I need to build a current source which will output 2 constant using pwm??? can anybody help me here please??? please send me an email ... any help would be appreaciated

plz,clearify about the circuit of this topic. I m so much confused about this.

I used a modification of this circuit around 1995 to output both bipolar voltage and current. It was 16-bit accurate and had no problems around zero in current mode for +/- 20mA with a +/-16V compliance. I worked for HP at the time and the product was a VXI 8/16 channel analog output card. The product number at the time was HP E1418A. You may be able to look up the specs on it on the Agilent website. It was very flexible and with a minimum of switching can be made to output either voltage or current. By the way, I didn't use a zener diode and it works just fine.

It is really good circuit. But i need voltage controled ,0 to 10A constant current source ,Can u help me for that.

It is really nice cicuit and nice explanation. I want use a contant current source to charge 2 NiMH batteries (1.2V each) which are connected in series using 5V input voltage. I want to control the charging current using PWM of the frequency 100 HZ from microcontroller. Can you reply me with the modified circuit....

Thanks for the nice idea!

Rating Only

Can any one tell me how a transconductor can be implemented in spice. I guess a voltage controlled curent source can be used. But how can we justify the use of it ?

How does this work if you have 2 loads that share a common (-) but have independant (+) and you want to use this circuit twice with each circuit supplying an independant current to each load, but they share a common (-). Would this work?

ya i need current control of an inverter (150 W).i want to use LM324. Who can help me. Please e-mail to me for helping. i need it :( dellnegrowachi@hotmail.com

ya i need current control of an inverter (150 W).i want to use LM324. Who can help me. Please e-mail to me for helping. i need it :(

Very practical one, I use exactly the same current source in my project and works excellent!!

Can we create current pulses with this circuit? I need to generate +-100 mA with an adjustable DC current of 0 to 2A

I want to know more about the designing of current source controlled by microcontroller. Can I get the article

Can we use this circuits as bidirectional current source? or do we need any modification?

Bob

Simple changes made great improvements to the Holand current source! This circuit has been around a long time, but these modifications make it more useful and more accurate.

Gabriela Vergara Senior Electronic Designer Adesco Inc.

Heck, I have been using this circuit for more than 25 years. Extensive calculations have been shown for years, Motorla had an application note about it and I know I still have it since I read it about 10 months ago.

I have used it in bi-directional low ( Microamps) to high (Amps) current circuits.

Primative circuit, not the stuff of a seasoned engineer. I have used a better circuit for over 15 years that provides bidirectional current control with just 2 op amps. Can use it for power, sensors, filters, gyrators, long term integrator, etc... Also has very low TC concerns. I recommend you looking at designing circuits that depend on ratios rather than absolutes to solve TC issues.

This current source is a great design for medium range accurcy for varibale range but for class A industries it may not enough accurate specially for low current application!

This current source is a great design for medium range accurcy for varibale range but for class A industries it may not enough accurate specially for low current application!

Great idea, it is very nice that a positive feedback works like this!! May be a stability analysis of the circuit be a good idea too.

i want to make a current amplifier using LM324.plz help.

i want to built a constant current source. i want to use it with the circut which will decect the PCB track short. Plz help me

I want to build a constant current source. I want to use it with the circut which will detect the PCB track short. Please help me.

If you want max. 200 mA current; then R = 5 Volt / 200 mA = 25 Ohm

for 10 mA = Vin / 25 ==> 250 mV for 200 mA = Vin / 25 ==> 5000 mV

and you provide analog voltage from MCU with PWM. ok?

i want to control a constant current source from 10ma-200ma using microcontroller so please send me designing of such current source

The circuit looks good.It seems to have a drawback. The output current will never be zero. For a zero ohm load the current through the 2 100K resistors will flow through the output . For the voltages shown the minimum current achievable is 74 microamps, which may not be acceptable for low full scal ranges.

This is a very practical circuit, I built this and it works excellent under a lot of load variations. Excellent idea!!

Mike Tallevi

This is a very practical circuit, I built this and it works excellent under a lot of load variations. Excellent idea!!

Mike Tallevi

"Using four resistors as the current sampling resistor will have the same temperature co-efficient as the TC of one of them. So??" Yes, but the current, and therefore the heat-generating power, will be divided among the resistors for less change.

This is a nice circuit.

This positive feedback looks unstable??!! How it works?

Nice circuit. Can you tell me the modifications I have to make for it to work for high current, i.e up to 10 A and 13 V?

Thanks for a lot of help! and be patient with my emails.

Instead of U1 and the precision 100k resistors, use a difference amplifier like INA105. To improve precision, use a dual op-amp (lm358) in place of U2. Place the second op amp in the feedback (V2 to -input). This compensates the U2 for thermal effect because its feedback is also afected by the temperature reducing offset at V2.

I am quite excited. I could do a current modulation up to 60 kHz for a twisted wire with 100 ft (29 ohms and 1.7 mH inductance)!!! Thanks. This circuit speeds up my project. What other changes do I need to have for a current modulation for 5-mH transmission line up to 100 KHZ? Would you help me?

Very nice improvement and refinements to the basic Howland current source. It broadens the useful range, and widens the possible uses of the simplified basic concept. The multiple resistor allow me to spread the heat around, and allows the use of, off the shelf, inexpensive parts.

I was in need of a simple current source and I found this circuit through Google. I used LM324 instead of LM321 and 2N2401 to build this circuits and it works excellent!! It's linear in all range of current and load. Thanks for your article. I'm looking for next one! Keep it up!

Manda BC/Canada

Terrific idea!! I like the calculations, but I can't understand why we multiply VZ by 2 in the last formula????

This is interesting-- four resistors in parallel reduce the heat on each resistor and lower change because of temperature change! That's true.

This is a variation of Howland circuits, but here are the improvements: 1) Current accuracy is higher, because we use a buffer for sampling of the load voltage 2) Howland circuits doesn't work linearly for lower current settings, this is solved by that zener diode 3) Using four resistors in parallel obviously doesn't change the thermal coefficient of the equal resistor, but it reduces the temperature rise on each of the resistor so makes it more accurate.

Isn't this a variation on the Howland current source?

This is exactly the Howland current source known for many years, so what's new? Using a transistor buffer to increase current capability is hardly an innovation. Using four resistors as the current sampling resistor will have the same temperature co-efficient as the TC of one of them. So??