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Using Mosfet + small NPN transistor, that's the simpliest and safetest way. I am using it in my supply...ptewright said:What's the simplest way to switch on/off an 12V supply at 1A using a TTL output from a PIC microprocessor? The TTL signal may be switching between 0.5-1Hz. Should I use a MOSFET? Does anyone have any circuits?
Thanks!
Jay.slovak said:Using Mosfet + small NPN transistor, that's the simpliest and safetest way. I am using it in my supply...ptewright said:What's the simplest way to switch on/off an 12V supply at 1A using a TTL output from a PIC microprocessor? The TTL signal may be switching between 0.5-1Hz. Should I use a MOSFET? Does anyone have any circuits?
Thanks!
I have good experiences with IRF9540 P channel MOSFETljcox said:Do you want to switch +12V or -12V ?
You need a P channel MOSFET for the former but I could not find a cheap one. That is why I drew the circuit below for nppc recently, see
This circuit can be adapted for your needs.
Len
ljcox said:Do you want to switch +12V or -12V ?
You need a P channel MOSFET for the former but I could not find a cheap one. That is why I drew the circuit below for nppc recently, see
This circuit can be adapted for your needs.
Len
Looks fine, just add a resistor between the Gate and GND, just for safety if the chip is off so the motor won't spin...ptewright said:Do you think that this would work?
Is this safe for running a 1A motor?
Jay.slovak said:Looks fine, just add a resistor between the Gate and GND, just for safety if the chip is off so the motor won't spin...ptewright said:Do you think that this would work?
Is this safe for running a 1A motor?
"Calculate", anything between 1-20K will work fine. The lower resistor value, the higher curent it will suck, For example Udd=5V and R=1K, the current taken will be I=5mA... not a big deal...ptewright said:Jay.slovak said:Looks fine, just add a resistor between the Gate and GND, just for safety if the chip is off so the motor won't spin...ptewright said:Do you think that this would work?
Is this safe for running a 1A motor?
Awesome!!
Is there a way to calculate the value of that resistor, or will something like 1k be ok?
ptewright said:Do you think that this would work?
Is this safe for running a 1A motor?
ljcox said:ptewright said:Do you think that this would work?
Is this safe for running a 1A motor?
You said that the IRF540 is a P channel MOSFET but it is an N channel.
So yes it will work.
However, you should also connect a 100 ohm resistor between the PIC and the gate.
Len
I wouldn't be that sure, most IC's have outputs in high impedance or pulled-high when they are off. And that would cause motor to spin.ljcox said:I don't see the need for a resistor from the gate to gnd. If the "chip is off" as he said (I assume he means the PIC) then its outputs should be at gnd potential and so the MOSFET will be off.
Len
Jay.slovak said:I wouldn't be that sure, most IC's have outputs in high impedance or pulled-high when they are off. And that would cause motor to spin.
ljcox said:No, your diagram is correct. A P channel MOSFET would not work with a positive supply.
So the MOSFET in your diagram must be an N channel.
I don't see the need for a resistor from the gate to gnd. If the "chip is off" as he said (I assume he means the PIC) then its outputs should be at gnd potential and so the MOSFET will be off.
I would leave the diode across the motor to suppress spikes. If you only rely on the internal diode, the spike current will have to go through the supply also.
Len
What I was saying that if the IC is off (eg is in power save mode) while still powered, it's output may be pulled-up by internal or external resistor.eblc1388 said:Jay.slovak said:I wouldn't be that sure, most IC's have outputs in high impedance or pulled-high when they are off. And that would cause motor to spin.
High impedance maybe, but pulled-high is a little bit difficult when the supply is OFF. Can you quote any examples?