12V Transformerless Power Supply

Here the low power 12V transformerless power supply circuit with full-wave rectification. A lot of circuits could be powered straightaway in the electric mains using the support of a series capacitor (C1). The problem with this method is the fact that typically only one half cycle of the mains wave-form can be used to deliver a DC voltage. An obvious option is to work with a bridge rectifier to accomplish full-wave rectification, which improves the amount of current that can be delivered and makes it possible for the filter capacitor to become smaller sized. The associated circuit in fact does this, but in a clever manner that makes use of fewer parts. Right here we take benefit of the reality that a Zener diode can also be a standard diode that conducts electric current in the forward direction. During one half wave, the current flows via D1 through the load and back via D4, whilst during the other half wave it flows via D3 and D2. Keep in mind that with this circuit (and with the bridge rectifier version), the zero voltage reference of the DC voltage is not directly connected towards the neutral line of the 230V circuit.

This means that it is mostly not possible to work with this kind of supply to drive a TRIAC, that normally requires such a connection. Even so, circuits that utilize relays can benefit from full-wave rectification. The value of the supply voltage depends on the specifications of the Zener diodes which are applied, which can be freely selected. C2 have to be able to deal with at least this voltage. The level of current which can be supplied will depend on the capacitance of C1. With the given value of 220nF, the current is about 15mA. A final warning: this kind of circuit is directly connected to mains voltage, which can be lethal. You must certainly not come in get in touch with with this circuit directly without safety equipment! It is critical to mount this circuit safely and securely inside a appropriate case.

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LM317T Voltage Regulator Circuit with Pass Transistor

This is the schematic diagram of voltage regulator circuit with pass transostor. The regulator is based regulator IC of LM317T. The LM317T output current can be raised by utilizing an additional power transistor (on circuit, it is 2N2955) to share a portion of the total current. The amount of current sharing is established with a resistor placed in series with the LM317 input and a resistor placed in series with the emitter of the pass transistor. In the above scheme design , the pass transistor will start conducting when the LM317 current reaches about 1 ampere, due to the voltage drop across the 0.7 ohm resistor. Current limiting happens at about 2 amperes for the LM317 which will drop about 1.4 volts across the 0.7 ohm resistor and make a 700 millivolt drop across the 0.3 ohm emitter resistor. Thus the total current is limited to about 2+ (.7/.3) = 4.3 amperes.

Sealed Lead Acid (SLA) 12V Battery Charger with Current Limiting

This is the circuit design of Smart Sealed Lead Acid (SLA) 12V Battery Charger featuretwith Current Limiting. The charger uses a two step process for charging SLA batteries – a current limited ‘fast’ mode followed by a constant voltage ‘float’ mode. Maximum charging current is 1A. An onboard LED indicates when the charger is in ‘fast’ mode. When the LED goes out the battery is charged and the charger has switched to ‘float’ mode.

6V to 12V DC Voltage Doubler

Here is the 6V to 12V DC voltage doubler circuit design, it also called DC voltage miltiplier or DC to DC converter. This dc voltage doubler circuit will need about 2A from the 6V input supply to produce the full 800mA at 12V for the power output. This circuit is very useful to generate higher voltage from a low power source, but this circuit will deliver low output current. So it should only be used for low current driven applications. Also, the output voltage may be unstable, so a voltage regulator (IC78XX) of proper rating can be used regulation and smooth output. But voltage regulator IC itself consume some current, and reduce the deliverable current.

Power Supply Adapter

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