Caution
This project was initiated in 2021 when my skills were more limited. As a result, there might be areas for improvement. I occasionally enhance both the performance and readability of project files for better understanding.
Linear power supply capable of delivering up to 250W (0-28V, 0.01-10A).
- Adjustable voltage and current limit, controlled by 10-turn potentiometers.
- On/off switch for convenient power output control.
- Relay transformer-tab switching circuit for minimizing power losses by reducing the voltage differential across the linear regulator.
- Temperature-controlled fan.
Important
The Q1 transistor was changed from an IRF9530 (P-MOSFET) to a BD912 (PNP-BJT). This significantly improved the power supply's stability and eliminated oscillations in the constant current mode. Their pinouts are compatible, making it a drop-in replacement.
Click for simulation details
Simulations in LTspice demonstrated a significant improvement in the output step response after replacing the Q1 MOSFET with a BJT:
Before (with MOSFET):
After (with BJT):
(The Bode plot also showed better characteristics with the BJT)
For detailed output voltage waveforms before the Q1 transistor was changed to a BJT, please see the measurements.pdf file.
A 12V, 300VA transformer was modified for this project. The secondary winding, originally consisting of 4 parallel wires, was reconfigured. These wires were split into two sets and connected in series to achieve 24V with a center tap. An additional winding of approximately 8V was also added.
An old graphics card heatsink is used for cooling the series pass power transistors.
The design was initially based on the SN1534 power supply. Schematics and further details related to the original design can be found here.