How to connect the low battery protection circuit and an overload protection circuit to any circuit that uses pulse width modulation IC such as SG3525, SG3524, UC3842, 43,44, TL494 etc.
Its Good to know and understand the functions of the pins of the PWM IC that you are going to add this function to. I therefore advice that you google the IC number and download its datasheet in PDF or any readable format.
Every pulse width modulation IC has either of these functional pins: Shutdown or current sense (Is) or even both in some ICs.
This post was requested by Mr. Amon from Asamankese (E/R).
The function of the shutdown pin of any pulse width modulation (PWM) IC is to safely stop or turn off the PWM IC when the pin senses voltage higher than its operating point (threshold). After the IC has turned off, the system will turn on only when the cause for increased pin voltage is removed or reset.
The current sense pin works the same way as the shutdown pin. When the pin dedicated for current sensing sees voltage higher or equal as the threshold voltage, the IC temporally, stops operating in other to save the system. The IC will begin to work normal again after the cause of overload is removed.
Current sense and shutdown pins responds to voltage within 0.3V to 5V with little current in milli ampere (mA). This means that if we are able to provide a circuit that will deliver 0.3V to 5V or above during low battery or overload, our aim of designing a low battery and overload protection circuit will be fulfilled.
Many people have the problem of sensing overload current in power system circuits. Their main problem has been either they are not getting a small resistor value which is usually called SHUNT or They are not getting a good length of AWG to provide a resistance value in Milli ohm. Personally, i prefer using AWG copper since its always common than real shunt resistors.
Overload current can be sensed either at the DC side or AC side. Its advisable to sense inverter overloads at the DC side. In that case, Mosfets can be used as Shunt resistors since they have some resistance in milli ohms even when they are fully turned on. Connecting the mosfets in parallel is same as connecting its internal resistance in parallel and hence forming low resistance shunt.
One thing to know is that before you can choose a good shunt value, you have to know the maximum current you want to switch and the voltage drop that must occur. This can be known using simple ohms law: V=IR where V is the maximum voltage drop that should occur at maximum current I. R is the shunt resistor value. Read the power drive stage of this post to learn how to calculate max current.
The circuit below shows how to sense overload DC current and connect it to the current sense pin of a PWM IC.
I have already writing about low battery protection for battery powered devices and explained the circuit operation. I will therefore move on to show you how to connect this updated circuit to any pulse width modulation IC to shut your system off when battery runs low so that your battery doesn't over drain.
A shunt resistor is a small value resistor or resistive device connected in a circuit mostly for the purpose of current sensing.
In the above circuit, the mosfet stage is connected to the shunt resistor which is connected in series with the negative supply of the battery. Please ensure that only the mosfets are connected to this part. all other sections of your inverter should be connected before your shunt. shunt size should be calculated by you based on your max current as discussed earlier.
Adjust U3 to set your low battery shutdown.
Adjust U2 to set your battery low alarm
Its Good to know and understand the functions of the pins of the PWM IC that you are going to add this function to. I therefore advice that you google the IC number and download its datasheet in PDF or any readable format.
Every pulse width modulation IC has either of these functional pins: Shutdown or current sense (Is) or even both in some ICs.
This post was requested by Mr. Amon from Asamankese (E/R).
LOW BATTERY AND OVERLOAD PROTECTION FOR PWM IC
FUNCTIONS OF SHUTDOWN PIN
The function of the shutdown pin of any pulse width modulation (PWM) IC is to safely stop or turn off the PWM IC when the pin senses voltage higher than its operating point (threshold). After the IC has turned off, the system will turn on only when the cause for increased pin voltage is removed or reset.
FUNCTION OF CURRENT SENSE (Is) PIN
The current sense pin works the same way as the shutdown pin. When the pin dedicated for current sensing sees voltage higher or equal as the threshold voltage, the IC temporally, stops operating in other to save the system. The IC will begin to work normal again after the cause of overload is removed.
Current sense and shutdown pins responds to voltage within 0.3V to 5V with little current in milli ampere (mA). This means that if we are able to provide a circuit that will deliver 0.3V to 5V or above during low battery or overload, our aim of designing a low battery and overload protection circuit will be fulfilled.
HOW TO SENSE OVERLOAD CURRENT
Many people have the problem of sensing overload current in power system circuits. Their main problem has been either they are not getting a small resistor value which is usually called SHUNT or They are not getting a good length of AWG to provide a resistance value in Milli ohm. Personally, i prefer using AWG copper since its always common than real shunt resistors.
Overload current can be sensed either at the DC side or AC side. Its advisable to sense inverter overloads at the DC side. In that case, Mosfets can be used as Shunt resistors since they have some resistance in milli ohms even when they are fully turned on. Connecting the mosfets in parallel is same as connecting its internal resistance in parallel and hence forming low resistance shunt.
One thing to know is that before you can choose a good shunt value, you have to know the maximum current you want to switch and the voltage drop that must occur. This can be known using simple ohms law: V=IR where V is the maximum voltage drop that should occur at maximum current I. R is the shunt resistor value. Read the power drive stage of this post to learn how to calculate max current.
The circuit below shows how to sense overload DC current and connect it to the current sense pin of a PWM IC.
ADDING LOW BATTERY PROTECTION TO PWM IC
I have already writing about low battery protection for battery powered devices and explained the circuit operation. I will therefore move on to show you how to connect this updated circuit to any pulse width modulation IC to shut your system off when battery runs low so that your battery doesn't over drain.
overload protection, low battery alarm and low battery shutdown circuit for inverters
A shunt resistor is a small value resistor or resistive device connected in a circuit mostly for the purpose of current sensing.
In the above circuit, the mosfet stage is connected to the shunt resistor which is connected in series with the negative supply of the battery. Please ensure that only the mosfets are connected to this part. all other sections of your inverter should be connected before your shunt. shunt size should be calculated by you based on your max current as discussed earlier.
Adjust U3 to set your low battery shutdown.
Adjust U2 to set your battery low alarm
I read that Post and got it fine and informative.
ReplyDeleteRobinets de Lavabo
Good circuit, i will try it. thanks
ReplyDeleteHello,
ReplyDeleteI wonder if anyone made this protection against deep discharge? I need something like this and I'm just wondering if everything is ok. I’ve made quite a few but they don’t work as described.
This comment has been removed by the author.
ReplyDelete