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<blockquote data-quote="Mykola Kovalov" data-source="post: 739903">I am new to circuit engineering and have a quite specific task - create a delay-on key with a sharp front, low power supply and high current.I created a simple key on a single 2N2222 transistor how as described in the topic <a href="https://electronics.stackexchange.com/q/524550/101063">switch on delay not working (capacitor, transistor)</a>.It works in general, and allows to change delay time, but does not match the requirements for a current&#039;s front. The current increased during capacitor charging. I googled and built another circuit - using three transistors.<img src="https://i.sstatic.net/xFRXFsqi.png" alt="schematic" class="fr-fic fr-dii fr-draggable " style="" /><a href="https://electronics.stackexchange.com/plugins/schematics?image=https%3a%2f%2fi.sstatic.net%2fxFRXFsqi.png">simulate this circuit</a> – Schematic created using <a href="https://www.circuitlab.com/">CircuitLab</a>But, unfortunately, it also does not as expected. Could I use another type/model of transistor and another value resistor?Below are forms of output currents. <a href="https://i.sstatic.net/tCjYcx3y.png"><img src="https://i.sstatic.net/tCjYcx3y.png" alt="Output diagram" class="fr-fic fr-dii fr-draggable " style="" /></a>Could you please help me improve or correct the circuits according next requirements:<ul>
<li data-xf-list-type="ul">power supply - 3.7 V</li>
<li data-xf-list-type="ul">output current - 400...500 mA</li>
<li data-xf-list-type="ul">sharp front of output current</li>
<li data-xf-list-type="ul">delay time - 4...8 s</li>
<li data-xf-list-type="ul">adjustable delay (by changing capacitor&#039;s value)</li>
</ul></blockquote>

[QUOTE="Mykola Kovalov, post: 739903"] I am new to circuit engineering and have a quite specific task - create a delay-on key with a sharp front, low power supply and high current. I created a simple key on a single 2N2222 transistor how as described in the topic [URL='https://electronics.stackexchange.com/q/524550/101063']switch on delay not working (capacitor, transistor)[/URL]. It works in general, and allows to change delay time, but does not match the requirements for a current's front. The current increased during capacitor charging. I googled and built another circuit - using three transistors. [IMG alt="schematic"]https://i.sstatic.net/xFRXFsqi.png[/IMG] [URL='https://electronics.stackexchange.com/plugins/schematics?image=https%3a%2f%2fi.sstatic.net%2fxFRXFsqi.png']simulate this circuit[/URL] – Schematic created using [URL='https://www.circuitlab.com/']CircuitLab[/URL] But, unfortunately, it also does not as expected. Could I use another type/model of transistor and another value resistor? Below are forms of output currents. [URL='https://i.sstatic.net/tCjYcx3y.png'][IMG alt="Output diagram"]https://i.sstatic.net/tCjYcx3y.png[/IMG][/URL] Could you please help me improve or correct the circuits according next requirements: [LIST] [*]power supply - 3.7 V [*]output current - 400...500 mA [*]sharp front of output current [*]delay time - 4...8 s [*]adjustable delay (by changing capacitor's value) [/LIST] [/QUOTE]

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