# Questions tagged [constant]

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### How to make a current source that supply constant current independent of a voltage power supply?

I want to design the simplest possible circuit that drives a led. The led must load the same amount of current whatever the voltage is at the input, between 5 and 9 Volts. The current could be 10mA. I ...
64 views

### How to make a proportional current output on a constant current driver with PWM dimming

I'm making a constant current LED driver out of 2 2N2222 transistors and a couple of resistors. Works great. I added a PWM signal to the input so I could dim the LED, also works great. The problem is, ...
255 views

### Ohms law's statement

Is this correct: "Current is directly proportional to voltage if resistance kept constant" V = I*R Ohms law is only applied when resistance kept constant or not?
81 views

### What could happen if I touch a constant current source for example 5 Volts 1 Amp..?

Yes, I am talking about a constant current source not a voltage source. Would the 1 Amp go to my body?
59 views

### DC Electronic Load in Constant Impedance Mode

I have an Electronic Load module that allows the UUT to be loaded in either Constant Current (CC), Constant Voltage (CV), Constant Power (CP), Constant Resistance (CR) or Constant Impedance (CZ) mode. ...
60 views

### Howland source, MAX current output?

How would one determine the maximum current output you could achieve from an improved Howland source given a specific Op-Amp? ie. What do I need to look at in the Opamps datasheet? (I am using a ...
94 views

### PCB Layer Stack Dielectric Constant Math

I have a question reference PCB layer stack and the adding multiple dielectric constants together. The image and description below should help clarify the question: The differential pair will be ...
69 views

### I'm working on a school Lab for a Constant Current source BJT and need a nudge in the right direction

I am stuck trying to determine the applicable formula for the load current. I have used $I_b = \frac{Vin-Vbe}{(Beta+1)*Re}$ and then $I_L= (Beta)*I_b$. The problem is I can't find a proper ...
117 views

### Trouble getting AL8861 LED Driver to illuminate LEDs

I am trying to get a AL8861 LED driver hooked up. Right now I've connected it to a single LED (this one) to test (see circuit below). I eventually intend to connect it to a DAC5578 Digital to Analog ...
249 views

### MOSFET Constant current - Current mirror circuit

I have been reading this current mirror/constant current circuit using MOSFET. MOSFET Constant-Current Source How does the current not change through Q2 when the voltage at Q2 increases? Ref.Fig1 ...
522 views

### Capacitor charging efficiency with a constant power source

I have a question. It is easy to derive the efficiency for loading a capacitor from a constant voltage or a constant current source, basically because exponential functions and constants are very, ...
148 views

### Trying to split the current output of an LED driver

I am currently using an 8 channel LED driver wher I have set the outputs to produce 20mA of constant current. Problem is I have 11 LEDs to drive. So I have decided to connect two LEDs in paralled to ...
2k views

### Making an efficient constant current source

I need help making an efficient constant current driver. I want to power my home with LED light strips for lighting and decorative purposes. I need to be able to turn each strip on and off ...
132 views

### Internal constant current driver for LED short circuits and blows when connected to AC main (120v) without DC load

I have AC 85-265V to 0.3A 8-12W DC 22-40V Internal constant current power supply for LED spot lights. This is the exact model https://www.lightinthebox.com/en/p/0-3a-8-12w-dc-22-40v-to-ac-85-265v-...
130 views

### Connect VGA cooling fan (12vdc - 0.1A) to constant current driver (120Vac to 12- 22vdc @ 0.3A)

I have an AC driven COB LED which can be connected directly to the AC main in house (120v). I would like to attach a cooling fan to the COB which requires 12vdc @ 0.1A. I have a constant current ...
2k views

### how to pass parameter variable to module in verilog

I need some help changing dynamically parameters of one module I'm trying to extract part of network data that it comes from the top module and goes to the internal modules In specific I have one ...
560 views

### Implementing a constant current source circut that can be switched off by a voltage signal

Does anyone know how to implement a constant current source circuit that is able to output 10mA constantly, ideally the load of the circuit would be a 100uF capacitor in series with 100 Ohms. Is ...
74 views

### Wiring a voltage specific device onto a constant current circuit?

I've got a bunch of LEDs wired in series to a constant current driver. The driver runs the circuit at 500ma to 700mA (I can vary it up or down a little) and can supply 50 to 100 volts, maximum 60 ...
134 views

### RC time constant in circuit with two caps with different potential

I'm trying to develop a model for the switching speed of a MOSFET. In reducing the equivalent diagram I have come up with this circuit with a resistor and two capacitors in parallel. The catch is ...
79 views

### Analysis of Buck COnverter

In an analysis of buck converter, we make few assumptions. Those are: The circuit is operating in steady state. The inductor current is continuous. The capacitor is very large and the output voltage ...
559 views

### Associate std_logic_vector constant with input port VHDL-200X

I am trying to configure a chip over SPI interface using FPGA Spartan 6 Eval board. I just need to configure, I do not need to read the data from the chip, it will be done by another interface. ...
192 views

### Understanding constant current circuit

I've been learning about different constant current circuit designs and just recently stumbled upon this one. All I know is that the highlighted resistor is the load resistor and when varied, like a ...
868 views

### Calculating Slew Rate from a time-constant

I have to choose an OP-AMP mainly based on slew rate. I am using the op-amp as a differential comparator with dynamic (time) hysteresis with a time-constant 3*tau=500Āµs. My upper threshold of the ...
103 views

### Relation between current and used energy

Thinking about a dc motor and a constant voltage battery, if you slow down the motor by resisting it physically without stopping it, its resistance increases, right? Therefore reducing the current in ...
226 views

### My RC Time Const. Calculations are wrong. Circuit changes my input signal

I have a simple RC circuit of 22 ohms and 3.3uF My measured values put the resistor at 22.10 ohms and the cap at 3.15 which gives me a time constant of 68.5 uS The signal applied is a 100Hz Square ...
138 views

### Parallel Regulator

Can anyone tell me how it works? In my opinion when U+ = U- the voltage Uo is constant no matter of the load resistor(R5). But this is only if U+=U-.
48 views

### Technology “dielectric constant” information

OK, so when working in a technology, say Bipolar, to build a high frequency amplifier, can I trust that the dielectric constant info for the various films contained in the electrical design rules, are ...
988 views

### Why does large inductance have a constant current through it?

I wanted to know, if an inductor is large, why would the current through it be constant? If an inductor is large, it means that it would be an open at moderate frequencies, and at DC the inductor is a ...
521 views

Can someone tell me am i right? In constant voltage mode op amp compare voltage on noninverting input with voltage on inverting input and when U+ is larger than U- the load MOSFET turns on? If someone ...
1k views

### unstable pwm constant current

I am building a four channel constant current LED driver with PWM control. I have used the following circuit (replicated four times off a quad op amp). The circuit functions OK but as I wind the set ...
1k views

first wanna thank anyone who can provide some thoughts on this. My doubt now is this. I'm using some meanwell power supplies and I'm a bit confused about max output they can handle. For an ...
489 views

### Low voltage, high current LED driver IC— does it exist? [closed]

I need an LED driver that can operate from a supply voltage as low as 3.3 volts and can put out a current of 350 mA or higher. The LEDs I'm using have a forward voltage of 2.7 volts at 350 mA. I only ...
667 views

### What is the formula for the dependence between modulating input voltage - output current for two transistor constant current sink

In a constant current sink from the two npn transistors, load and sensing resistor, application of increasing voltage on the base of the transistor produces practically linear increase in output ...
108 views

### Why do I get constant voltage across load of single phase inverter even with increasing input voltage

I built a single phase inverter, as shown below. However, for PWM gate control signal of maximum 9V peak, i noticed that the output PWM voltage across the a 10k resistive load does not increase above ...
103 views

### MOSFET has constant current

I have the following simple circuit. However, when I put the multimeter on the receiving end I'm always getting a current and I can't shut the gate, can anyone help please? I'm using the following ...
2k views

### DAC controlled constant current source

Was given the task of creating the simplest constant current source that can supply up to 50 mA with an ~700 ohm load. I can use any IC's out there. I stumbled across the chip here from linear tech: ...
1k views

### Precision voltage reference divider vs. constant current source to drive an RTD sensor

I need to measure temperature with an RTD between 0-300 C. I believe I have two options to make this work: A constant current source feeding the RTD A precision voltage reference and a resistor ...
339 views

### What are the constraints when choosing R value for a RC time constant?

I am planning to use a RC circuit to satisfy power up ramp rate requirements. Does the R value depends on system current?
226 views

### PWMing the output of a constant current driver

I have a set of led panels that come with AC-DC constant current drivers. Is it acceptable to use a MOSFET to pwm the LED (MOSFET goes between the driver and the LED)? Also the microcontroller that ...