Wiring Schematic Diagram

Volt regulators such as the LM78xx series sometimes need to provide a little bit more current then they actually can handle. If that is the case, this circuit can help out. A power transistor such as the TIP2955 or similar can be used.

The power transistor is used to boost the extra needed current above the maximum allowable current provided via the regulator. Current up to 1.5 A will flow through the regulator, anything above that makes the regulator conduct and adding the extra needed current to the output load. It is no problem stacking power transistors for even more current. Both regulator and power transistor must be mounted on an adequate heatsink.

A switching voltage regulator circuit shown here can be a low cost solution for your high efficiency requirement electronic circuit design. This regulator circuit  can deliver up to 3A of current. The input voltage range of this circuit is between 8 to 35V DC and the output voltage can be adjusted between 1.8 to 32V DC. The output voltage can be adjusted by using the POT R4

The circuit uses a standard linear regulator LM317 IC. LM317 regulator IC provide a stable internal voltage reference, and provide the adjustment method. This wide-range output voltage adjustment make it suitable for general purpose power supply in lab application.

When compared to linear voltage regulators the switching voltage regulators are much power efficient. In the case of linear voltage regulators the difference between the input and output voltage is just wasted and for switching regulators there is almost no such wastage and that’s why the switching regulators have great power efficiency ranging up to 85% . In simple words, the switching regulator operates by taking small bits of energy from the input voltage source and then transferring it to the output with the help of a solid state switch and a control circuitry. Since the switching element is either fully open or closed at any moment, no energy is wasted across it. The control circuit controls the duty cycle of the solid state switch which in turn determines rate at which energy is transferred to the output.

A 12VDC overvoltage protector circuit is shown in the schematic diagram below. This circuit will work to disconnect the protected device from the power supply when an overvoltage occurs at the supply. This circuit uses a silicon-controlled rectifier (SCR) and normally-closed 12-V relay, K1. The silicon-controlled rectifier is connected in parallel to 12-V line to monitor for the overvoltage condition. This applied signal is sensed by the SCR’s gate.

Until the voltage drops below the set value, the K1′s contacts remain closed and SCR1 remains off. The SCR1 will be triggered causing K1′s contacts open and halt current flow to the loas when overvoltage occurs. You can use R1 to set the trigger point of SCR1

This Power Supplay circuit is constructed for the use with 100Watt transceivers. When you build the unit you should care for a good kooling of the finals. The next thing is to provide at least 2500uF pro Ampere you want to pull out of it. You can get more current out of the circuit by adding more final transistors to it. Except of the emitter resistors all of the other ones are for 0,5 Watts typs.

The L200 is abel of regulating the voltage as well as the current. The TAG 226 and the zener-diode are there to protect the attached equipment against overvoltage. The power-supply is adjusted to run at 13.8V and the zener-diode is a 14V type, so as soon as the voltage gets to 14V the thyristor will be switched and produces a shortcut, and blows the 20A fuse. To use the circuit with this handbrake at higher voltages you should replace ZD14 against a higher one. Or make an adjustible krowbar that runs simultanuesly with the voltage


This power Supplay Circuit From http://www.mydarc.de/dl5dbm/20a_e.pdf

Most good bench power supplies include a form of overvoltage protection, but for those power supplies or for other applications where over voltage protection is required, a simple over voltage crowbar circuit can be built. It uses just four components: a silicon controlled rectifier or SCR, a zener diode, a resistor and a capacitor.

The SCR over voltage crowbar or protection circuit is connected between the output of the power supply and ground. The zener diode voltage is chosen to be slightly above that of the output rail. Typically a 5 volt rail may run with a 6.2 volt zener diode. When the zener diode voltage is reached, current will flow through the zener and trigger the silicon controlled rectifier or thyristor. This will then provide a short circuit to ground, thereby protecting the circuitry that is being supplied form any damage.

However it is necessary to ensure that the power supply has some form of current limiting. Often a fuse is ideal because the SCR will be able to clamp the voltage for long enough for it to blow. The small resistor, often around 100 ohms from the gate of the thyristor or SCR to ground is required so that the zener can supply a reasonable current when it turns on. It also clamps the gate voltage at ground potential until the zener turns on. The capacitor is present to ensure that short spikes to not trigger the circuit. Some optimisation may be required in choosing the correct value although 0.1 microfarads is a good starting point.

This circuit can clearly show the level of the supply voltage as long as the indicator has good 12 volts at its input, LED1 gives steady, uninterrupted yellow light. If the input voltage falls below 11 V, LED1 will start to blink and the blinking will just get slower and slower if the voltage drops further - giving very clear and intuitive representation of the supply's status. The blinking will stop and LED1 will finally go out at a little below 9 volts. On the other hand, if the input voltage rises to 13 V, LED2 will start to glow, getting at almost full power at 14 V. The characteristic voltages can be adjusted primarily by adjusting the values of R1 and R4. The base-emitter diode of T2 basically just stands in for a zener diode.

Voltage Indicator Circuit For 12V Power suplay

The emitter-collector path of T1 is inversely polarized and if the input voltage is high enough - T1 will cause oscillations and the frequency will be proportional to the input voltage. The relaxation oscillator ceases cycling when the input voltage gets so low that it no longer can cause breakdown along the emitter-collector path. Not all small NPN transistors show this kind of behavior when inversely polarized in a similar manner, but many do. BC337-40 can start oscillations at a relatively low voltage, other types generally require a volt or two more.

A simple but less efficient method of controlling a DC voltage is to use a voltage divider and transistor emitter follower configuration.

The schematic diagram above illustrates using a 1K pot to set the base voltage of a medium power NPN transistor. The collector of the NPN feeds the base of a larger power PNP transistor the which supplies most of the current to the load. The output voltage will from be about 0.7 volts below the voltage of the wiper of the 1K pot so the output of cans be adjusted from 0 to the full supply voltage minus 0.7 volts. Using two transistors Provides a current gain of around 1000 or more so That only a couple milliamps of current is drawn from the voltage divider to supply a couple amps of current at the output. Note That this circuit is much less efficient Than the 555 timer dimmer circuit using a variabe duty cycle switching approach.

In the schematic diagram above, the 25 watt / 12 volt lamp draws about 2 amps at 12 volts and 1 amp at 3 volts so the power lost Pls That the lamp is dim is around (12-3 volts * 1 amp) = 9 watts. A Fairly large heat sink is required to Prevent the PNP power transistor from overheating. The power consumed by the lamp will from be only (3 volts * 1 amp) = 3 watts Gives us the which an efficiency factor of only 25% Pls the lamp is dimmed. The advantage of the circuit is simplicity, and Also That it does not generate any RF interference as a switching regulator does. The circuit cans be Used as a voltage regulator if the input voltage Remains constant, but it will from not compensate for changes at the input as the LM317 does.

This transformerless power supply circuit will of supply up to about 20mA at 12 volts. It uses capacitive reactance instead of resistance, and it does not generate very much heat.The circuit draws about 30mA AC. If you need more current, use a larger value capacitor, or put two in parallel, but be careful of what you are doing to the Watts. The low voltage 'AC' is supplied by ZD1 and ZD2. The bridge rectifier cans be any of the small 'Round', 'In-line', or 'DIL' types; or Could you use four separate diodes.

This power supply can not be modified to Provide currents of greater (can not be up to several amps). The circuit was Designed to Provide a cheap compact power supply for Cmos logic circuits require only A Few That milliamps. The logic circuits were the resource persons then Used to control mains equipment (fans, lights, heaters etc.) through an optically isolated triac. If More Than 20mA is required it is possible to increase of C1 to 0.68uF or 1uF and thus obtain a current of up to about 40mA. But 'suppressor type' capacitors are Relatively big and more expensive Than Regular capacitors; and Increasing the current That means higher wattage resistors and zener diodes are required. If you try to Produce More Than about 40mA the circuit will from no longer be cheap and compact, and it simply makes more sense to use a transformer.

C1             : 470nF/500V
C2             : 100µF/25V
R1             : anything from 1MΩ to 10MΩ
D1, D2, D3, D4 : 1N4007 or rectifier 230V AC
D5             : zenerdiode 12V or matching Uout desired