gfoot/powercontrolcircuit6A soft power supply circuit with tunable overcurrent cutoff
Powercontrol is an open-source printed circuit board by gfoot, from the gfoot/powercontrolcircuit repository on GitHub, published under the Unlicense licence. It is a 2-layer board of 50.8 × 38.1 mm with 19 parts on 17 nets, routed with 79 tracks and 27 vias.
It is built around the TL072 and IRF9540NS. Its parts include 8 resistors, 3 transistors, 2 switches, 1 capacitor and 1 IC.
 |  |  |
|---|---|---|
| Assembled on breadboard | Assembled on veroboard | Demo video |
This is a circuit for soft-switching a 5V DC input, with a configurable current limit cutoff, tested from around 10mA up to 1.2A.
This is useful because it protects your power supply, wiring, and components against adverse effects due to things like short circuiting, accidental reversed power polarity, placing components incorrectly or backwards in a circuit, or other component failure.
It's not a boost/buck converter or regulator, just a switch for an existing regulated DC input.
Press SW1 to turn the power on. The LED indicates that power is on. Press SW2 to turn the power off.
Use RV2 and RV3 to tune the range of currents that are selectable. See configuration guide for the tuning procedure.
Once tuned, RV1 selects the current limit. When more than this amount of current is drawn, the circuit automatically powers off.
| Ref | Qty | Spec | Notes |
|---|---|---|---|
| Q1-2 | 2 | IRF9540N | P-channel power MOSFET - ideally low RDS(on) at VGS=-4.25V |
| Q3 | 1 | 2N3904 | NPN BJT transistor |
| R1-5 | 5 | 10K | Resistor |
| R6 | 1 | ~0.1 ohm | Power resistor, 1A continuous current, at least 1W recommended |
| R7-8 | 2 | 47K | Resistor |
| RV1-2 | 2 | 3K | Trim pots |
| RV3 | 1 | 10K | Potentiometer |
| U1 | 1 | LM385 | Operational amplifier |
| C1 | 1 | 10u | Capacitor to prevent accidental power-on (may not be necessary) |
Exact component choices are not critical. With the above components, and 6x1ohm 250mW resistors in parallel for R6, at a continuous 1A load, the resistors get slightly warm to the touch and the MOSFET tabs measure 60C-70C, in open air with no heatsinks or active cooling.
The added output impedance appears to be approximately 0.75 ohms with these components, at a load current of 1A; lower currents lead to lower impedance. Choosing Q1-2 with lower RDS(on) at -4.25V or more will have the greatest effect on impedance.
I'm considering the following:
Other suggestions very welcome!
| Qty | Value | Footprint | References |
|---|---|---|---|
| 2 | 10K | Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P7.62mm_Horizontal | R3, R5 |
| 2 | 10K | Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P5.08mm_Vertical | R1, R4 |
| 2 | 3K | Potentiometer_THT:Potentiometer_Runtron_RM-065_Vertical | RV2, RV3 |
| 2 | IRF9540N | Package_TO_SOT_THT:TO-220-3_Vertical | Q1, Q2 |
| 2 | SW_Push | Button_Switch_THT:SW_PUSH_6mm_H5mm | SW1, SW2 |
| 1 | 10K | Potentiometer_THT:Potentiometer_Vishay_T73YP_Vertical | RV1 |
| 1 | 10K | Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P2.54mm_Vertical | R2 |
| 1 | 10u | Capacitor_THT:CP_Radial_D5.0mm_P2.50mm | C1 |
| 1 | 167m | Resistor_THT:R_Axial_Power_L20.0mm_W6.4mm_P25.40mm | R6 |
| 1 | 2N3904 | Package_TO_SOT_THT:TO-92_Inline_Wide | Q3 |
| 1 | 47K | Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P2.54mm_Vertical | R8 |
| 1 | 47K | Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P7.62mm_Horizontal | R7 |
| 1 | LED | LED_THT:LED_D3.0mm | D1 |
| 1 | TL072 | Package_DIP:DIP-8_W7.62mm | U1 |
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It measures 50.8 × 38.1 mm and has 2 copper layers, 1.6 mm thick.
19 parts, built around the TL072 and IRF9540NS. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.
From the gfoot/powercontrolcircuit repository on GitHub, at the commit this page was made from: the board is hardware/powercontrol.kicad_pcb. PCBKit opens the board in the browser, with nothing to install.
Its repository publishes it under the Unlicense licence: you may reuse it on that licence's terms (keep the author's notice, and for a copyleft licence share your changes alike).
