Its internal circuit diagram is as follows:
SG3525 * * * is the 16 pin. Let's explain it in sequence:
Pins 1 and 1. As can be seen from the internal circuit diagram, the 1 pin is the inverting input of the internal error amplifier. The nominal open-loop gain of the internal error amplifier is 80db, and the closed-loop gain is mainly determined by the feedback network. Generally, the 1 pin is mainly connected with the sampling voltage signal to form negative feedback, so that the duty cycle of PWM can be modulated.
Pins 2 and 2 are noninverting inputs of the internal error amplifier. Generally, this pin needs to be connected to a reference source, which can be obtained by dividing the voltage from the pin 16, or it can be connected to a more stable external reference source separately, generally 2.5V Of course, you can also connect a 2V one.
3, 3 pins for external synchronization. When multiple chips need to work synchronously, each chip has its own oscillation frequency, and its four pins and three pins can be connected separately. At this time, the working frequencies of all chips are synchronized with the fastest chip working frequency. It is also possible to make a single chip work at an external clock frequency.
4, 4 pins, synchronous pulse output. Used when multiple chips work synchronously. However, the working frequencies of several chips should not be too different, and the synchronous pulse frequency should be lower than the oscillation frequency. If multiple chips do not need to work synchronously, pins 3 and 4 are suspended. The 4-pin output frequency is twice the output pulse frequency. The output sawtooth voltage range is 0. 6V to 3 v. 5V。
5, 5 pins, CT (oscillating capacitor end). One end of the oscillating capacitor is connected to pin 5, and the other end is directly grounded. Its value range is 0.00 1u F to 0. 1μf。 During normal operation, the sawtooth wave changes from 0.6V to 3. 5V can be obtained at both ends of CT.
6,6 pins, RT (oscillating resistor terminal). One end of the oscillating resistor is connected to pin 6, and the other end is directly grounded. The resistance of RT determines the internal constant current value of CT charging. Its value ranges from 2K ohms to 150K ohms. The larger the RT and CT, the longer the charging time, and vice versa.
7, 7 pins, discharge: the discharge of CT is determined by the dead-time resistance of 5. Seven stitches. Separating the charging and discharging circuits is beneficial to adjust the dead time through the dead resistance, which makes the adjustment range of the dead time wider. Its value range is 0 to 500. The larger the discharge resistances RD and CT, the longer the discharge time and the shorter the discharge time.
8, 8 pins, soft starter. The inverting terminal of the comparator, namely the soft starter control pin 8, can be externally connected with a soft starter capacitor, which is charged by the 50uA constant current source of the internal Vf.
9, 9 pins, compensation (compensation terminal). PI regulator is composed of pin 9 at the output end of the error amplifier and the indirect resistor and capacitor at pin 1 at the inverting input end of the error amplifier, which is used to compensate the amplitude-frequency and phase-frequency response characteristics of the system. The working voltage range of the compensation terminal is 1. 5V to 5.2v v.
10, 10 pin, turn off. As the input terminal of PWM latch, the overcurrent detection signal is generally connected to the terminal 10. When the overcurrent detection signal is held for a long time, the capacitor C 1 connected to the soft start terminal 8 will be discharged. When the circuit works normally, the terminal is at a high level, and its potential is higher than the peak potential of sawtooth wave (3. 30. When the circuit is abnormal, as long as the voltage at the 10 pin is greater than 0. 7V, the triode will be turned on, and the voltage at the inverting terminal will be lower than the valley voltage (0.9V) of the sawtooth wave, so that the output PWM signal will be turned off and play a protective role.
1 1, 1 1 pin, PWM output terminal and 14 pin form complementary PWM signals with a phase difference of 180. Using push-pull output circuit, the turn-off speed is faster when driving the field effect transistor, and the peak value of pull current and sink current reaches 200mA. There is overlapping conduction between output and absorption due to the lag of opening and closing. There is a sharp current pulse at the overlap, which lasts about l00ns. You can find it in v.
The chip's reference ground 12 and 12 pins together with VCC constitute the chip's power supply system.
Pin 13, pin 13, pin 1 1, pin 14 push-pull output the power supply voltage of the upper tube collector, which is connected to VCC. It can also be supplied independently, but the power supply is required to be connected to VCC * *.
Pins 16 and 16, and the internal reference voltage output of the chip is 5V.