Resistance and grid resistance in the hottest sinu

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What is the role of resistance and grid resistance in sinusoidal AC circuit

the relationship between the voltage at both ends of the resistive element and the current passing through it is constrained by Ohm's law. When the sinusoidal current flows through the resistance R, as shown in the figure, the selected voltage is consistent with the reference direction of the current, then according to Ohm's Law:

if the current I is selected as the reference sinusoidal quantity, then

is substituted into the above formula:

the waveform of current and voltage is shown in the figure. It can be seen from the above that when the current flowing through the

resistance is a sinusoidal function, the voltage on the resistance is a sinusoidal quantity with the same frequency as the current. Current and voltage are in the same phase, and their effective values also obey Ohm's law, that is:

if expressed in phasor form, there is

the above formula is a complex form of Ohm's law expression. This formula also expresses the phase relationship and effective value relationship between sinusoidal voltage and current on the resistance element. According to the formula, the phasor diagram of voltage and current can be drawn. Because most mechanical parts work under cyclic load, fatigue failure becomes the main gear of mechanical parts. There is oil stain, dirt on the toothed rod or the upper limit plate of the toothed rod is pressed too tightly, as shown in the figure

selection rules and working principle of grid resistance in IGBT circuit

I. The role of grid resistance Rg

1. Eliminate grid oscillation

the capacitive structure between the grid emitter (or grid source) of insulated grid devices (IGBT, MOSFET), and the parasitic inductance of the grid circuit is inevitable. If there is no grid resistance, the grid circuit will produce strong oscillation under the excitation of the driver driving pulse, Therefore, a resistor must be connected in series to attenuate rapidly

2. Power loss of transfer driver

capacitors and inductors are reactive components. If there is no grid resistance, most of the driving power will be consumed on the output tube inside the driver, making its temperature rise a lot

3. Adjust the on-off speed of the power switching device

the grid resistance is small, the switching device is fast on-off, and the switching loss is small; On the contrary, it is slow and the switching loss is large. However, if the driving speed is too fast, the voltage and current change rate of the switching device will be greatly increased, resulting in greater interference, which will seriously make the whole device unable to work, so we must take overall consideration

II. Selection of grid resistance

1. Determination of grid resistance value

under various considerations, the selection of grid resistance will be very different. The initial test can be selected as follows:

IGBT modules of different brands may have their own specific requirements, which can be debugged near the recommended values in their parameter manuals

2. Determination of grid resistance power

the power of grid resistance is determined by the power of IGBT grid drive. Generally speaking, the total power of grid resistance should be at least twice the grid drive power

igbt grid driving power P = f Ma Zhanfeng, Secretary General of China Plastics Processing Industry Association, attended the meeting and delivered a speech UQ on behalf of Qian Guijing, President of China Plastics Processing Industry Association, and Cao Jian, executive vice president of China Plastics Processing Industry Association, where:

F is the working frequency

u is the peak value of the driving output voltage

q is the gate charge, which can be referred to the IGBT module parameter manual

for example, a common IGBT Driver (such as TX can control the vertical and horizontal offset and change ka101 of the pier) outputs a positive voltage of 15V and a negative voltage of -9v, then u=24v,

assuming f=10khz, q=2.8uc

P> can calculate p=0.67w, and the grid resistance should choose 2W resistance, or two 1W resistors in parallel

III. other precautions for setting the grid resistance

1. Try to reduce the inductive impedance of the grid circuit. The specific measures are:

a) the driver is close to the IGBT to reduce the lead length

b) the gate emitter leads of the drive are twisted, and do not use too thick wires

c) the distance between the two driving lines on the circuit board shall be as close as possible

d) non inductive resistance is used for grid resistance

e) if it is an inductive resistance, several can be connected in parallel to reduce the inductance

2. IGBT on and off select different gate resistors

usually in order to achieve better driving effect, IGBT on and off can adopt different driving speeds, and it is often necessary to select rgon and rgoff (also known as rg+ and rg-) respectively

some IGBT drivers are controlled by turning on and off respectively, such as Lok Muk Yuen tx-ka101, tx-ka102, etc., as long as rgon and rgoff are connected respectively

some drivers only have one output terminal, such as luomuyuan tx-k841l and tx-ka962f, which requires a series connection of resistor and diode in parallel on the original RG to adjust the driving speed in two directions

3. Rge = 10-100k resistance on the gate emitter of IGBT indirectly, so as to prevent accidental application of main power high voltage and burning of IGBT through Miller capacitor when the driving lead is not connected. There is already rge on the common models of luomuyuan drive board (such as tx-da962dx, tx-da102dx), but considering the above factors, users had better add rge between the gate emitter of IGBT or the gate source of MOSFET

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