEAK SIGNAL GENERATOR
This circuit converts a square wave signal to a +-150 volt output signal with fast 100nS rise and fall times.

N-CH AND P-CH TRANSISTORS FORM PUSH-PULL DRIVER
This circuit can produce high speed output signals with fast rise and full times. The unique change pump action allows the voltage of the upper P-ch device to range from millivolts to hundreds of volts. The output current is only limited by the rating of the transistors. I have used this circuit beyond 2MHz.

FET INPUT HIGH SPEED LIGHT DETECTOR
This circuit is yet another design that converts current from a PIN photo diode to a voltage. It has a bandwidth that extends beyond 50MHz.

CHARGE PUMP EFFICIENTLY DIVIDES SUPPLY VOLTAGE
This circuit uses a few FETs and logic devices to down convert a DC voltage to about one half its value.

CIRCUIT PROTECTS FROM BATTERY POLARITY REVERSAL
This simple circuit can protect a sensitive electronic circuit from an accidental connection of a battery with a reversed polarity. The N-channel FET connects the electronic device to the battery only when the polarity is correct. The circuit shown was designed for a device powered from a single 1.5 volts button cell battery. However, the circuit will operate with higher voltages as well.

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