1. Schematic diagram

1.1 Main control chip and its peripherals

Using an external switch tube solution can easily obtain greater current or power. LM25116 is a synchronous buck controller from National Semiconductor. It adopts current control mode and supports up to 40V input. For peripheral circuits, just use the calculations recommended in the manual. The switching frequency is 250K; the MOS tube model uses NCE0110K with a voltage resistance of 10V; the feedback resistor uses a 10k and a 1k series connection to achieve coarse adjustment and fine adjustment; for convenience, the input is configured with two sockets, KF and DC005.

1.2 Overcurrent protection circuit

Overcurrent protection is a very practical function. The idea of ​​the overcurrent protection circuit is to use a comparator to compare the amplified current signals. The reverse terminal of the comparator is connected to the set voltage, and the non-phase terminal is connected to the current signal. In this way, when the current signal is greater than the set value, the comparator will output a high level, and after passing through a small power MOS tube AO3400, the relay will be driven to disconnect the output, and at the same time, a warning will be issued. The lights come on.

According to the requirements, the overcurrent protection needs to implement the logic of "automatic triggering and manual reset", and the RS latch is used to realize this function. Once the protection is triggered, the relay will remain open until the reset button is pressed. This project uses two NOR gates to form an RS latch. In order to avoid the randomness of the latch state when powering on, R18 and C18 form a charging circuit to initially reset the latch within a short period of time after powering on.

1.3 Auxiliary power supply

To power the low-voltage chip, the Xinlong 1509-5.0 with higher voltage resistance was selected.

1.4 Voltage and current display

A finished three-digit voltmeter module is used, which is not shown in the schematic diagram. Leave mounting holes on the PCB, and then solder the leads directly to the location to be measured. Since the current signal passes through the 20mR alloy resistor and then passes through the 50 times method, it is exactly 1V/1A. The current value can be read directly by connecting it to the voltmeter.

2. Layout

3.Finished product