UC3845BN
Current mode PWM controllers for power management in DIP-8 packages
Manufacturer： ['stm', 'rochester', 'onsemi', 'lrc']
series introduction
# Introduction to the UC3845BN Product Series
## 1. Overview
The UC3845BN is a highly versatile and widely used integrated circuit (IC) belonging to the family of current - mode PWM (Pulse - Width Modulation) controllers. It is specifically designed for use in switching power supply applications, offering a comprehensive set of features that make it an ideal choice for engineers and designers looking to develop efficient and reliable power supplies.
## 2. Key Features
### 2.1 Current - Mode Control
One of the most significant features of the UC3845BN is its current - mode control architecture. In current - mode control, the inductor current in the power stage is used as a control variable in addition to the output voltage. This provides several advantages over traditional voltage - mode control. It offers better line regulation, faster transient response, and inherent cycle - by - cycle current limiting. The current - mode control helps in stabilizing the power supply under varying input voltage and load conditions, ensuring consistent performance.
### 2.2 Adjustable Oscillator Frequency
The UC3845BN allows for easy adjustment of the oscillator frequency. The oscillator frequency can be set by an external resistor and capacitor connected to the appropriate pins of the IC. This flexibility enables designers to optimize the power supply design for different applications. For example, in applications where size is a critical factor, a higher oscillator frequency can be chosen to reduce the size of the magnetic components such as inductors and transformers. Conversely, in applications where efficiency is the primary concern, a lower frequency may be selected.
### 2.3 Built - in Error Amplifier
The IC comes with a built - in error amplifier. This amplifier compares the feedback voltage from the output of the power supply with a reference voltage. The output of the error amplifier is then used to control the duty cycle of the PWM signal. The error amplifier helps in maintaining a stable output voltage by adjusting the duty cycle of the switching transistor in response to changes in the load or input voltage.
### 2.4 Soft - Start Function
The UC3845BN incorporates a soft - start feature. During the power - on sequence, the soft - start function gradually ramps up the output voltage of the power supply. This helps in reducing the inrush current and stress on the components, improving the reliability of the power supply. It also prevents overshoot of the output voltage, which could potentially damage the connected load.
### 2.5 Over - Current Protection
Over - current protection is a crucial safety feature in power supply design. The UC3845BN has an over - current protection mechanism that monitors the current flowing through the power stage. If the current exceeds a predefined threshold, the PWM output is shut off, protecting the power supply and the connected load from damage due to excessive current.
## 3. Pin Configuration and Functionality
### 3.1 Pin 1 (COMP)
This is the output pin of the error amplifier. An external compensation network is typically connected to this pin to stabilize the feedback loop of the power supply. The compensation network helps in shaping the frequency response of the error amplifier to ensure stable operation and good transient performance.
### 3.2 Pin 2 (VFB)
The feedback voltage from the output of the power supply is applied to this pin. The error amplifier compares this voltage with the internal reference voltage to generate an error signal that is used to control the duty cycle of the PWM output.
### 3.3 Pin 3 (ISENSE)
The current - sensing input pin. A current - sensing resistor is placed in the power stage, and the voltage across this resistor, which is proportional to the inductor current, is applied to this pin. The UC3845BN uses this current information for current - mode control and over - current protection
Images for reference
8-DIP
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