UC3842BNG belongs to the PWM (Pulse Width Modulation) controller family. It is mainly used in the design of switching power supplies and is widely used in power conversion and controllers in switch-mode power supplies.

UC3842BNG has a built-in error amplifier and comparator for comparison with the feedback signal to adjust the output voltage. It also contains an internal reference voltage source to generate a stable reference voltage for use by the comparators.

 

Ⅰ.Specification parameters of UC3842BNG

•Length:10.16mm
•Width:6.6mm
•Height:3.44mm
•Switching frequency:500 kHz
•Duty Cycle-Max:96%
•Input voltage:15 V
•Output current:1 A
•Package/Case:PDIP-8
•Rise time:50 ns
•Fall time:50 ns
•Number of output terminals:1 Output
•Output voltage:4.9V to 5.1V
•Product Category:Switch Controller
•Supply current:17 mA
•Operating power supply voltage:30 V
•Power supply voltage (Max):25 V
•Power supply voltage (Min):12 V
•Control characteristics:frequency control
•Product Category:Switch Controller
•Output type:transistor driver
•Dissipated power (Max):1250 mW
•Topology:Boost, Flyback, Forward

 

Ⅱ.Working principle of UC3842BNG

1.Internal reference voltage: UC3842BNG integrates a reference voltage source, usually 5V. This reference voltage will serve as the internal reference voltage of the controller.

2.Pulse width modulation:

•The error signal will be input into the controller's pulse width modulation (PWM) comparator. This comparator compares the error signal with a triangle wave signal.

•The result of the comparison will produce a PWM signal whose pulse width (duty cycle) depends on the size of the error signal. If the output voltage is lower than the set value, the pulse width increases; otherwise, the pulse width decreases.

3.Feedback control:

•The comparator compares the feedback voltage with the internal reference voltage and generates an error signal.

•An external feedback network compares the output voltage to an internal reference voltage. This feedback network typically includes a voltage-divider resistor network that feeds a portion of the output voltage back to the UC3842BNG's feedback pin.

4.Switch tube control:

•By controlling the on time and off time, the output voltage can be adjusted to achieve stable regulation of the power supply.

•The PWM signal will control the conduction time of the external switch. When the PWM signal is high level, the switch tube is turned on and the electric energy is stored in the inductor; when the PWM signal is low level, the switch tube is turned off and the electric energy is transferred to the output load through the diode.

 

 

Ⅲ.Characteristics of UC3842BNG

•Automatic Feed Forward Compensation

•High Current Totem Pole Output

•Wide voltage range:UC3842BNG is able to operate within a relatively wide input voltage range, making it suitable for a variety of application scenarios.

•Over-temperature protection:UC3842BNG integrates over-temperature protection function to protect the device from damage in high temperature environment.

•Current Mode Operation to 500 kHz

•Low Startup and Operating Current

•Overcurrent protection:UC3842BNG has an overcurrent protection function, which can automatically disconnect the output when the load is abnormal to protect circuit components from damage.

•Flexibility:With flexible PWM control, the output voltage can be accurately adjusted by adjusting the values of external components. This flexibility makes the UC3842BNG suitable for a variety of different design needs.

•Trimmed Oscillator for Precise Frequency Control

•Latching PWM for Cycle−By−Cycle Current Limiting

•Undervoltage Lockout with Hysteresis

 

Ⅳ.Application scenarios of UC3842BNG

1.Battery charger: Since UC3842BNG has PWM control and adjustable output voltage characteristics, it is often used to design battery chargers to achieve effective charging and maintenance of batteries. UC3842BNG also has adjustable output voltage characteristics that can be adjusted according to different battery types and charging needs.

2.LED driver: For LED lighting systems, UC3842BNG can be used to design LED drivers to achieve precise control and dimming functions of LEDs.

3.Switching power supply: UC3842BNG is commonly used in the design of switching power supplies, including offline and direct current-to-direct current (DC-DC) converters. It can be used to design offline power supplies to convert alternating current (AC) power to direct current (DC) power. Such application scenarios usually include televisions, computers, home appliances, etc. UC3842BNG is suitable for designing low-power adapters, such as mobile chargers, chargers for electronic devices, etc.

4.Power tool power supply: In power tools, electric vehicles and other applications requiring high power output, UC3842BNG can be used to design efficient power converters. The PWM control function of UC3842BNG can accurately regulate the output voltage and current of the power supply, thereby achieving efficient power conversion.

5.Inverter: In solar power generation, wind energy conversion and other renewable energy systems, it can achieve efficient DC-AC inversion, and its excellent voltage and current regulation characteristics can ensure the stability and reliability of the inverter. sex.

6.Power adapter: UC3842BNG can be used to design various power adapters, including desktop computer adapters, mobile chargers, etc.

Ⅴ.Maximum Ratings of UC3842BNG

 

Ⅵ.Built-in protection function of UC3842BNG

1.Undervoltage lockout (UVLO):
The undervoltage lockout function is used to monitor the input voltage. When the input voltage is lower than the set threshold, the UC3842BNG enters the lockout state to prevent operation under low voltage conditions.

2.Over current protection (OCP):
The overcurrent protection function monitors the output current and takes action if it exceeds a set threshold. This helps prevent damage in overload situations.

3.Short circuit protection:
The UC3842BNG may have a short circuit protection mechanism to detect short circuit conditions at the output and take appropriate protective measures when a short circuit occurs to prevent damage.

4.Over-temperature protection (OTP):
Over-temperature protection monitors the UC3842BNG temperature. When the temperature exceeds the set threshold, the protection mechanism will be triggered, usually by reducing the switching frequency or reducing the pulse width to reduce power consumption, thereby protecting the chip from overheating damage.

5.Overvoltage protection (OVP):
The overvoltage protection function monitors the output voltage and takes measures when the output voltage exceeds a set threshold to prevent damage to the load.

 

Ⅶ.UC3842BNG common faults and solutions

1.Overcurrent protection triggers

•Inductor and capacitor inspection: Check whether the inductor and capacitor are properly selected. Improper components may cause excessive current fluctuations, triggering overcurrent protection.
•Switch tube and diode inspection: Ensure that the rated power and current of the switch tube and diode meet the design requirements.

2.The output voltage is unstable or abnormal

•Reference voltage check: Check whether the reference voltage of UC3842BNG is set correctly to ensure that the output voltage is within the expected range.
•Feedback network check: Check that the connections and components of the feedback network are correct. Make sure the feedback network correctly compares the output voltage to the reference voltage.

3.Output voltage fluctuation or noise

•Filter network check: Make sure an appropriate filter network is used at the output to reduce noise levels.
•Feedback network optimization: Adjust the feedback network to ensure system stability and small output voltage fluctuations.

4.System startup problems

•Initial condition check: Check the initial conditions to ensure that the input voltage and load are within the allowed range.
•Startup circuit analysis: Analyze the startup circuit, including the startup capacitor and undervoltage lockout function.

5.Over-temperature protection trigger

•Ventilation Check: Ensure there is adequate ventilation around the power circuit to prevent overheating.
•Heat dissipation check: Check the heat dissipation of UC3842BNG to ensure it is within the specified operating temperature range.

Ⅷ. How to configure UC3842BNG to prevent over-current or over-temperature problems?

•Overcurrent protection configuration:

1.Select the over-current protection threshold: In the design of UC3842BNG, the maximum output current can be limited by adjusting the over-current protection (OCP) threshold. This can be achieved by introducing appropriate resistors in the current sensor resistor or feedback network.

2.Adjust the current sensor resistance: In the feedback network, adjust the overcurrent protection threshold by adjusting the current sensor resistance.

3.Appropriate current sensor: Select an appropriate current sensor to ensure that its rated current and characteristics meet the requirements of the system.

•Over-temperature protection configuration:

1.Check the over-temperature protection function: Make sure that the UC3842BNG has the over-temperature protection function. Most switching power supply controllers include over-temperature protection, but you need to make sure it works properly within a specific temperature range.

2.Over-temperature protection threshold: If the UC3842BNG allows configuration of the over-temperature protection threshold, make sure it is set at the appropriate temperature. This can be accomplished by adding a resistor network to the COMP pin.

3.Heat dissipation and ventilation design: Provide sufficient heat dissipation to ensure that UC3842BNG works within a suitable temperature range. Consider using a heat sink and ensure the system is designed with adequate ventilation.

4.Over-temperature protection response time: Check the over-temperature protection response time of UC3842BNG to ensure that when high temperature occurs, UC3842BNG can respond in time and take appropriate protective measures.

 

Frequently Asked Questions

1.Can UC3842BNG provide sufficient stability under high load?
UC3842BNG can provide sufficient stability under high load. Factors that need to be considered include: feedback network design, current sensor selection, over-current protection and over-temperature protection, system stability analysis, heat dissipation design, etc.

2.What precautions should be taken for stability at high loads when using UC3842BNG?
Achieving stability at high loads involves careful design of feedback and compensation networks, selection of appropriate external components, and ensuring adequate heatsinking and ventilation to manage increased power dissipation.

3.What is UC3842BNG?
UC3842BNG is a pulse-width modulation (PWM) controller IC used in switch-mode power supply applications. It is commonly employed for designing various power supplies, including offline and DC-DC converters.