Power supply circuit » Variable power supply http://apowersupply.com Sat, 19 May 2012 07:51:49 +0000 en hourly 1 http://wordpress.org/?v=3.1 Variable Power Supply with 78XX regulator http://apowersupply.com/variable-power-supply-with-78xx-regulator-242.html http://apowersupply.com/variable-power-supply-with-78xx-regulator-242.html#comments Sat, 12 May 2012 05:49:18 +0000 aPowerSupply.com http://apowersupply.com/?p=242 This variable power supply is using 7805, 7809, 7812 or 7815 voltage regulators, where the last 2 digits represents the maximum output voltage of the IC. This circuit offers excellent ripple rejection, eliminates mains hum, and has a design using a pi filtered C-L-C.

A core should be chosen to work within the specific frequency as stated by the manufacturer. L1 is a powder core and has 32 turns of 0.75mm wire.

Variable Power Supply Circuit Diagram

variable power supply 78xx regulator
The transformer has a 240V primary and has a secondary rated 24V at 2A. The bridge rectifier contains 4 diodes, their current rating needs to be high with respect to the transformers output current; if not the current may damage the diodes. C1 is the mainfiltering capacitor, the supply is further smoothed by the combination of L1 and C3. C2 and C4 are decoupling capacitors; their action further reduce ripple factor.

The regulator 78xxr, U1 utilizes the action of zener diode ZD1 which is in parallel with the potentiometer, R1. The tuning action of R1 produces a variable regulator output. The output voltage is variable from the regulator output to the regulator output plus the zener voltage. E.G. A 7805 regulator and 10V zener give an output adjustable from 5 to 15 Volts. The regulator may be changed to provide different output voltages as may the zener. the zener should be rated a minimum of 1.3 Watts.

T1 Transformer 10:1 Secondary 24V @ 2A
BR1 Bridge Rectifier 50V PIV 2A rating
U1 7805 N.B. This may be changed for different output voltages e.g. 7812 for higher output voltage
ZD1 15V zener @ 1.3W

Source:http://www.zen22142.zen.co.uk/Circuits/Power/vpsu.htm

]]> http://apowersupply.com/variable-power-supply-with-78xx-regulator-242.html/feed/ 2 Variable Power Supply with UA78G/UA79G http://apowersupply.com/variable-power-supply-with-ua78gua79g-231.html http://apowersupply.com/variable-power-supply-with-ua78gua79g-231.html#comments Fri, 11 May 2012 05:37:38 +0000 aPowerSupply.com http://apowersupply.com/?p=231 A stable variable power supply with an adjustable output voltage from 5 volts to 30 volts can be easily constructed with the regulator ICs UA78G or UA79G. These ICs differ from the common three-terminal regulator since their output voltages are adjustable by a voltage level at their control inputs. The maximum current delivered by these ICs is 1 ampere.

The unregulated voltage must be at least 5 volts higher than the desired output level to maintain stability. The input voltage however must not exceed 40 volts. The maximum dissipation of the IC is 15 watts.

The variable power supply circuit presented here is designed to give maximum voltage level of 28 volts. If P1 is replaced with 25K potentiometer, the regulator can deliver up to a maximum of 30 volts. Capacitors C1 and C2 stabilize the IC and they must be connected as close as possible to the IC terminals.

The IC UA79G delivers negative voltage level. Take note that the two ICs have different terminal connections.

UA78G/UA79G power supply circuit diagram

variable power supply circuit diagram

Variable power supply PCB layout

variable power supply pcb layout and parts placement

]]> http://apowersupply.com/variable-power-supply-with-ua78gua79g-231.html/feed/ 1 3 to 24V Variable Power Supply http://apowersupply.com/3-to-24v-variable-power-supply-387.html http://apowersupply.com/3-to-24v-variable-power-supply-387.html#comments Sun, 22 Apr 2012 21:59:16 +0000 aPowerSupply.com http://apowersupply.com/?p=387 This 3 to 24 volt variable-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). 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.

Voltage regulation is controlled by 1/2 of a 1558 or 1458 op-amp. 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. The maximum DC supply voltage for the 1458 and 1558 is 36 and 44 respectively. 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 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 3 amp output is obtained using the center tap of the transformer with the switch in the 18 volt position. All components should be available at Radio Shack with the exception of the 1558 op-amp.

Variable Power Supply Circuit Diagram

variable power supply

]]> http://apowersupply.com/3-to-24v-variable-power-supply-387.html/feed/ 0 Variable power supply http://apowersupply.com/2n3055-variable-power-supply-164.html http://apowersupply.com/2n3055-variable-power-supply-164.html#comments Sun, 05 Feb 2012 16:13:44 +0000 aPowerSupply.com http://apowersupply.com/?p=164 This simple variable power supply circuit has a low production cost and delivers an output voltage between 1,5 V and 15 V with a 500 mA maximum current. Its stabilization is better than 2% if the current consumption do not exceed 350 mA. The variation of the power supply voltage can be made with a potentiometer and when overloading occurs a buzzer sounds a alarm.

T4 compairs the P1 slider voltage with the output voltage. Then the P1 slider voltage is 0,65 V higher than the adjusted voltage, T2 opens, which stops the T3-T5 Darlington base current.
The 18V, 1A transformer voltage must be filtered with B1 and C1. When the output current is more then 500 mA, the Bz1 starts the alarm (overloading). Bz1 must be a 24 V type, auto-oscillating.

2N3055 variable power supply schematic

variable power supply diagram
This dc variable voltage power supply has not been tested.

]]> http://apowersupply.com/2n3055-variable-power-supply-164.html/feed/ 3 Amplitude modulation power supply http://apowersupply.com/amplitude-modulation-power-supply-108.html http://apowersupply.com/amplitude-modulation-power-supply-108.html#comments Sat, 28 Jan 2012 13:54:51 +0000 aPowerSupply.com http://apowersupply.com/?p=108 Modulated power supply is necessary for final stages of AM transmitters, transmitters with Gunn diodes in GHz frequencies. This amplitude modulating supply provides (in idle mode) an output voltage which can be adjusted with P1 between 6 and 8V; and when is modulated the output voltage is between 3 and 10V. Frequency domain is from 200Hz to 30kHz.
Without external load, the current consumption is 5mA. If T2 is cooled enough the modulation power supply cand deliver up to 800mA at 6V.

AM power supply circuit schematic

AM power supply

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