Make Current Transformer for Switching Power Supply | Half Bridge Protection Circuit Explained

Ajouté : 2026-05-14

[00:00:00]Designing and winding a current transformer is often a challenging task for beginners.

[00:00:05]In this video, I will guide you through the process of calculating and winding a current transformer.

[00:00:11]And this is the result after you finish watching this video.

[00:00:16]When the output current exceeds the preset limit, the circuit will immediately shut down the output pulses and the overload indicator LED will light up.

[00:00:25]The protection current threshold can be easily adjusted using a potentiometer.

[00:00:30]This is an essential circuit for switching power supplies.

[00:00:34]I will guide you through the calculation and winding process of a current transformer after a short introduction to my sponsor and partner, JLCPCB.

[00:00:43]I'd like to thank JLCPCB for supporting this video.

[00:00:48]Over the years, I've used JLCPCB's one-to-four-layer PCB in many projects and they've always been reliable with fast turnaround. Now, JLCPCB is making high-performance six-layer PCB more accessible. With six layers, routing becomes cleaner and more efficient, increasing wiring density by around 30% 50%, so you spend less time dealing with routing limits and more time focusing on your design. With free via-in-pad technology and ENIG finish included, JLCPCB delivers professional-grade six-layer PCB without the professional-grade price.

[00:01:24]If you want to try it yourself, you can get the latest coupon by clicking the link in the description below.

[00:01:32]This is a switching power supply driver circuit and we need to calculate the current transformer in order for the circuit to operate properly.

[00:01:41]This section covers the calculations required to design the current transformer. It includes two functions.

[00:01:47]The first function is used to calculate the output voltage of the current transformer with a fixed burden resistor value. The second function is used to calculate the burden resistor value.

[00:02:02]First, I will calculate the output voltage of the circuit.

[00:02:06]With a desired protection current of 30 amps and a current transformer winding of 70 turns, each burden resistor value will produce a different output voltage.

[00:02:17]With a burden resistor value of 51 ohms, the CT output voltage is 21 volts.

[00:02:23]This value is too high for the protection circuit input, so we need to reduce the burden resistor value.

[00:02:32]With a protection current of 30 amps and a burden resistor value of 5.1 ohms, the CT output voltage is 2 volts, which is a suitable level for the protection circuit.

[00:02:45]After reentering the values, we obtain a burden resistor of 5.1 ohms with a power rating of 1 watt.

[00:02:53]For my project, I will set the protection current to 0.3 amps and use these parameters to wind the current transformer.

[00:03:02]The final result is that the current transformer will be wound with 80 turns and the burden resistor value is 470 ohms.

[00:03:22]This is the toroidal core I used to build the current transformer.

[00:03:26]You can also choose a similar core for your design.

[00:03:29]This is an enameled coated copper wire with a diameter of 0.3 mm used to wind 80 turns around this toroidal core.

[00:03:38]This is the completed current transformer after winding 80 turns of an enameled coated copper wire around the toroidal core.

[00:03:53]We will need several components, such as a control circuit, capacitors, and MOSFET devices to make the circuit operate.

[00:04:00]The topology used here is a half-bridge configuration.

[00:04:05]Note that the MOSFET used here must be rated for at least 400 V, such as the IRF840.

[00:04:16]A simple rectifier and filtering power supply has been completed. We need to check the circuit voltage before installing the other components.

[00:04:26]The voltage across the capacitors should be about half of the rectified voltage, approximately 150 V.

[00:04:45]The MOSFET devices will be connected to the driver circuit as shown here.

[00:04:55]The operating frequency of the circuit is approximately 40 kHz, and this same frequency is applied to each MOSFET input.

[00:05:09]Final power connection steps before operating the circuit.

[00:05:19]An oscilloscope is connected to the output of the switching transformer.

[00:05:24]The load is a 50 W 24 V light bulb.

[00:05:28]When the light bulb is connected to the output, the circuit immediately shuts down because the power exceeds the preset limit.

[00:05:36]We need to readjust the protection threshold by turning the potentiometer counterclockwise.

[00:05:56]>> After adjustment, the circuit is operating normally.

[00:06:01]Thank you for watching until the end of this video.

[00:06:04]If you found this content helpful, please like, share, and subscribe to support the channel.

[00:06:10]Your support helps me create more detailed tutorials like this in the future. See you in the next video.