Pulse Width (PWM) Controller Circuit

A LM3900 quad operational amplifier can be used to build a pulse width (PWM) controller. The LM3900 was chosen because it only need single supply voltage of 4 to 30 V. This circuit can give 100 percent pulse-width control.  A1 op-amp forms a 1 kHz oscillator, generating a square wave oscillator for the basic oscillation. A2 is a ramp generator […]

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Separate ON-OFF Touch Switch

Providing a touch switch can be a cool way to make your circuit looks sophisticated. Moreover, providing separate touch pad for “on” and “off” function improve the safety, since touching one function doesn’t trigger opposite action to what we expect even at wrong assumption about current state. Here is the schematic diagram of the circuit: How this circuit works is […]

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Remote On-Off Switch through Small Transformer

This is a remote on-off switch circuit. With this circuit, we can take the benefit of using small switch to control larger AC current from high power devices. Safer operation is the other benefit, since this circuit is control the power without running line-voltage switch leads, only low voltage exposure for human operator. Here is the  schematic diagram of the […]

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