Summary of 5V to 12V Step Up DC-DC Converter
This article details a 5V to 12V step-up DC-DC converter project utilizing the LM2577-ADJ IC. The circuit delivers an 800mA output load with internal features like a 52 kHz oscillator, soft-start, and current-mode control. It requires minimal external components, using specific resistors to adjust the feedback voltage for flexible output settings based on the formula Vout = 1.23V(1+R2/R3).
Parts used in the 5V to 12V Step Up DC-DC Converter:
- LM2577-ADJ IC
- Inductor L1
- Diode
- Output Capacitor
- Feedback Resistor R2
- Feedback Resistor R3
Step up DC-DC converter is based on LM2577-ADJ IC, this project provides 12V output using 5V input, maximum output load 800mA. The LM2577 are monolithic integrated circuits that provide all of the power and control functions for step-up (boost), fly back, and forward converter switching regulators. The device is available in three different output voltage versions: 12V, 15V, and adjustable.
Requiring a minimum number of external components, these regulators are cost effective, and simple to use. Listed in this data sheet are a family of standard inductors and fly back transformers designed to work with these switching regulators. Included on the chip is a 3.0A NPN switch and its associated protection circuitry, consisting of current and thermal limiting, and under voltage lockout. Other features include a 52 kHz fixed-frequency oscillator that requires no external components, a soft start mode to reduce in-rush current during start-up, and current mode control for improved rejection of input voltage and output load transients.
Features
- Requires Few External Components
- Input 5V DC
- Output 12V DC
- Output Load 800mA
- Current-mode Operation for Improved Transient Response, Line Regulation, and Current Limit
- 52 kHz Internal Oscillator
- Soft-start Function Reduces In-rush Current During Start-up
- Output Switch Protected by Current Limit, Under-voltage Lockout, and Thermal Shutdown
Project is based on LM2577-ADJ IC for flexibility to obtain other output voltages by changing value of feedback resistors R2 and R3
Output Voltage Formula V Out=1.23V (1+R2/R3) (Read Data Sheet for more information about Inductor value, Capacitor, Feedback resistors, Output current and voltage)
LM2577 turns its output on and off at a frequency of 52 KHz, and this creates energy in the inductor L1.
When the NPN switch turns on, the inductor current charges up at a rate of vin/L1, storing current in the inductor. When the switch turns off,, the lower end of the inductor flies above Vin, discharging its current through diode into the output capacitor at rate of (Vout-Vin)/L1. Thus energy stored in the
inductor during the switch on time is transferred to the output during the switch off time. The output voltage is controlled by amount of energy transferred which , in turn, is controlled by modulating the peak inductor current. This is done by feeding back portion of the output voltage to the error amp, which amplifies the difference between the feedback voltage and a 1.23V reference. The error amp output voltage is compared to a voltage proportional to the switch current ( ie., inductor current during the switch on time)
For more detail: 5V to 12V Step Up DC-DC Converter
- What is the maximum output load of this converter?
The maximum output load is 800mA. - How can the output voltage be adjusted?
The output voltage is adjusted by changing the value of feedback resistors R2 and R3. - Does the LM2577 require an external oscillator?
No, it includes a 52 kHz fixed-frequency oscillator that requires no external components. - What protection features are included on the chip?
The chip includes current limiting, thermal shutdown, and under-voltage lockout. - How does the inductor store energy in this circuit?
The inductor stores energy when the NPN switch turns on and transfers it to the output when the switch turns off. - What is the reference voltage used for error amplification?
The error amp compares the feedback voltage against a 1.23V reference. - Can this regulator be used for fly back converters?
Yes, the LM2577 provides power functions for step-up, fly back, and forward converter switching regulators. - What function does the soft-start mode serve?
The soft-start mode reduces in-rush current during start-up.
