Showing posts with label supply. Show all posts
Showing posts with label supply. Show all posts
Tuesday, 4 June 2013
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Friday, 12 April 2013
Soft Start For Switching Power Supply
Switching energy provide whose output voltage is drastically lower than its input voltage has a captivating professionalperty: the present drawn by means of it's smaller than its output current. However, the enter energy (UI) is, of course, larger than the output power. There is any other aspect that needs to be watched: when the input voltage at switch-on is too low, the regulator will tend to draw the full current. When the professionalvision can no longer deal with this, it fails or the fuse blows. It is, subsequently, a just right idea to disable the regulator at change-on (via the on/off input). except the related capacitor has been charged. When the regulator then begins to draw current, the charging current has already dropped to a stage which does not overload the voltage supply.
Circuit diagram:
![\"Soft](\"http://2.bp.blogspot.com/_FdGFE8NBDgc/TCxLoy1k-yI/AAAAAAAADt8/T_cLT4biNrk/s320/Soft_Start_For_Switching_Power_Supply_Circuit_Diagram.GIF\")
Circuit diagram:
Soft Start Circuit For Switching Power Supply
The circuit within the diagram provides an output voltage of 5 V and is provided by a 24 V source. The regulator needn't be disabled except the capacitor is fully charged: when the possible throughout the capacitor has reached a stage of 1 of 2 or extra of the enter voltage, all is smartly. This is why the zener diode within the diagram is rated at 15 V. Many regulators produced via National Semiconductor have an crucial on/off change, and that is used within the present circuit. The enter is intended for TTL indicators, and usually consists of a transistor whose base is available externally. This implies that the next switching voltage could additionally be applied by the use of a collection resistor: the worth of this in the existing circuit is 22 kΩ. When the voltage throughout the capacitor reaches a degree of about 17 V, transistor T1 comes on, whereupon the regulator is enabled.
Source: National Semiconductors
Monday, 8 April 2013
Supply Voltage Monitor
A circuit for monitoring supply voltages of ±5 V and ±12 V is readily constructed as shown in the diagram. It is appreciably simpler than the usual monitors that use comparators, and AND gates. The circuit is not intended to indicate the level of the inputs. In normal operation, transistors T1 and T3 must be seen as current sources. The drop across resistors R1 and R2 is 6.3 V (12 –5 –0.7). This means that the current is 6.3mA and this flows through diode D1 when all four voltages are present. However, if for instance, the –5 V line fails, transistor T3 remains on but the base-emitter junction of T2 is no longer biased, so that this transistor is cut off. When this happens, there is no current through D which then goes out.
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Thursday, 28 March 2013
Variable Dc Power Supply
Voltage Range: 0.7V to 24V, Current Range: 50mA to 2A
A variable dc power supply is one of the most useful tools on the electronics hobbyists workbench. This circuit is not an absolute novelty, but it is simple, reliable, "rugged" and short-proof, featuring variable voltage up to 24V and variable current limiting up to 2A. You can adapt it to your own requirements as explained in the notes below.
Circuit Diagram :
Parts:
P1 = 500R
P2 = 10K
R1 = 2.2K-1/2w
R2 = 2.2K-1/2w
R3 = 330R
R4 = 150R
R5 = 1R-5W
C1 = 35V-3300uF
D1 = 1N5402
D2 = 1N5402
D3 = 5mm Red Led
C2 = 63V-1uF
Q1 = BC182
Q2 = BD139
Q3 = BC212
Q4 = 2N3055
SW1 = SPST Mains Switch
T1 = 36VCT-Transformer
Notes:
Circuit Diagram :
Variable DC Power Supply Circuit Diagram
Parts:
P1 = 500R
P2 = 10K
R1 = 2.2K-1/2w
R2 = 2.2K-1/2w
R3 = 330R
R4 = 150R
R5 = 1R-5W
C1 = 35V-3300uF
D1 = 1N5402
D2 = 1N5402
D3 = 5mm Red Led
C2 = 63V-1uF
Q1 = BC182
Q2 = BD139
Q3 = BC212
Q4 = 2N3055
SW1 = SPST Mains Switch
T1 = 36VCT-Transformer
Notes:
- P1 sets the maximum output current you want to be delivered by the power supply at a given output voltage.
- P2 sets the output voltage and must be a logarithmic taper type, in order to obtain a more linear scale voltage indication.
- You can choose the Transformer on the grounds of maximum voltage and current output needed. Best choices are: 36, 40 or 48V center-tapped and 50, 75, 80 or 100VA.
- Capacitor C1 can be 2200 to 6800µF, 35 to 50V.
- Q4 must be mounted on a good heatsink in order to withstand sustained output short-circuit. In some cases the rear panel of the metal box in which you will enclose the circuit can do the job.
- The 2N3055 transistor (Q4) can be replaced with TIP3055 type.
Source: Red Free Circuit Design
Sunday, 24 March 2013
Power Supply Failure Alarm
Most of the power supply failure indicator circuits need a separate power-supply for them-selves. But the alarm circuit presented here needs no additional supply source. It employs an electrolytic capacitor to store adequate charge, to feed power to the alarm circuit which sounds an alarm for a reasonable duration when the mains supply fails. During the presence of mains power supply, the rectified mains voltage is stepped down to a required low level.
Power Supply Failure Alarm Circuit Diagram
A zener is used to limit the filtered voltage to 15-volt level. Mains presence is indicated by an LED. The low-level DC is used for charging capacitor C3 and reverse biasing switching transistor T1. Thus, transistor T1 remains cut-off as long as the mains supply is present. As soon as the mains power fails, the charge stored in the capacitor acts as a power-supply source for transistor T1. Since, in the absence of mains supply, the base of transistor is pulled ‘low’ via resistor R8, it conducts and sounds the buzzer (alarm) to give a warning of the power-failure.
With the value of C3 as shown, a good-quality buzzer would sound for about a minute. By increasing or decreasing the value of capacitor C3, this time can be altered to serve one’s need. Assembly is quite easy. The values of the components are not critical. If the alarm circuit is powered from any external DC power-supply source, the mains supply section up to points ‘P’ and ‘M’can be omitted from the circuit.
Following points may be noted:
1. At a higher DC voltage level, transistor T1 (BC558) may pass some collector-to-emitter leakage current, causing a continuous murmuring sound from the buzzer. In that case, replace it with some low-gain transistor.
2. Piezo buzzer must be a continuous tone version, with built-in oscillator. To save space, one may use five small-sized 1000µF capacitors (in parallel) in place of bulky high-value capacitor C3.
Source :http://www.ecircuitslab.com/2011/11/power-supply-failure-alarm.html
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