What is the function of base drive circuit of a power BJT?

What is the function of base drive circuit of a power BJT?

The circuit is driven from a voltage source which switches between 0 and V volts. The bias current is limited by V and R1+R2, with an initial current surge to charge up the base limited in magnitude by R1 and duration by C. At turnoff the charge in the capacitor C drives the base negative and helps the recovery.

What are the base drive techniques for improving switching speed of BJTs?

Requirements of Base Drive

• A fast rising (< 1 μS) current to turn on the device fast.
• A hard drive of adequate magnitude (IB ) to reduce turn on loss.
• A steady base current of adequate magnitude (IB) to keep the device in saturation during the on period of the switch.

Why is isolation of gate and base drives required?

This allows individual circuits to possess different ground potentials. Signal and/or power can still pass between isolated circuits using inductive, capacitive, or optical methods. For a system with gate drivers, isolation may be necessary for functional purposes and it might also be a safety requirement.

What is power BJT?

Power Bipolar Junction Transistor (BJT) is the first semiconductor device to allow full control over its Turn on and Turn off operations. It simplified the design of a large number of Power Electronic circuits that used forced commutated thyristors at that time and also helped realize a number of new circuits.

What is difference between BJT power BJT?

It is the maximum current carrying capacity which differentiates them. Power BJT has current carrying capacity in Amps where as amplifier type of BJT has less rating than Power varieties. Usually these are used in Power supply type of circuits. These power BJTs have low beta compared its amplifier counterpart.

What is speed-up capacitor?

A SPEED-UP CAPACITOR. In many practical circuits, a shunt reverse bias arrangement is used where the reverse bias voltage is supplied to the base terminal through a large value resistor in shunt with the ‘On’ drive. This arrangement minimizes the transient current passing through the biasing network and biasing battery …

How does a base drive circuit work in a computer?

The following figure shows the simple base drive circuit which may be used to provide a suitable drive. The circuit is driven from a voltage source which switches between 0 and V volts. The bias current is limited by V and R1+R2, with an initial current surge to charge up the base limited in magnitude by R1 and duration by C.

Why is BJT important in base drive circuit?

Following are the important points about BJT to be remembered when designing the base drive circuit for the transistor. BJT is a current controlled device. Its operation is controlled by the base current. The Power BJT is used as ON/OFF switch in the power converter circuits.

Why do you need a base drive for a power transistor?

Click here to know about the Basics of Power Transistor. A Power BJT switching a large current needs a base drive current sufficient to keep the transistor turned ON. The current gain may be quite low, so the base drive may will be 10% of the load current.

How does the bias of a base drive work?

The bias current is limited by V and R1+R2, with an initial current surge to charge up the base limited in magnitude by R1 and duration by C. At turnoff the charge in the capacitor C drives the base negative and helps the recovery. Saturation of the device should be avoided to ensure the fast switching.