# Is there a current control circuit to control the amount of current flowing into a circuit?

#### Devika B S

Joined Mar 8, 2017
144
My aim is to design a voltage boost converter with gain being 4. My circuit worked fine with a 9V 500 mAh battery. But as soon as I connected a 12V 1.2Ah lead acid battery, a spark occurred at the point of contact between the battery's positive terminal and solder less bread board. Now I have damaged an inductor, MOSFET as well as an Arduino board. The load is a 300 ohm resistor. I think that the damage occurred because of high input current. But is there any circuit to control the amount of current entering into a circuit?

My specs are as follows. The number in bracket denotes the quantity used. Like (2) in first line means 2 inductors.

Inductor (2) 100 uH, 100 kHz, 2A
Capacitor (2) 22 uF, 50V
Diode (2) 1N5822
Power Mosfet (1) IRLB8748 (This is a logic level power MOSFET triggered by an Arduino)
Battery (1) HW 9V Carbon Zinc Battery 6F22 (or) 12V 1.2Ah lead acid battery which damages everything
Arduino Uno R3 (1)
Resistor - 100 ohms (3) So total r = 300 ohms when connected in series.

#### wayneh

Joined Sep 9, 2010
16,129
Schematic?

#### Devika B S

Joined Mar 8, 2017
144
Schematic?

The above is the schematic diagram.

The above is a photo of the actual hardware used. The 9V battery has an open circuit voltage of 7V. A 1k resistor is used in pic (instead of 300 ohms). But I have also done this with 3 100 ohms load. When connected, the battery terminal just measures around 4.5 V. When I connected the 12V battery (on top left corner in the pic), the damage occurred.

#### hp1729

Joined Nov 23, 2015
2,304

Per your request for a current limiter circuit. Current limit is set by selecting a resistor. R2 or R9 sets the current limit. 0.6 V / R.

#### Devika B S

Joined Mar 8, 2017
144
View attachment 123349
Per your request for a current limiter circuit. Current limit is set by selecting a resistor. R2 or R9 sets the current limit. 0.6 V / R.
Is the above a PWM current controller? (I need a PWM current controller instead of a current limiter) The entire circuit needs PWM programmed by the Arduino.

#### Alec_t

Joined Sep 17, 2013
10,620
The 9V battery has an open circuit voltage of 7V.
Then it's dead (assuming it's a normal zinc-carbon or alkaline type) and can provide little current.
Having your MOSFET dangling on the end of long straggly wires is a recipe for disaster. If you are trying to switch the LED at high frequency (100kHz?), stray inductances/capacitances associated with the wires and with the breadboard itself can result in uncontrolled oscillations and consequent overheating of the MOSFET.

#### Devika B S

Joined Mar 8, 2017
144
Then it's dead (assuming it's a normal zinc-carbon or alkaline type) and can provide little current.
Having your MOSFET dangling on the end of long straggly wires is a recipe for disaster. If you are trying to switch the LED at high frequency (100kHz?), stray inductances/capacitances associated with the wires and with the breadboard itself can result in uncontrolled oscillations and consequent overheating of the MOSFET.
Oh! The battery is dead! How much voltage drop (open circuit) is considered dead for a battery? This 9V battery battery discharges so quickly. I have used the entire circuit totally for an hour. The next day, the battery had an OC voltage of 8.5Volts though. Today just 6.5 Volts after further usage.

#### LesJones

Joined Jan 8, 2017
2,420
You asked in the title of your thread for a current controller. That is EXACTLY what hp1729 has provided for you. The reason that your circuit destroyed itself is not the fault of the 12 volt battery. It is a fault with the design or construction of your circuit.

Les.

#### Kermit2

Joined Feb 5, 2010
4,163
Put a 100 ohm resistor in series with your battery.

OR google up a better circuit and call this attempt a learning experience.

#### Devika B S

Joined Mar 8, 2017
144
You asked in the title of your thread for a current controller. That is EXACTLY what hp1729 has provided for you. The reason that your circuit destroyed itself is not the fault of the 12 volt battery. It is a fault with the design or construction of your circuit.

Les.
I am of course not blaming the battery. It is a life less thing. Nothing to be blamed about it. I just said that I need a PWM current controller. Yeah there is a major flaw with my circuit which is why I asked for help. I had modelled it in MATLAB before putting it in hardware. This is the first time I am implementing a power electronics circuit with pwm on hardware which is why I am asking for help.

#### Devika B S

Joined Mar 8, 2017
144
Put a 100 ohm resistor in series with your battery.

OR google up a better circuit and call this attempt a learning experience.
I put a 100 ohm resistor in series with the 12V battery. Nothing happened. I mean the boost operation did not take place. Both input and output voltage remained the same. So I connected it directly.

#### Kermit2

Joined Feb 5, 2010
4,163
Build a 555 timer.

Modify the 555 into a function generator.

Use the 555 and a simple automotive bulb to make a mosfet PWM dimmer.

At this point you will have the needed experience and knowledge to make simple PWM circuits to experiment driving any type of load.

#### dl324

Joined Mar 30, 2015
9,351
Yeah there is a major flaw with my circuit which is why I asked for help. I had modelled it in MATLAB before putting it in hardware. This is the first time I am implementing a power electronics circuit with pwm on hardware which is why I am asking for help.
What is the resistance of the two inductors being used? What controls the switch?

Things burned up when using a bigger battery because the smaller one couldn't put out enough current to cause damage. You're lucky you didn't get hurt with the 12V battery. If you unsure of what you're doing, you should use fuses.

Are you trying to design a boost regulator?

#### Kermit2

Joined Feb 5, 2010
4,163
Boost operation?

I thought you wanted PWM?

I understand now why your circuit looks like a mixed up joule thief.

#### Devika B S

Joined Mar 8, 2017
144
I am of course not blaming the battery. It is a life less thing. Nothing to be blamed about it. I just said that I need a PWM current controller.
What is the resistance of the two inductors being used? What controls the switch?

Things burned up when using a bigger battery because the smaller one couldn't put out enough current to cause damage. You're lucky you didn't get hurt with the 12V battery. If you unsure of what you're doing, you should use fuses.

Are you trying to design a boost regulator?
The resistance of inductor is 15 ohms (It is a 100 uH, 2A).
The switch is controlled by an Arduino.
Yes I am not sure of the hardware. This is the first time I am doing this. I am not able to estimate how many current my circuit draws. The simulation is nothing like the hardware.

Yes I am designing a voltage boost converter. A super lift Luo converter to be precise.

#### Devika B S

Joined Mar 8, 2017
144
Boost operation?

I thought you wanted PWM?

I understand now why your circuit looks like a mixed up joule thief.
Yes it is a boost converter (12V input, 48V output expected). The MOSFET is triggered by a pulse generator in MATLAB with 66.7% duty cycle and 100 kHz frequency) in MATLAB. So I programmed this on pin 13 of arduino and the gate of MOSFET is connected to this pin.

#### dl324

Joined Mar 30, 2015
9,351
The resistance of inductor is 15 ohms (It is a 100 uH, 2A).
What is the resistance of the other inductor?
The switch is controlled by an Arduino.
Where is the feedback loop used to control output voltage?
The simulation is nothing like the hardware.
Simulators have their benefits, but nothing replaces know how and common sense.

#### Devika B S

Joined Mar 8, 2017
144
What is the resistance of the other inductor?
Where is the feedback loop used to control output voltage?
Simulators have their benefits, but nothing replaces know how and common sense.
Both the inductors have around the same resistances. One is 15 ohms and the other 20 ohms. I didn't know that a feedback loop was required. I have just done simulations and coding on MATLAB but very less hardware. In fact I have never worked with power electronics hardware like this. In labs, everything had an in built module and all I did was plug in wires from one terminal to another. No worries then. Can you tell me more about the feedback loop?

#### Devika B S

Joined Mar 8, 2017
144
Build a 555 timer.

Modify the 555 into a function generator.

Use the 555 and a simple automotive bulb to make a mosfet PWM dimmer.

At this point you will have the needed experience and knowledge to make simple PWM circuits to experiment driving any type of load.
I will try this for my next project. My present project has to be submitted on Tuesday