SG - Voltage Mode PWM, SGAN, SGAPTR, SGAP, STMicroelectronics. The smart way to design your application. Watch the video . Activating this circuit by applying a positive OSCILLATOR SECTION (Note 5, unless otherwise noted.) Input Threshold, Maximum Duty Cycle (Note 5). Vth. − . Jan 11, The Application of SG Pulse Width Modulator in Intermediate. Frequency Induction Heating Power Supply. Xiao-ping Zong,Teng-yue Ma.
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Activating this circuit by applying a positive OSCILLATOR SECTION (Note 6, unless otherwise noted.) Input Threshold, Maximum Duty Cycle (Note 6). Vth. – . Activating this circuit by applying a positive signal on the shutdown pin NOTE. Information in the following applications sections is not part of the TI component. Part Number: Application Note Power Supply And Power Management SG AN, Maunfacturer: ST Microelectronics, Part Family: Ap, File type: PDF.
The internet isn't much help either. Tahmid's blog has a pin-by-pin functional description with a demonstration circuit, and the SGx App Note describes a related chip, but with important differences. If you don't understand something here, take a look at Tahmid's blog for a counterpoint explanation.
The output will be high when the triangle is higher than the reference and low everywhere else. Adjusting the reference adjusts the pulse width.
The UC chip is basically a triangle wave generator and comparator, with some extras thrown in for convenience. Any properly-scaled voltage proportional to output error can be used as a reference voltage to the comparator.
A larger error results in a higher reference voltage, which clips the triangle wave higher, which makes the output pulses narrower, which generates less output, which in turn generates a lower error voltage. For example, a 12V power supply might have an error voltage proportional to the difference between 12 volts and the actual output. The voltage will shorten or lengthen the PWM times, forcing the output to exactly 12 volts.
The circuit doesn't have to be a power supply, it only needs a feedback voltage proportional to the error. To run a DC motor at a specific speed, simply feed back a voltage proportional to the difference between the requested speed and the actual speed: negative feedback will force the motor to the right speed.
So for another example, you can make a class-D amplifier using an audio signal as Vref: Precision voltage source The UC supplies a precision 5. For other circuits, simply generate 5.
An example from Tahmid's blog : Error Amplifier The UC implements an extra op-amp on the VRef input of the comparator and brings the connections out to the user. This makes it easy to convert error signals - the positive input can level shift, while the inverting input and feedback can amplify the error to bring it into range.
You can also use the op-amp to slow down the feedback. In the circuit below, the PWM error adjustment is delayed by the RC constant of the amplifier feedback. This can eliminate ringing and spurious oscillations that you might get from instantaneous feedback. The control circuit is then isolated from the output.
Triangle wave oscillator So a natural question to ask is: how does one generate a triangle wave? You start with a constant current source. Pins 11 and 14 are the outputs from which the drive signals are to be taken. They have a continuous current rating of mA and a peak rating of mA. When greater current or better drive is required, a further driver stage using discrete transistors or a dedicated driver stage should be used.
Similarly a driver stage should be used when driving the device causing excessive power dissipation and heating of SG When driving MOSFETs in a bridge configuration, high-low side drivers or gate-drive transformers must be used as the SG is designed only for low-side drive. Pin 10 is shutdown. When this pin is low, PWM is enabled. When this pin is high, the PWM latch is immediately set. This provides the fastest turn-off signal to the outputs. An alternative method of shutting down the SG is to pull either pin 8 or pin 9 low.
However, this is not as quick as using the shutdown pin. So, when quick shutdown is required, a high signal must be applied to pin This pin should not be left floating as it could pick up noise and cause problems.
So, this pin is usually held low with a pull-down resistor. Pin 9 is compensation. It may be used in conjunction with pin 1 to provide feedback compensation.
You can firstly see that the supply voltage has been provided and ground has been connected. The decoupling capacitor 0. You should always use this in all your designs. Do not omit the bulk capacitor either, although you may use a smaller value. Following figure shows the pin number along with their pin names. Each pin is allocated with different function. Following figure shows the pin number, pin name and functions associated with each pin. There is another way of turning off the output which involves the shutdown circuitry of pin 10 that comes with an added amount of shutdown options.
This circuit is activated by providing positive signal at the pin 10 which then executes two functions i. If the shutdown command is applied for short period of time, the PWM signal will be eliminated without discharging soft-start capacitor significantly, helps in carrying out pulse by pulse current limiting. However, if pin 10 is hold for longer duration will discharge the external capacitor quickly.