Only a few volts of V GS is sufficient to keep the MOSFETs turned fully ON. Consequently, the power latches ON even after the button is released. With the low-side FET ON, the gate of the high-side FET is pulled low, keeping it turned ON. The output voltage rise is transmitted to the N-MOSFET's gate through the 10μF capacitor and resistors, turning it ON. When the MOSFET is OFF, a momentary touch of the ON/OFF button pulls the gate low for tens of milliseconds, fully turning on the high side MOSFET. The 10μF capacitor should be a low leakage variety – a ceramic capacitor works well.Ĭircuit operation is as follows: When power is first applied, the source-gate voltage of the P-FET either remains zero, keeping the high side switch OFF, or the gate is held low as the source rises, turning on the MOSFET, depending on the position of the Auto-ON jumper.
On off button switch download#
As it's quite a versatile device, for your convenience you can view or download the IRF7319 datasheet here: The package includes ultra-low ON resistance N- and P-MOSFETs. The input voltage is limited by the maximum gate-source voltage, V GS, of the MOSFETs, which is 20V – so I recommend a maximum input voltage of 18V, allowing a safety margin of 2V.īoth N-type and P-type MOSFETs are provided in a single SMD package as part number IRF7319 1), making the circuit's total real estate requirement minimal. The R DS-ON of the P-MOSFET used as the high-side switch is only 0.058 ohms so its small surface mount package doesn't heat much, even at currents of 4 amp. For it to reliably turn OFF, the load should draw sufficient current so that any downstream capacitors will discharge within a few seconds, allowing the gate drive of the N-MOSFET to decay. While it is ON, pressing and holding the button for more than 3 seconds turns the power switch back OFF, and it stays OFF until the next momentary button press. When in its OFF state, momentarily pressing the tactile button turns ON the switched power and it latches ON, supplying power to the output. And that power is minimal the P-MOSFET has an ON resistance of only 58 milli-Ω.
On off button switch series#
Even in the ON state the circuit draws very little bias current to maintain its latched state – only the series pass transistor dissipates some power as it passes the load current. In the initial OFF state, this circuit uses no power – the only current drawn is the sub-microamp reverse leakage currents of the diode and the MOSFETs.
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