The power transformer shown is a center tapped 25.2 volt AC / 2 amp unit that will provide regulated outputs of 24 volts at 0.7 amps, 15 volts at 2 amps, or 6 volts at 3 amps. The power transformer should be capable of the desired current while maintaining an input voltage at least 4 volts higher than the desired output, but not exceeding the maximum supply voltage of the op-amp under minimal load conditions. The maximum DC supply voltage for the 14 is 36 and 44 respectively.
The 1458 may be substituted in the circuit below, but it is recommended the supply voltage to pin 8 be limited to 30 VDC, which can be accomplished by adding a 6.2 volt zener or 5.1 K resistor in series with pin 8. Voltage regulation is controlled by 1/2 of a 1558 or 1458 op-amp. The 2N3055 and 2N3053 transistors should be mounted on suitable heat sinks and the current sense resistor should be rated at 3 watts or more. This regulated power supply can be adjusted from 3 to 25 volts and is current limited to 2 amps as shown, but may be increased to 3 amps or more by selecting a smaller current sense resistor (0.3 ohm).
Variable 3 - 24 Volt / 3 Amp Power Supply Other transistors may be substituted such as the TIP29 or TIP31 for the 2N3055 and most any medium power (500mA) PNP for the 2N2905. The 2N3055 power transistor operates as a switch and drops very little voltage (less than 0.5) when conducting, and will not require a heat sink. That should't require a heat sink if several lamps are sequencing but it may get quite warm if the circuit is idle on a single output. The voltage across the PNP transistor will be about 7 volts when it is turned on and the heat dissapation will be about 0.6 watts. The 2N2905/PNP transistor stage is connected as an emitter follower which provides a high impedance to the decoder output and supplies about 80 mA of current to the base of the 2N3055 NPN power transistor which then supplies 2 or more amps to the 12 volt lamp. A 6.8 volt/1 watt zener diode is used in series with the ground connection of all the CMOS ICs (74HC14, CD4516 and 74HC138s) so that the total voltage across the CMOS devices will be about 5.2 volts and the outputs will move from +12 to about +7 when selected. Two additional transistors are used to increase the current from the 74HCT138 decoder to control 12 volt 25 watt lamps. The circuit below is designed to be used with the bi-directional lamp sequencer shown above on this same page. Interfacing 5 volt CMOS to 12 volt/ 25 Watt Loads
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