Mosfet Circuit

The circuit shows the method of `mirror` current sensing a MOSFET. A fully conducting MOSFET is resistive and behaves exactly as a resistor. It therefore you limit the voltage across the MOSFET when it is conducting you automatically limit the current flowing through it. In addition the MOSFET``s on resistance has a positive temperature coefficient so as it warms up, keeping the voltage across it limited will automatically reduce the limited current flowing through it, keeping it within its safe region over a wide range of junction temperatures...

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...

This circuit is intended to indicate the power output level of any audio amplifier. It is simple, portable, and displays three power levels that can be set to any desired value. For a standard HiFi stereo power amplifier like the 25W MosFet Audio Amplifier described in these pages, the power output values suggested are as follows:..

This application note will offer a method to voltage control or amplitude modulate the output current of the AD9850 DDS using an enhancement mode MOSFET to replace the fixed RSET resistor; and a broadband RF transformer to combine the DDS DAC outputs to produce a symmetrical AM modulation envelope. Modulation with reasonable linearity is possible at rates exceeding 50 kHz. The AD9850 DDS output current (20 mA maximum) is normally set with a fixed resistor from the RSET (Pin 12) input to ground. The DAC outputs are unipolar and complementary (180 degrees out of phase) of each other...

Generating complementary clock signals in a Spice simulation is an easy task. However, this task gets much harder if you need to introduce some dead time into the signals. This difficulty is especially true when you`re dealing with a variable-pulse-width-modulated switching cycle. In fact, you need to insert a dead-time interval between the switching of any two power devices in series, such as bridge or half-bridge designs that use MOSFETs and switch-mode power supplies and that implement synchronous rectification...

The two photoresistors are used as eyeballs, the left one is used to turn left,the right is to turn right. The "feather sensor" has finally been worked out and will be used for turning the robot with out getting stuck on a corner. In other words when AI-A-1 turns left and is about to hit something the "feather sensor" touches the object and activats the reverse function. The robot has a circut with a capacitor and a power MOSFET that controlls how long to go in reverse. this circuit is coneceted to the "feather sensor" switch...

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...

You can create a dc/dc regulator with an internal switching MOSFET that inverts 12V to produce an output of 200 mA at ­12V (Figure 1). The IC is a high-efficiency device whose low quiescent current (120 µA maximum) is the product of a CMOS process that limits the absolute-maximum input-to-output voltage to 21V...

The circuit in Figure 1 implements a "reverse" phase control, using only a single CMOS 4001 quad NOR gate. The circuit is known as a reverse phase control because, unlike with common triac or SCR controls, conduction begins at the zero crossing of the ac sine wave. Timing of the turn-off point of the two power MOSFETs then controls the power to the load...

Figure 1 shows a complete circuit for an emergency lamp that operates from a 12V automotive battery. The xenon flash tube requires a 250V-dc anode voltage and a 4-kV trigger pulse. To generate the 250V dc, IC1, a switching regulator controller, and T1, a standard Versa-PAC transformer, operate in the discontinuous-flyback mode. With this configuration, circuit efficiency is typically 75 to 80%. R1 and IC1`s internal-sense-threshold voltage limit the peak primary current to 1.6A. The R2/R3 divider and IC1`s internal 1.25V reference at the VFB Pin determine the maximum-voltage setpoint. To generate the 4-kV trigger pulse, a standard cold-cathode- fluorescent-lamp (CCFL) backlight transformer, T2, operates in the forward mode. IC2, a dual MOSFET driver, functions as a 1-Hz oscillator and a one-shot for the trigger pulse for Q2...

A while ago I got an email asking for the schematic of a circuit to detect cut phone lines. It didn`t take me long to find this circuit in Electronics Now. When the circuit detects that a phone line has been cut, it activates a MOSFET which can be used to drive a relay, motor, etc. It can also be connected to a security system. # The "Load" can be a relay, lamp, motor, etc. The circuit can also be connected to a security system to sound an alarm in case the phone line is cut. If the circuit is connected to a security system or other circuit, both circuits must be electrically isolated from each other using an opto-isolator, relay, etc. This also means that the Cut Phone Line Detector must be powered by a seperate 9V supply...

This circuit speaks for itself. When the phone line is okay, Q1 acts as a short with a very high ohms value via R1, R2, and R3 for a total of about 66 MegOhm so very high. When the phone line is cut (open), it activates the MosFet (Q3) via transistor Q2 to drive the load. Substitutes are fine, none of the components are critical. The `Red` and `Green` wires of a telephone wire are *NOT* the positive and negative. They are the TIP and RING wires. So, don`t get confused why the red telephone wire is connected to ground (Gnd). The `LOAD` can be anything you like. A relay, motor, lamp, tape-recorder, stereo, security system, or whatever. Keep in mind that Phone companies don`t like to have anything `directly` connected to their wires for obvious reasons, so use this circuit at your own risk...