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Regulating Minimum Voltage

March 8, 2015, 3:00 pm
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Is it possible to construct a circuit that outputs a voltage of 0 below a certain threshold , similar to a Schmitt Trigger, without using op-amps?

In my circuit I want to prevent input voltage below 6.8V from reaching the capacitor C2. The input with the switch set up as in the picture, is 7Vrms AC Voltage which has been rectified and regulated to 7V. The circuit is supposed to charge the capacitor when the switch is flicked up and discharge the capacitor when it is flicked down. But I dont want the capacitor to charge when the input voltage is below 6.8V. When I attached a Zener diode in front of the capacitor I did not get any output voltage across C2.

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L705CV Voltage Regulator Overheating [duplicate]

March 12, 2015, 4:00 pm
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Why doesn't my TL071CP op amp act as a voltage follower?

March 29, 2015, 5:00 pm
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I have the TL071CP op-amp, and I am trying to make a simple DC voltage follower, however, I only get a couple hundred milivolts at the output. Usually 200-450mV. Any idea why?

Image may be NSFW.
Clik here to view. schematic

simulate this circuit – Schematic created using CircuitLab

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How to design capacitance value for a given full wave rectifier [duplicate]

April 3, 2015, 7:50 pm
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Excessive Boost Converter Output

April 7, 2015, 9:00 am
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I’m implementing a boost switching regulator based on a Texas LM5002 chip (datasheet), to get about 65V from a 12V supply. The design I’ve arrived at is shown below, inspired both from the data on the datasheet and the information here. I was not able to get all the parts with the necessary values, but I used the closest values I got my hands on. The design took into account an input current of about 50 mA to supply about 1mA on the output node.

Image may be NSFW.
Clik here to view. schematic

simulate this circuit – Schematic created using CircuitLab

Problem is, when I tie 12V to the input, I get, for a few seconds, around 900V (???), before the output shorting to ground. What is exactly could be causing this? Have I got something wrong on my circuit?

EDIT: It appears I made a mistake on my original question while drawing the schematic, the actual value of R4 is 1.6k and not 100 ohms.

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LM317, principle of operation

April 9, 2015, 8:50 pm
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I have found a schematic explaining a LM317, principle of operation.
The way I read the diagram, the non- inverting op-amp input (+) is always going to be at the ‘INPUT’ level,
and doesn’t matter what the adjust voltage is.

I am wondering if they should have a resistor where they have the circle for the adjust current. Lower voltage on adjust would then lower the voltage on the non- inverting input.

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voltage regulator connected between positive and negative voltages

April 14, 2015, 5:50 pm
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I’m kind of new to the world of electronics, so bear with me.
I need to regulate +24 volts down to about +21 volts (for supplying a really pretentious heating resistor). I already have the circuit for the v-reg using +24v. The problem I’m having is that I don’t have +24 volts, but I do have +12 and -12 volts. Could I connect the input of the v-reg to +12v and use the -12v as the circuit’s GND?
The voltages come from a PC PSU.

This is basically what I need:

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Clik here to view. This is basically what I need

EDIT: I calculated the output as +9V. Combined with -12V the load should get 21V, right?
But now I’m not sure about what I use for the ULN2003′s ground? Should I use the actual GND or should I leave it to -12V.
Thanks.
Image may be NSFW.
Clik here to view. Could this work?

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Need to make sure Thyristor switches off with rectified AC

April 19, 2015, 6:00 pm
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So I have full-wave rectified AC from mains and the following circuit which is basically a AC dimmer that takes slices of that for a much lower total average voltage.

(Voltage source is labeled as an offsett-ed “triangle” below as I thought it approximates it best for now, damn simulation kit doesn’t even have a bridge rectifier…)

Now, it’s important that the Thyristor turn off at 0V of the rectified AC, so the cycle start anew of turning the Thyristor on and off. But I’m utterly unfamiliar with rectified AC and don’t know if the current will absolutely 0A at 0V, though I know a resistor on AC is perfectly phased with voltage… I don’t know, even maybe C1 or C2 might change the intended results…

Or, is it enough for me to pick a Thyristor whose Holding Current is in the hundred microamps range (or higher), so it cuts off??

EDIT:

Also, does C1 and C2 both have to have rating of at least 120V?? Don’t they get charge on max up to 30-34V? That’s specifically why I chose this design… I can choose lower rating capacitors…

Image may be NSFW.
Clik here to view. schematic

simulate this circuit – Schematic created using CircuitLab

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How can I protect this 48VDC device from overvoltage?

April 23, 2015, 2:00 pm
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I’m powering this isolated DC/DC converter from a power supply that is a nominal 48V, but could potentially reach a maximum voltage of 56V. The datasheet for the converter says that the absolute maximum is 54V. How can I protect this chip from the potential 2V’s above it’s maximum?

This regulator is being used to power an isolated MOSFET gate driver.

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Can I dynamically change STM32 voltage during runtime

April 26, 2015, 6:00 am
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I’m using an STM32L151 MCU for a battery powered wireless sensor node. I came across the TPS6274x series switching regulator, who’s voltage can be reconfigured at runtime by flipping it’s inputs. The radio I’m using can only transmit with full power with 3.3v, but it can transmit at slightly lower power at 1.8v. All of my sensors can run down to 1.8v.

Does it make sense to use the control pins of the TPS62740 to boost up to 3.3v only during radio transmission and enjoy the power savings of the 1.8v the rest of the time? What are the implications for the RTC or clock speeds? Do I just need to update the clock configurations when boosting, or are they just good to go?

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Selecting a transistor for high-side switching at 5V with a 2A load current

April 28, 2015, 4:50 am
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I’m doing a high side switching of 5V 2A load and will be ON or OFF for long time(1-10 hours).

Now I’m confused about which transistors should I use ? or MOSFETs ? Do I need heatsink ? I really prefer SMD transistor or MOSFET, if its possible ?

I also want 5V on other side of transistor/MOSFET too. I’m sure there will be voltage drop, is there any way to get back the voltage drop ? First I thought to use bit high voltage in switching like 7V then put voltage regulator on other side so I can get right 5V. But since the load is 2A. The power will be 10W if I’m not wrong. Then I think its too much heat.

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Combine multiple voltage regulator?

May 2, 2015, 8:00 pm
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Maybe this is very stupid question but I want to know if I can connect two or more voltage regulator (like LM7L05) to add ampere? Say if 1 is able to source 100 mA then combine 2 to draw 200 mA? Sorry if this sounds stupid!

Note: I know I can search regulator to source more current but in this question, I would like to understand that if I can connect multiple regulators together!

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Can a voltage regulator or stabilizer increase voltage and current simultaneously when used with a generator?

May 2, 2015, 8:00 pm
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I have just built a generator with a stepper motor I found in a photocopier/printer (24VDC, 0.7A) and a transformer. Without load, the voltage is around 406 VAC. With a bulb (230 VAC, 18 W), the voltage drops to 240 VAC.

Can a voltage regulator or stabilizer be of any help in making this generator power a number of household equipments?

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433 Mhz + Attiny85 improve range

May 4, 2015, 3:50 pm
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I want to send information from my Attiny85 to my Raspberry.
For the moment.
Attiny and Emitter work on 5V
Emitter have a 433 Mhz 1/2 waveform antenna Image may be NSFW.
Clik here to view. 433 Mhz 1/2 waveform antenna
I’am using virtual wire

Raspberry receiver work on 5V with 430 ohm resistance for data.
I use vw.py python program

All this work fine 0-1 meter, badly (10%) at 2 meters and not at all more far away.
Problem, my desk is about 4m far away the Emitter. How can I improve this range ?

My idea : Using 12v input for emitter with 7805 for Attiny and a low cost NPN transistor between Attiny data pin, 12v and data of emitter.

Is my idea good ?
Do you have other idea ?

Thanks

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Selection of charge controller to charge Lithium Ion battery

May 4, 2015, 10:00 pm
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I have a DC generator with an output voltage of 27.5 Volts and current of 102 Amps. I need to use this charge my 24V 100Ah Lithium ion battery. So, I need to put a charge controller in between to charge my battery and protect it from over charging. What spec charge controller should I go for this purpose ?

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low dropout regulator output voltage

May 6, 2015, 7:50 am
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I want to use the DMOS low-Dropout regulator REG102 3V3, but in the datahseet REG102 of the regulator i found two configuratons. The first configuration is without resistors divider and by connecting a capacitor on the output. The second configuration is with voltage divider,in this configuration the voltage Vout is depending on the values of the resistors and voltage Vref as is shown in the figure below:
Image may be NSFW.
Clik here to view. REG102 with resistors
My question is :
How the voltage Vin influence the voltage Vout in case of use of the voltage divider ?

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Is there a voltage buck converter which also boosts output current?

May 7, 2015, 4:50 pm
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Application: solar USB charger.

I have a 9V solar panel. I use a buck converter circuit to bring it down to 5V before going into the USB battery charging circuit.

Exact components:

http://www.amazon.co.uk/gp/product/B00I0MOVBO
http://www.amazon.co.uk/gp/product/B00EYT1DWW

This link has more information about the buck converter circuit (I think it’s the same one I bought from amazon above):

http://www.minikits.com.au/LM2596-PSU-01

I was hoping that the buck converter would also increase the output current (say, for example, from 333mA to 450 mA, for a ~75% efficiency), but after measuring it, it seems to track exactly the input current (Ioutput = Iinput). That’s why I didn’t simply use a 7805 regulator, which I understand dissipates extra power as heat: I was hoping that the buck converter circuit would convert more efficiently, and translate in increased output current.

Are there any alternative buck converters (PCB or a design that I could build myself) which would reduce from 9V to 5V while also increasing the current somewhat? If yes, in practice, would their efficiency be worth it? (I think that anything below ~75% efficiency might not be worth it for such low power).

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Constand output voltage from batteries / rechargable batteries

May 12, 2015, 6:00 pm
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I’m trying to make myself a battery pack for my DSLR camera.

The original battery of the camera has 7.2 V and 1200 mAh.

I’ve also bought a coupler ( a dummy batterie for external DC input ) which has a AC/DC adapter with 8.4 V and 2000 mA output.

So I am pretty sure, the camera can hadle anything between 7.2 V and 8.4 V input voltage.

I was thinking of using two 6x AA battery clips.

So if I wire the battery clips like so ( seriel & parallel ):

[##]   <--  AA battery


+--[##]---[##]---[##]---[##]---[##]---[##]--+
|                                           |
+--[##]---[##]---[##]---[##]---[##]---[##]--+-----  (+)
|                                                         INPUT
+-------------------------------------------------  (-)

…I should either get:

A. Using normal AA batteries:

6 x 1.5 V = 9 V

B. Using rechargeable AA batteries:

6 x 1.2 V = 7.2 V

So is there an effective way I can get a constant output with anything between 7.2 V and 8.4 V ??

thank you.

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Microcontroller controlled power supply

May 12, 2015, 11:50 pm
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Can anyone assist me to make a power supply whose output voltage will be controlled by an Arduino, with the latest voltage setting automatically saved in non volatile memory?

I am in an OJT (On the Job Training Scheme). I was given a task to make a Arduino controlled voltage variable power supply whose outputs can be switched between several preset values using pushbutton control. It’s like switching between two different outputs when a designated button is being pushed.

Here is what I have done so far. I made an LM317 based power supply with the output voltage controlled by a potentiometer. I followed this youtube tutorial. It works well but I was ask to upgrade it.

Instead of using a potentiometer to adjust the voltage, I wish to use switching buttons to choose between two or more preset voltage levels. Each switch buttons have their corresponding voltages.

This link may also be relevant.
Code is given below the circuit diagram.
ARDUINO AS A POWER SOURCE ALTERNATOR

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How to regulate 29VAC down to 24VAC?

May 12, 2015, 11:50 pm
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I have a power supply that says it is 24VAC output, but in reality is is giving a steady 29VAC of output. Is this normal? I am powering sprinkler solenoids that say 24VAC. So my question is how can I drop the voltage so I can supply 24VAC. I found some buck converters, but they seem to be DC only or AC input and output DC. I am assuming resistors might work, but an unsure of how to calculate for AC, and wondering if there is maybe a specific device that is made for this purpose?

I have done some work in DC, but AC is kinda new territory, so any help/explaination is much appreciated!

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