How to adjust the output voltage of MC34063A

Adjusting the output voltage of MC34063A can be done through the following steps:

1、 Understand the basic principles
The output voltage regulation of MC34063A mainly relies on its internal negative feedback mechanism. The chip has an external feedback resistor and voltage divider resistor network to detect changes in output voltage and stabilize the output voltage by adjusting the conduction time of the switching transistor. When the output voltage deviates from the set value, the feedback circuit will make corresponding adjustments.

2、 Specific adjustment methods
Voltage regulation through pin 2:
Pin 2 of MC34063A is the feedback input terminal. When the voltage of pin 2 is higher than the internal reference voltage (1.25V), the output voltage will decrease; On the contrary, when the voltage of pin 2 is lower than 1.25V, the output voltage will increase.
Therefore, the voltage of pin 2 can be adjusted by changing the circuit connected to pin 2, such as resistors, capacitors, etc., in order to regulate the output voltage.
Adjust through an external resistor voltage divider network:
The external resistor voltage divider network is connected between pin 5 (comparator input) and pin 6 (reference voltage input).
By changing the value of the resistor in this voltage divider network, the voltage fed back to pin 5 can be altered, thereby changing the output voltage.
Specifically, increasing the value of the voltage divider resistor will increase the feedback voltage, resulting in an increase in the output voltage; Reducing the value of the voltage divider resistor will decrease the feedback voltage, resulting in a decrease in the output voltage.
3、 Practical operation steps
Determine the required output voltage:
Firstly, clarify the required output voltage value for the circuit.
Calculate resistance value:
Calculate the required resistance value of the external resistor voltage divider network based on the data manual and output voltage calculation formula of MC34063A.
Connecting circuit:
According to the calculation results, connect the corresponding resistors between pin 5 and pin 6, as well as between pin 2 and ground (if necessary).
Testing and adjustment:
After connecting the circuit, power on and test the output voltage. If the output voltage deviates from the desired value, it can be adjusted by fine-tuning the resistance value.
Stability verification:
After the adjustment is completed, stability testing should be conducted to ensure that the output voltage can remain stable under different load and input voltage conditions.
4、 Precautions
Component selection:
High precision and low temperature coefficient resistors and capacitors should be selected to improve the accuracy and stability of the output voltage.
Layout and wiring:
When laying out the PCB, attention should be paid to placing the input and output filtering capacitors as close as possible to the corresponding pins of the MC34063A chip to reduce interference and losses.
Heat dissipation considerations:
MC34063A generates a certain amount of heat during operation, so appropriate heat dissipation measures should be considered to ensure the normal operation of the chip.
Protection mechanism:
The built-in overcurrent protection and thermal protection mechanisms of MC34063A should be fully utilized to improve the reliability and safety of the circuit.
By following the above steps and precautions, the output voltage of MC34063A can be effectively adjusted, ensuring the stability and reliability of the circuit.