LD7575PS Manufacturer, Advantages and Disadvantages and Other Details
27 February 2024
Ⅱ. Pins and functions of LD7575PS
Ⅳ. How does LD7575PS achieve stable output voltage?
Ⅵ. What is the performance of LD7575PS in high temperature environment?
Ⅶ. What are the advantages and disadvantages of LD7575PS?
Ⅷ. Typical application circuit of LD7575PS
The LD7575PS is a current mode PWM controller with excellent energy-saving operation. It features a high voltage current source that provides starting current directly from the bulk capacitor and further provides a lossless starting circuit. This article will introduce the LD7575PS from the aspects of manufacturer, advantages, disadvantages and applications, and attach its pin diagram and block diagram.
The LD7575PS is a green mode power PWM with high voltage startup circuit power management chip. The chip internally integrates functional circuits such as driver stage, PWM comparator, DSC oscillator, current detect amplifier, reference voltage source, high voltage current source, RS latch, voltage error amplifier, over voltage protection, over current protection and under voltage lockout (UVLO). It is internally set up with a lossless high-voltage current source, which can eliminate the start-up circuit of an ordinary switching power supply. The chip has few peripheral components, only a few resistors, so it can constitute a low-cost high-performance single-ended flyback switching power supply.
Alternatives and equivalents:
• DAP8A
• GR8876
• LAAF1001
• LD7575
• NP203D6
The chip has a dual row 8-pin package. Its pin functions are shown in the figure below.
Pin 1 (RT): This pin is to program the switching frequency. By connecting a resistor to ground to set the switching frequency.
Pin 2 (COMP): Voltage feedback pin (same as the COMP pin in UC384X). By connecting a photo-coupler to close the control loop and achieve the regulation.
Pin 3 (CS): Current sense pin, connect to sense the MOSFET current
Pin 4 (GND): Ground
Pin 5 (OUT): Gate drive output to drive the external MOSFET
Pin 6 (VCC): Supply voltage pin
Pin 7 (NC): Unconnected pin
Pin 8 (HV): Connect this pin to positive terminal of bulk capacitor to provide the startup current for the controller. When Vcc voltage trips the UVLO(on), this HV loop will be off to save the power loss on the startup circuit.
The LD7575PS is manufactured by Leadtrend. The company is headquartered in Hsinchu's Taoyuan Science Park and has been dedicated to the research, development, production, manufacturing and sales of analog integrated circuits since its inception in 2002. In the field of power management ICs, Leadtrend is especially good at PWM IC development technology. At the same time, Leadtrend keeps up with the development trend of the electronics industry, and works closely with its customers to continuously launch products that meet the market demand. Currently, the power control ICs (AC/DC, DC/DC PWM control) developed by Leadtrend are widely used in home appliances, monitors, flat panels, LCD TVs, network communications, notebook computers, smart phones, LED lighting and other fields.
The output voltage stability of LD7575PS is realized by the adjustment mechanism of its internal error amplifier and feedback circuit. When the output voltage changes, the optocoupler will pass this voltage change accordingly. The error amplifier will compare this changed voltage with the internal preset reference voltage and adjust the error signal according to the comparison result. This adjustment process will directly control the pulse width of the LD7575PS and thus stabilize the output voltage. Specifically, if the output voltage rises, the error amplifier will decrease the pulse width to lower the voltage; conversely, if the output voltage falls, the error amplifier will increase the pulse width to raise the voltage. This adjustment mechanism operates continuously to ensure that the output voltage is stabilized. In addition, the high accuracy and sensitivity of the error amplifier supports the reduction of errors and fluctuations and the improvement of output voltage stability.
The LD7575PS has an operating temperature range of -40°C to 85°C, so it can still operate within its normal operating range in high temperature environments. However, it should be noted that as the ambient temperature increases, the temperature of the chip may also increase accordingly, which may have some impact on the performance of the LD7575PS.
In a high temperature environment, we may need to pay attention to the following points:
1. Load current change: As the temperature rises, the load current may change, and this change may cause the output voltage of LD7575PS to become unstable.
2. Power supply voltage fluctuation: A high temperature environment may have an effect on the stability of the power supply voltage. This may cause the input voltage of the LD7575PS to change, which in turn affects its voltage stabilization performance.
3. Chip cooling: As the ambient temperature rises, the temperature of the LD7575PS chip may rise accordingly. If the temperature of the chip is too high, it may lead to a decline in its performance and even affect its service life. Therefore, in a high-temperature environment, it is recommended to take appropriate heat dissipation measures, such as installing a heat sink or ensuring sufficient air circulation in the environment to ensure the normal operation of the chip and extend its service life.
1. Advantages of LD7575PS
(1) High efficiency: The LD7575PS utilizes switching regulator technology, which typically has a high conversion efficiency, helping to reduce power loss and improve system efficiency.
(2) Multiple package options: The LD7575PS is available in a variety of package options such as SOP-8 and DIP-8 packages for different application scenarios and PCB layout requirements.
(3) Wide operating voltage range: The LD7575PS is able to adapt to a wide range of input voltages, usually between 85V and 265V, and is suitable for a variety of occasions with large fluctuations in input voltage.
(4) High integration: LD7575PS has control circuits, integrated switching tubes, feedback networks and other functions, which makes the overall circuit design simpler and can reduce the number of external components and PCB area.
2. Disadvantages of LD7575PS
(1) Complex design: The design of LD7575PS is relatively complex because it involves more circuit parameters and operating principles, and therefore requires a higher level of skill on the part of the designer.
(2) EMI problem: LD7575PS will generate switching noise and electromagnetic interference (EMI) during operation, so it needs to take corresponding filtering and shielding measures to effectively deal with it.
(3) High requirements for external components: Although the LD7575PS has a high degree of integration, it still requires some external components to complete the regulator circuit, so there are certain requirements for the selection and connection of external components.
1. Protection circuit
(1) Undervoltage protection circuit
LD7575PS itself has UVLO (undervoltage lockout) function. When the voltage of pin ⑥ is lower than 10V, the IC will stop working. Once the voltage at the Vcc terminal exceeds 16V, UVLO will be automatically released, and the IC will automatically start and continue to work. Even when the Vcc terminal voltage is lower than 16V but not lower than 10V, the IC can still operate stably and reliably.
(2) Overcurrent protection circuit
R217 and R216 form an overcurrent protection circuit. R217 is not only used for maximum current detection, but also for peak-peak current detection. When the voltage at the Cs terminal of pin ③ is greater than 0.85V, the IC stops working. At the same time, during normal operation, R217 is used to detect the operating current of each frame of Q201. If the power switch tube does not have overcurrent, but its conduction time is too long, IC201 will still stop working, thereby preventing the power switch tube from being burned due to too long conduction time under abnormal circumstances.
(3) Anti-interference circuit
NF201, NF202, CY201, and CY202 together form an anti-interference circuit to ensure that various clutter from the mains will not invade subsequent circuits due to the presence of these EMI anti-interference components. At the same time, the various multiple harmonics generated by the switching power supply itself will not enter the mains network, thereby avoiding interference with other household appliances. In addition, R201, R202, and R203 form a discharge circuit to release the charge stored by CY201 and CY202 when the power supply is working to prevent accidental electric shock when the power supply is unplugged.
(4) Anti-surge circuit
The function of NTC201 is to prevent the current charging C201 through BD201 from being too large at the moment of power-on, thereby avoiding burning BD201 or the fuse. NTC201 is a negative temperature coefficient resistor, its resistance at room temperature is several ohms. However, when powered on, its resistance quickly drops to zero in a short period of time, effectively suppressing the generation of surge current and thus protecting circuit components from damage.
(5) Overvoltage protection circuit
F201 and VDR201 together form an overvoltage protection circuit. When the mains voltage rises abnormally, VDR201 will be turned on in a very short time, forming a large current, causing fuse F201 to blow out immediately, thus preventing high voltage from entering the subsequent circuit and causing larger area component damage. In addition, ZD201, Q202, Q203, and D202 also form another overvoltage protection circuit, specifically used to prevent secondary output voltage abnormalities. When the feedback circuit fails, the voltage of each secondary output will increase abnormally, and the voltage of N4 output will also increase. Once the voltage reaches the preset protection point, ZD201 will break down and conduct, causing Q202 to start working and pull the negative voltage of D202 from 12V to 0.6V. At this time, the voltage of pin ② of IC201 is about 2.2V when working, and the positive voltage of D202 is 1.6V higher than the negative voltage, causing D202 to turn on. This further pulls the voltage of the second pin of IC201 down to about 1V, causing IC201 to stop working, thereby preventing damage to the driver board or LCD screen caused by excessive secondary voltage.
2. Feedback circuit
The second pin of IC201 serves as the FB feedback input terminal, and its external C204 acts as a slow-start resistor. Since the secondary voltage output is unstable at the moment when the IC is started, the operation of IC202 is also unstable. At this time, the voltage output by pin ② will first charge C204. The charging current of C204 provides enough time for the IC to enter a stable operating state. In addition, the external D202 connected to the second pin of IC201 is used to access the overvoltage protection signal.
3. Start the circuit
When the mains power is connected, the 300V voltage at both ends of C201 will be added to the ⑧pin of IC201 through resistors R233 and R234. This voltage charges the external C206 connected to pin ⑥ through the charging circuit inside IC201. When the voltage of pin ⑥ exceeds 16V, the IC starts to start. Subsequently, N4 generates continuous operating power, and the charging circuit inside IC201 will automatically cut off at this time to achieve the purpose of energy saving and consumption reduction. Resistor R233 mainly plays the role of limiting the current to prevent excessive charging current from damaging the IC at the moment of startup. As a protective resistor, R234 will burn itself out when an abnormality occurs in the circuit and the current is too large, thus preventing further expansion of the fault.
4. Push circuit
The push circuit of this machine is similar to UC3842 and 203D6, but the protection measures designed here are more complete. Among them, R214 is used as the push resistor of the G pole, and the resistance value used here is 510 ohms. As a bleeder diode, D203 is mainly used to bleed the VGS voltage generated during the turn-off period of the power switch tube, thereby accelerating the closing process of the power switch tube. ZD204 is used to clamp the vGS voltage to prevent the LD7575 output push voltage from being too high, thereby preventing the power switch tube from being on for too long due to over-excitation. Finally, R215 is a pull-down resistor, which pulls the voltage of the G electrode to a low level during the cut-off period of Q210, thereby preventing conduction due to unexpected interference and thereby protecting the power tube from damage.
5. Peak elimination circuit
R209, R210, R211, R212, C202, and D204 together form a peak-clipping circuit, whose structure is the same as the peak-clipping circuit of the primary coil of a normal switching power supply. R209, R210, R211, and R212 are connected in two series and then in parallel, mainly because these four resistors use chip capacitors, and their power is relatively small. By paralleling two series, the resistance of the resistor remains unchanged at 47kΩ, but the power increases to 2W, thus meeting the needs of the circuit. This kind of circuit is very common in liquid crystal displays, and the peak-cutting protection circuit and overcurrent detection resistor of the secondary rectifier diode often use similar structures. This is mainly to meet process requirements and avoid purchasing additional cylindrical resistors, so that it can be completed in one mechanical patching operation.
6. Power supply circuit
Feedback winding N4, R213, D201, and C206 together form the power supply circuit of IC201 to meet the power supply requirements for continuous and stable operation of the IC after startup. If there is a fault in the starting circuit, a short circuit in the secondary load, or a problem in the feedback circuit, the voltage at the vCC terminal may continue to jump. This is caused by repeated starts, which means that the switching power supply cannot work stably and continuously. Each time it is started, the voltage of C206 is reduced due to the consumption of the IC starting up. If T201 does not start working, the N4 winding will not send pulses and cannot provide continuous charging current for C206, resulting in a voltage drop. At this time, we need to wait for the 30QV voltage to charge C206 through the inside of the IC in order to start again. The operating voltage range of the VCC terminal is usually between 11V and 25V, and the filter capacitor size of the VCC terminal is usually between 10uF and 47uF.
Frequently Asked Questions
1. What is PWM control?
PWM (Pulse Width Modulation) is used to control electric power inside the motor coil. The output power is controlled by repeatedly turning the output ON and OFF.
2. Can LD7575PS handle high input voltages?
Yes, LD7575PS is designed to handle high input voltages, making it suitable for various power supply applications.
3. What are the key features of LD7575PS?
Some key features of LD7575PS include high voltage startup, built-in leading-edge blanking (LEB), optimized line compensation, low standby power consumption, and a wide operating voltage range.
