상세 컨텐츠

본문 제목

Full Bridge Mosfet Driver Circuit

카테고리 없음

by omenliren1987 2020. 2. 18. 11:24

본문

This is entirely possible but you need some way to generate the higher-than-supply gate voltage required by the high-side MOSFET. There are several possible ways of doing this:.Generate this high side voltage from a separate source, using something like a sub-US$0.1 chip like MC34063 connected into a small boost converter. This method works with any drive waveform.Use a gate driver chip like the sub-$1 IR2110. This requires a PWM drive waveform as it generates this high voltage using a bootstrap process (essentially a switched capacitor synchronous charge pump).

  1. Power Mosfet Gate Driver

Driver circuitsA typical digital logic output pin can only supply tens of mA (milliamps) of current. Even though they might require the same voltage levels, small external devices such as high-power LEDs, motors, speakers, light bulbs, buzzers, solenoids, and relays can require hundreds of mA. Larger devices might even need several amps. To control smaller devices that use DC, a transistor-based driver circuit can be used to boost the current to the levels needed for the device. When voltage and current levels are in the correct range, the transistor acts like a high-current switch controlled by the lower current digital logic signal. A discrete is sometimes used instead of a newer transistor especially on older or low voltage circuits as shown below. On mbed, any GPIO pin could be used for the logic control input to the circuit with.Basic driver circuit using a BJT transistorThe transistor primarily provides current gain.

PNP, NPN, or MOS transistors can also be used. The resistor used on the base of the transistor is typically around 1K ohm. On inductive loads (i.e., motors, relays, solenoids), a diode is often connected backwards across the load to suppress the voltage spikes (back EMF) generated when turning devices off. (Recall on an inductor V=L.di/dt, so a negative voltage spike is produced when turning the device off). Sometimes the diode is also connected across the transistor instead of the load (this protects the transistor).

The shown below is a small discrete low-cost BJT transistor that can be used for a driver circuit needing less than 200 mA. In this circuit with BJTs, Vcc can also be a higher voltage DC supply than the logic power supply. 6 or 12V DC is often needed for motors or relays.

In battery operated devices, the load may be directly connected to the battery power and not pass through the voltage regulator. Many devices such as motors have a momentary large inrush current spike when they are first turned on and have a larger stall current, so be a bit conservative on the maximum current ratings.Depending on the current gain of the transistor used, some adjustments may be needed in the value of the base resistor. A high gain TO-92 transistor such as the can drive up to 2A at up to 12V in this circuit. A pair contains two BJT transistors connected together for higher current gain. If a Darlington transistor in a TO-92 package such as a is used in the driver circuit, outputs of 1A at up to 100V are possible. At high current levels, the transistor might get a bit hot.

Transistors can even get too hot and burn out, if the circuit is not designed correctly. The transistor has to dissipate the power (V.I) across its C-E junction (i.e., the switch point) as heat. This means that the transistor should either be completely “on” (saturation) or “off” (cutoff) to minimize heat dissipation and maximize efficiency. Larger power transistors have metal tabs on the case that can be connected to a heat sink for cooling.

The pins on larger power transistors are often too large for standard breadboards and the spacing is not always compatible.PWM ControlThe logic signal (control) turns the transistor on and off to drive high current loads. For motor speed control or dimming lights, a is typically used for control instead of an analog output. Digital PWM is more energy efficient than analog as it significantly reduces the heat dissipated by the transistor (i.e., it is always completely 'on' or 'off'). For motors, the PWM clock rate is typically in the tens of KHz range. For lighting, it needs to be greater than 50Hz or perhaps 100Hz. Early studies for electric power systems showed that many people have headaches caused by lighting systems that use less than 50Hz AC even if they do not directly perceive a flicker.

Power Mosfet Gate Driver

A uses PWM to drive audio speakers and the PWM clock rate is typically around ten times the highest frequency in the audio signal. A is sometimes added on the output. The mbed shows an example using PWM to dim an LED. Even when using PWM, some large transistors may require a for proper cooling. If the transistor gets too hot to touch, it needs a larger heatsink. Floating InputsNote the 10K pull-down resistor on the control input line. This prevents the gate input from floating high and turning on the device when nothing is driving the input.

If it did float, it is also possible that the MOSFET might oscillate and overheat. In most cases, the device should be off if something is wrong. This can happen if a wire was not connected or perhaps briefly when the microcontroller is reset and GPIO pins reset to input mode. It also might happen if the power supply for the microcontroller is not on, but another power supply for the device is on.

A similar design issue of leaving control inputs floating in a computer control system in a hydroelectric power plant once caused a major power blackout in California when power was lost on the computer.Wiring mbedMOSFET PCB5V. Safety Note on High VoltagesA high voltage power line shorted to a digital logic circuit on a breadboard can blow up an entire computer system, or cause electrocution if touched.For safety, keep the wires for any high voltage and/or high current devices well away from the breadboard and do not touch them when power is on.

Mosfet

Even a momentary wire short can blow things ups. An inline fuse and even a breaker is not a bad idea. Long before a standard household AC circuit breaker trips, electronic parts will blow out with a short. Make sure that the bottom side of the PCB does not short out on any metallic surfaces. Breadboard contacts and small jumper wires only handle about one amp. The relay boards typically use screw terminals to attach the larger wires needed for the external device.

Just driving the coil of a large relay requires most of the additional current that can be supplied to mbed via the USB cable, so an external DC power supply will likely be needed to power the relay coils and the load of the external device. For electrical isolation, when using a relay to control external AC devices or high voltage DC devices, do not connect the grounds on the power supplies from the control side to the load side.Here is an example program the turns the relay on and off every 2 seconds.